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Choosing HVAC Equipment for an Energy-Efficient Home

If you’re building a new green home, you’ll find that most available furnaces and air conditioners are oversized

Posted on Apr 26 2013 by user-756436

Why are the smallest available American furnaces rated at about 40,000 Btuh? Back in the 1960s, a house in a cold climate may have needed such a powerful furnace — or even one rated at 60,000 or 80,000 Btuh. But these days, many new homes have design heating loads that are much smaller — as low as 10,000 to 20,000 Btuh. Over the past 30 years, building envelopes have become tighter and better insulated, but U.S. furnace manufacturers haven’t kept up with the times. For mysterious reasons, they don’t offer furnaces that are small enough for today’s energy-conscious builders.

I wrote about this frustrating problem in a 2009 article, “Heating a Tight, Well-Insulated House.” In the four years since the article was written, furnace manufacturers haven’t budged; their smallest models are still twice as big as most energy-efficient builders need.

John Straube outlines the problem

John Straube is a professor of building envelope science at the University of Waterloo in Canada, as well as a principal at the Building Science Corporation in Massachusetts. Straube has been wrestling for years with the question of how to heat small, energy-efficient homes. On February 7, 2013, Straube gave a presentation on the topic (“HVAC for Low-Load Buildings”) at the Better Buildings by Design conference in Burlington, Vermont.

Straube defines a low-load house as one with a design heat load of less than 25,000 Btuh or a design cooling load of less than 1.5 tons. Homes like this are increasingly common. “Peak demand for superinsulated houses of 2,000 square feet is often 20,000 btuh or less, and townhouses can be under 12,000 btuh,” Straube noted in Burlington.

Finding the right equipment is hard

If you install conventional (oversized) equipment in a low-load building, says Straube, “You get a choice of freezing or cooking.”

Builders in Ontario are now reporting comfort complaints from homeowners in new homes with oversized furnaces. “The furnace turns on for four minutes, and the living room thermostat is satisfied, so the furnace turns off,” said Straube. “But the master bedroom is at the end of a long duct run, and the bedroom is still cold. The furnace can’t even heat up the ductwork. Dozens of builders are telling us this is happening. The homeowners say, ‘I have one of those low-energy houses, and I could never keep my bedroom warm.””

Persistent shoppers may be able to locate low-load heating equipment — but the cost is high, and obtaining parts or competent repair service is often problematic. “Maybe you can import stuff from other parts of the world,” Straube suggested. “But that is fraught with risk, because there are no local suppliers. Or you can try using equipment designed for sailboats.”

Small furnaces, even when available, are expensive

Needless to say, if you buy a tiny boiler from Germany or a small stainless-steel stove designed for boats, the equipment will cost an arm and a leg.

“Standard units are cheap,” said Straube. “Small units are usually more expensive. You have to pay 50% to 200% more to buy a product that is half the size. The PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. crowd used to say, ‘We will downsize the heating system and save a lot of money and put it in the insulation.’ Well, that may work in Europe, but it doesn’t work here.”

Domestic hot water loads aren't dropping

Although heating and cooling loads in new homes are lower than those in older, leakier homes, most families use just as much domestic hot water as they always have. “You can’t ignore domestic hot water anymore,” said Straube. “For a townhouse, the domestic hot water load is often equal to the space heating load.”

If you want to use a tankless water heater, you need an appliance with a very large burner. “If you have two hot-water fixtures on at the same time, that’s in the range of 2 to 3 gallons per minutes combined,” said Straube. “If the temperature of the incoming cold water is 40 or 50 degrees F, now you need a large heating appliance — about 75,000 Btuh minimum. But you might only need 25,000 Btuh for space heat. If you install a tankless heater with a capacity of 90,000 to 125,000 Btuh, which is typical for Americans in a northern climate, you end up with an appliance that is four times the capacity of your space heating needs.”

Ask yourself a series of questions

There is no simple solution to the problem of heating a low-load house. Since all available solutions involve compromises, you’ll end up choosing the least-bad option. To find the right equipment, Straube suggests that you consider a series of questions:

  • Is natural gas available? Homes without access to natural gas will probably choose an all-electric solution.
  • If natural gas is available, is the minimum monthly charge worth paying? If the gas company imposes a minimum monthly charge of $12 or $15, even if you don’t use any gas, then it may not make any sense to hook up to a gas line.
  • How high are your electric rates? An all-electric house is more palatable at 8¢ per kWh than at 16¢ per kWh.
  • What fuel will you use for your water heater, clothes dryer, and kitchen stove? If you prefer to use gas for these appliances, it may make sense to use gas for space heating as well.
  • Will the house need air conditioning? Most air-conditioned homes have ducts; if you need ducts anyway, you may want to heat your home with a furnace.
  • What type of mechanical ventilation system will you have? What type of duct system will the ventilation system require?

The all-electric option

Homeowners without access to natural gas often prefer an all-electric house to one that depends on propane or fuel oil. “Some people in homes with really good envelopes are reverting back to electric resistance heat,” Straube noted. But this approach gives Straube pause. “Is the electricity low-carbon?” he asked. “In some areas, it’s hard to say. This is still a big issue. In many areas of North America, electricity is a high-carbon energy source. Heat pumps can help with this problem, since one unit of electricity can be turned into three units of heat.”

When I recently telephoned Straube, I mentioned Marc Rosenbaum’s preference for electric appliances over fuel-burning appliances. Rosenbaum argues that it makes sense to prepare for an all-electric future. After all, renewable energy sources — wind, PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow., and tidal power — are delivered as electricity. Moreover, in areas of the country with high electric rates, it already makes economic sense to invest in a residential PV system.

“I think Marc is right but, as usual, he is ahead of his time,” Straube responded. “In the time that the typical furnace will take to wear out, we won’t even be halfway to decarbonizing the grid. I have no problem with an all-electric house with PV on the roof. Anyone who puts PV on the roof is accelerating the process of decarbonizing the grid, and I salute that. But I’m usually talking to people who depend on grid power. It’s typical for a client to ask, ‘I wonder whether we should choose natural gas or an electric air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps.?’ They don’t ask, ‘I wonder whether we should choose natural gas or an air-source heat pump with $30,000 of PV on the roof?’”

Heating and cooling with ductless minisplits

One or two ductless minisplit heat pumps have enough capacity to meet the space heating and cooling needs of a well-insulated house — easily. “Fujitsu sells a ductless minisplit — the ASU12RLS2 — that is rated at 12,000 Btuh but actually has an output of 16,000 Btuh at 0 degrees,” said Straube. “The product overdelivers. I can buy it for $1,640, and it only costs me $500 to $700 to have it installed.”

The problem with ductless minisplits isn’t output; the problem is distribution of the conditioned air blowing out of the indoor units — what’s generally known as the “cold bedroom” problem.

“If you have a two-story home with three bedrooms, connecting heat to those rooms is a challenge,” said Straube. “Maybe you can install one unit upstairs in the upstairs hall, and one unit downstairs. Is it OK? How far can I push it? The master bedroom might get cold on the coldest night. With slightly tolerant customers, that might work. The best way to keep the rooms warm is to leave the doors open. If the doors are open, the temperatures will be relatively close. But if the doors are closed, the bedrooms will be 5 degrees colder than the hallway — even 10 degrees is possible. That’s OK for some people, but other people don’t like that. What temperature ranges are acceptable? The mass market is saying 3 degrees of variation from room to room. But in homes without any heat distribution to the bedrooms, when we measure the temperatures we get more than that. So, maybe you can install a little baseboard heater in each bedroom — but that can use a lot of electricity. These are the challenges.”

Some people have suggested that creative ventilation ducting — for example, a system that supplies fresh outdoor air to the living room and hallway, and exhausts stale air from the bedrooms — might equalize temperatures from room to room. Straube rejects that strategy, however. “Ventilation air doesn’t do much to move around heat,” he said. “Ten cfm of 72 degree air to a 65 degree bedroom won’t make any difference to the temperature in the bedroom at all. Open doors work better than HRV ducting.”

However, some homeowners don’t mind cool bedrooms. “There are hundreds of thousands of homes that have a single-point heat source — a wood stove,” said Straube. “It comes down to, ‘What are your comfort standards?’ Comfort expectations are varying. If you install this type of system, I wouldn’t say, ‘You will be comfortable.’”

If room-to-room temperature variations are unacceptable, it’s always possible to design a system with ducted minisplits. “There are units that can be attached to the ceiling — units with short ducts,” Straube said. “But then you have significantly lower efficiency with most current products.”

What about air-to-water heat pumps?

For heat pump aficionados, the ideal appliance would be an affordable, efficient air-to-water heat pump that could supply a home with both domestic hot water and space heating. According to Straube, it’s unlikely that such an appliance will ever be affordable.

“Designing an air-to-water heat pump is a challenge, because you need to heat the water to 120 degrees or more for domestic hot water,” said Straube. “Making hot water at a high COPEnergy-efficiency measurement of heating, cooling, and refrigeration appliances. COP is the ratio of useful energy output (heating or cooling) to the amount of energy put in, e.g., a heat pump with a COP of 10 puts out 10 times more energy than it uses. A higher COP indicates a more efficient device . COP is equal to the energy efficiency ratio (EER) divided by 3.415. when it is -10 degrees outside is still tricky. For a ductless minisplit, you only need 100 degree air. If you have to heat water to 120 degrees, efficiency goes down.”

Straube noted that at least one manufacturer, Daikin, is selling an air-to-water heat pump (the Daikin Altherma) in the U.S. “The prices are in some cases insane,” said Straube. “Maybe $15,000 for most systems. Given the energy consumption of these low-load houses, it’s hard to justify this kind of investment. These units have the same problem as ground-source heat pumps: the investment costs are so high that they are hard to justify considering the low heating loads.”

Advice for homes that have access to natural gas

According to Straube, “If you have natural gas, a furnace is still a good choice, as long as you buy the smallest furnace you can find, and you design your duct runs carefully so the duct runs are not too long.”

At the conference in Burlington, Straube described one “solution” to the problem of oversized furnace: you can buy a two-stage or modulating furnace, and disable the high range so that the furnace can only operate in low range. “You can snip the wires so that the high stage doesn’t work — you lock out the top stage or the top two stages. You have to go in there with the wire cutters and make changes to the furnace. This can be done with a two-stage Goodman or Trane furnace.”

When I later telephoned Straube, he clarified his advice. “In public, I can’t recommend modifying manufacturers’ equipment at all,” Straube told me. “Whether or not you can even modify a furnace depends on the model you’re talking about. It’s possible to modify a Goodman two-speed furnace, but I do not recommend the modification."

Straube went on to explain why some contractors are tempted to disable the high range of a furnace. “The way these two-speed furnaces are usually set up is that they always begin at low speed. If it is still running after, say, 7 minutes, and the thermostat is not yet satisfied, it goes to high speed. In most homes, you only need the high speed setting once in a blue moon, so disabling the high speed allows you to design a low-demand duct system. If you can be sure the furnace won’t burn more than 24,000 Btuh, you can design a smaller duct system. That’s the reason to snip the wire or adjust the dip switches. Then you know the furnace won’t go into high speed.”

Combo systems

In theory, a combo system — that is, a system that uses a single water heater to provide both domestic hot water and space heating — makes a lot of sense. After all, you end up with just one appliance instead of two; that means that you have only one burner to service and one flue to install.

In practice, however, combo systems are tricky to design. Moreover, it’s hard to find the right combination of contractors to install them, and the systems are often quirky to troubleshoot and maintain.

If you want to install a combo system, Straube advises installing a hydro-air system (that is, a system that distributes warm air through ductwork) rather than a system with hydronic distribution system (for example, one that uses fin-tube baseboards). The reason is simple: most new homes include air conditioning, so you’ll probably need ducts anyway.

Fortunately, small air handlers with copper hydronic coils are readily available. Options include the Rinnai 37AHB series hydronic furnace or an air handler from Ecologix or First Company. Straube advises that low-temperature systems — for example, systems designed for 120 degree water rather than 160 degree water — are often best. “I’ve used an Ecologix air handler with 90 degree water,” Straube said.

Combo systems based on tankless water heaters are tricky, Straube notes, unless the designer includes a buffer tank of some kind. “Instantaneous water heaters have lag times and minimum firing outputs,” said Straube. “The initial slug of water is cold. So systems with tankless water heaters should have tanks. A tank provides a buffer capacity.”

Straube often recommends tank-style condensing water heaters, which represent “a very safe solution that is pretty affordable ($2,000) and pretty efficient (over 90%).” These systems work best if the flow rate to the space heating coil is under 2 gallons per minute.

When I spoke to Straube on the phone, he elaborated. “With a tankless heater, I have to worry about coincident draws of domestic hot water and space heat. If you include a 40-gallon tank, there is so much storage capacity that you can’t really screw it up, even if you have a completely out-of-sync heating demand. The tank just smooths it all out.”

However, even systems that use a storage water heater can be somewhat tricky to design. “Use a small pump so you don’t remove all the heat output of your water heater,” Straube advised. “Otherwise you overwhelm the heating capacity of the water heater.”

Straube is aware that the history of combo systems is littered with design errors. “You need to choose a low-watt blower and a low-watt pump,” said Straube. “This requires design. That means it’s harder to get these systems into the mass market.”

A variety of solutions, all with disadvantages

Straube summed up by noting that “there is no single answer” to this problem. He listed several possible solutions, along with their disadvantages:

  • A condensing furnace plus a natural gas water heater: the furnace is too large, and the water heater is not very efficient.
  • An air-source heat pump plus a natural gas water heater: a typical heat pump (even a 2-ton unit) is probably oversized, and the water heater isn’t very efficient.
  • A tankless water heater with a small air handler: this system requires an oversized air conditioner — a 2-ton air conditioner is often too large — and combo systems are tricky to design properly.
  • A ductless minisplit unit with a conventional water heater: this system may need backup heat in very cold climates, and you still need ductwork for ventilation.

What’s on the horizon?

With so many builders frustrated by the problem of oversized furnaces, are equipment manufacturers paying any attention? Not really, according to Straube. “We’ve talked to Trane, Carrier, Lennox, and we’ve told them that we want a smaller, cheaper alternative,” said Straube. “Their response is always the same: ‘No, we’re not interested. We are not seeing any demand.’”

Martin Holladay’s previous blog: “Green Building for Beginners.”

Click here to follow Martin Holladay on Twitter.

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Apr 26, 2013 7:19 AM ET

Demand for Right Size Furnaces
by user-1050854

It is the cat chasing its own tail. The manufacturers will not make right sized equipment, so dealers can't install it. If they can't install it, they can't order it. If the manufacturer doesn't get an order, they will not make it.

I have specified Mini splits on 4 residential projects. All 1500 sf or smaller. The lowest price was 12,000 installed. Nice to see John's comments on mini-split pricing.

Apr 26, 2013 7:49 AM ET

Cooling Climate
by Steven Knapp

Hi Martin:

The article is great but seems to emphasize heating over cooling. Are the issues the same for a climate zone where there is an equal or greater need for cooling? Also, if comfort is more important than cost savings, would the best option be to installed dedicated split minis in most rooms of a well insulated house?

Apr 26, 2013 8:06 AM ET

Great article
by Acobo

Another problem with heating small heating load houses with a water heater is that when the warranty from the original installers (hopefully and HVAC/Plumber company) is over, home owners have difficult servicing issues with “regular” HVAC or plumbing companies that do not know how to work on their hydronic systems. Too bad because it is really a great solution otherwise.

Apr 26, 2013 8:15 AM ET

Response to Steven Knapp
by user-756436

In most locations in the U.S., even areas with a hot climate, you still need space heating during the winter. The problem of finding low-load heating equipment is even more acute in Georgia than it is in Minnesota, because heating loads in Georgia are lower than up north.

When you are specifying heating and cooling equipment, the first step is always a load calculation. If you need 2 tons of cooling, you have plenty of equipment to choose from. If you only need 3/4 ton of cooling, however, you're in the same boat as a Passivhaus builder looking for a furnace: all of the available equipment is oversized.

Ductless minisplits or ducted minisplits are probably the best solution. Only you can determine your comfort needs -- and whether your budget allows you to install a minisplit in every room, or just one unit to serve the whole house.

Apr 26, 2013 8:17 AM ET

by user-543035

I agree with John's evaluation of heating systems, we have been installing low load systems on all of the homes we work on and typically use very well installed air source heat pumps, (sometimes with two stage equipment where the second stage is used in place of resistance heat when the temps are below 20 degrees. And frequently a combined hydronic air handler on a condensing tank with a simple open loop system. I have one on my house that I monitored this past winter and based on our instillation it is putting out a very even 3500 BTU/hr. at a flow rate of .25 gallons per minute. If you add in waste heat from the fan and pump running at 89W the overall load is just about right. The system runs 20hrs on design days and provides uniform surface and air temperatures through out the house. We achieve the low flow rate with any manufactures smallest equipment with reduced pipe sizes. The inclination might be to use a valve but when you have confidence in your design, the simpler you keep plumping systems the more robust they are. So to archive the 3500 BTU/hr rate I used 1/4 inch mini-split refrigerant tubbing. Unconventional and very effective. Incidentally you will always be off the low end of the charts for temp and flow that the manufactures give, because even the hydronic air handler manufactures think we need 60,000BTU/hr.

We moved away from gas furnaces in California because of their incompatibility with our Air Conditioning air flows. In a climate where dehudification is not necessary, we need to move 500-600CFM per ton for efficient air conditioning. The high air conditioning air flows with a two stage furnace locked in low risks condensation in the primary heat exchanger.

Lower air temperatures are critical to success. Most engineer will design their systems to be at 120 to 140F, with registers that blow air on people. We lower our air temperatures to 90 F or less. If your moving air fast at those temperatures you don't want to blow on people. So grills should throw air out of the occupied path. That makes our heat pump or combined hydronic strategies work well.

The assumption is that only supper insulated homes will have low loads, but in much of mild California the poorly done houses have loads under 20,000BTU/hrs this is where it gets trick to use point source systems like mini splits in choped up houses. The room walls and window don't maintain as well and so the temperature drift in those spaces can be very large. Finally great duct design is critical keep the static pressure and watt draws of your fan low. It would be silly to a have a system where your air handler was using 500-1000 watts (typical condensing gas furnace install) to move the air when it could be using a 100 or less if you had paid attention to ducting.

Apr 26, 2013 8:19 AM ET

Response to Armando Cobo
by user-756436

I agree with you: most plumbers don't know how to maintain or repair a combo heating system. That's why I wrote, "It’s hard to find the right combination of contractors to install them, and the systems are often quirky to troubleshoot and maintain."

Apr 26, 2013 11:36 AM ET

Low demand is probably due to the replacement market
by user-1004076

I suspect that most furnace sales in the US are the replacement market, not the new-construction market. And even though those 60-100KBTU/hr+ behemoths installed decades ago were already way oversized for the original house on day-1, home owners are reluctant do downsize, an contractors have little incentive to educate them (even if the contractors understand the problem, which is not a safe assumption.) It's often quite difficult to convince people that their heat loads are as low as they really are, even when you can prove it with 3 minutes of pencil-scratch-on-napkin analysis on fuel use history.

In CA under Title 24 it's much harder to get away with 3,4, 5x oversizing factors on heating equipment, (even as replacements), but that's not the case for most of the US & Canada. With low-mass hot air furnaces there isn't much of an efficiency penalty to for gross oversizing, but the comfort factors are very real.

I remain unconvinced that mini-split cooling & heating in CA in better-than-code or even code-min houses is fraught with efficiency or comfort problems, so long as west-side solar gains can be well managed. This is of course easier to deal with on new construction than existing homes, but the low latent loads make temporarily overheated rooms more tolerable than it would be in more humid climates. If anything it's EASIER to be comfortable with point-source cooling & heating in CA than in the torrid southeast or New England coolth, and as fully modulating systems they have a part-load efficiency advantage over a typical 2-stage, even if not fully optimized for sensible-cooling-only.

Straube is mistaken in his criticism of Marc Rosenbaum's penchant for all-electric, at least at Rosenbaum's grid-mix:

“I think Marc is right but, as usual, he is ahead of his time,” Straube responded. “In the time that the typical furnace will take to wear out, we won’t even be halfway to decarbonizing the grid.

In Rosenbaum's MA coal-fired power is already dead, having been displaced primarily with combined-cycle natural gas, at more than 50% better thermal efficiency, and something between 25-35% of the carbon output per kwh of coal fired generation. MA is also ahead of schedule on meeting its Renewable Portfolio (RPS) target of 15% by 2020, and ~30% fraction of the local grid is from legacy nukes with low/no marginal carbon per kwh. At the current grid mix, resistance electric heating has comparable carbon footprint to mid-efficiency gas (though far more expensive) even today, and ANY heat pump technology is significantly lower-carb than condensing gas.

That's significantly MORE than "...halfway to decarbonizing the grid..." at least on Marc's region grid. Clearly the numbers will differ in high-carb grids such as UT/WY, but there are many local grids that come in lower carb than Massachusetts.

But gas v.s. electricity is the LEAST of it at New England's space heating mix, which has an a high legacy fraction of oil-fired space heating, much of which could be displaced economically with mini-splits, as outlined in this recently published policy piece from Rocky Mountain Institute:

Not only can the outputs be made more right-sized for the loads (those oil-burners are typically 3x the load), even with 15 cent electricity it's dramatically cheaper than the heating-oil at the 5 and 10 year recent averages. At the 3 year historical average it's self-funding- the mini-splits will pay for themselves on heating cost savings alone.

Apr 26, 2013 11:48 AM ET

Response to Dana Dorsett
by user-756436

You hypothesize that "Low demand is probably due to the replacement market."

You may be right. But it's really hard to gauge demand for a product that is not yet on the market.

Apr 26, 2013 4:28 PM ET

Response to Martin
by user-1004076

True, but if they were getting 100 calls a day for a 25KBTU/hr 2-stage you can bet they would at least think about putting something out there. At the moment code-min homes in New England are still mostly-OK comfort wise with a 40KBTU/hr furnace, even if it's 2x oversized for many of them. Tract builders can pick a model that can handle the biggest and leakiest house in the development with some margin and use that for ALL of the houses, independent of size & shape, site orientation, etc. as long as local codes don't penalize them for oversizing.

CA Title 24 code limits on oversizing factors may eventually provide a big enough market to get the gas-burner manufacturers to make a move, but since most homes in CA are built with air conditioning an heat pumps can handle the heat loads, heating-only appliances like gas furnaces are at something of a disadvantage there.

According to local utility company analytics I was reading last year, the average design condition heat load for existing single family homes in MA is about 13-14kilowatts, or about 44-48000BTU/hr. Even though ~2500' code min new housing comes in at about half that, the turnover in housing stock is slow- those older homes will still be around for decades (centuries) to come. Even with ongoing efforts at retrofitting higher performance, it'll be very long time indeed before the old housing stock has improved to the point that a 50K 2-stage would be so oversized as to have a comfort issue. The market for 40-60K 2-stagers has legs, even if they were oversized for ALL new housing (which they're not.)

On better-than code new housing and smaller code-min houses, there's a void, but it's pretty tiny and low-profit compared to the market as a whole, but it's also a market that can economically be met with ductless heat pumps more often than not. If the paradigm ends up shifting from ducted output fossil-burners + split-system-AC coils to Marc Rosenbaum's mini-split nirvana, that's not necessarily a bad thing, though it would be nice if the current R410A refrigerant paradigm also shifted to R744 (CO2), at a miniscule fraction of the global warming hit from refrigerant leaks. (There are already some R744 cold climate heat pump options available in Europe & Asia, not so much in N. Amer.)

Apr 26, 2013 10:34 PM ET

mini-splits ...
by jinmtvt

How many bed rooms are there in average US home nowadays ??

Fujitsu has a 9K BTU model ( 9RLS2... ) which is a little bit cheaper than the 12K model
and eve has higher efficiency ( its the 27 SEER one .. )
Why not have one installed in each bedroom if temperatures in the bedrooms are so important ??

Judging by unit prices , installing 4 single zone 9RLS units should have the approximate same
total cost a using multi head units , and still provide much higher efficiency in both cooling and heating .

The cost difference going from central large units, or fuel guzzler heating devices that still requires some AC to be installed Vs mini splits must be a real joke.

And then u get double or even triple the efficiency on energy usage.

For now, it looks like a no brainer on 95% of situations, and so many different models
and options from the 3-5 top brands that it should work in any setup.

And still get rid of the damn fuels and smokes !!

Apr 27, 2013 6:17 AM ET

Edited Apr 27, 2013 6:18 AM ET.

Ducted mini splits
by Marc Rosenbaum

Fujitsu is introducing a line of single zone ducted minisplits with high efficiency and output at low temperatures (ratings go down to -5F). The smallest unit is a 9,000 BTU/hour cooling rating but is rated at about 15,000 BTU/hour heating at 0F (I'm not at a place where I have the spec at hand). I'm planning to use one in the small house I am renovating. My recollection is that the HSPF of the small unit is 12.2.

Apr 27, 2013 6:44 AM ET

Response to Marc Rosenbaum
by user-756436

Is this the unit you are talking about?

One option for this Fujitsu minisplit line is the "Slim duct indoor unit" option.

Apr 27, 2013 6:56 AM ET

Edited Apr 27, 2013 8:23 AM ET.

Fujitsu capacity tables
by user-756436

Here is the link to the Fujitsu capacity tables:

As an example, if you pair the Fujitsu AOU18RLXFZ outdoor unit with the 9,000 Btuh indoor unit, you get a heating output of 10,270 Btuh at an outdoor temperature of 5 degrees F dry bulb.

Apr 27, 2013 1:47 PM ET

I had a discussion with a
by jinmtvt

I had a discussion with a Fujitsu rep about a week ago,
and i was told that there is a new model for zone 6-7-8 dubbed 2H ..example 9RLS2H
which is tuned down lower even, and will work down to -15f at the same efficiency than the other model @ -5F .. will get the numbers straight if i can ..but out of my head this is what i t was about.
Same pricing .

ah found it at

i believe it is a new model that just got out a few weeks ago and websites aren't all updated yet

the 9K ( 3/4 ton ) model reports a Heating Range (BTU/h): 3,100-22,000
22K ? really? wow

Apr 27, 2013 2:21 PM ET

Variable speed compressor heat pumps
by Redjeepjamie

Both Carrier and WaterFurnace have released variable speed compressor heat pumps. I just installed a 4 ton Waterfurnace geo that can deliver as little as 10,000 BTUs and it only takes about 900 watts to do it , the 3 ton system can go even lower. I see these systems as the future of HVAC especially as we increase the use of PV with a goal of net zero. Geo systems do cost more up front but the have twice the life span of air source heat pumps and more than twice the efficiency so they are well worth the extra cost. I know mini-splits are popular in the energy nerd world but the truth is my customers hate the way they look . People want attractive comfortable homes and mini-spits are lacking in both areas. Also You might want to ask a few HVAC contractors about your mini-split pricing, as a business I can't put one in for less than $4,000 and make any profit. Are you going to be at ACI ? I'd love the chance to speak with you personally.

Apr 27, 2013 2:33 PM ET

Response to Jamie Clark
by user-756436

You wrote, "You might want to ask a few HVAC contractors about your mini-split pricing, as a business I can't put one in for less than $4,000 and make any profit."

I've heard that before. I also know that Carter Scott's contractor charges him between $5,500 and $6,000 per house to install two ductless minisplit units, and John Straube's contractor charges about $2,300 to install a Fujitsu ductless minisplit.

Prices vary. But as these units become more common, it looks like the installed cost is going to drop.

Apr 27, 2013 2:45 PM ET

You can see the pricing on
by jinmtvt

You can see the pricing on you nits dot com ...
how does one charge 4000$ for a ~2000$ worth of parts mini-splits?
If you accept the price, you are to blame.

I've been quoted locally at around 3000$ installed for 12RLS2 ( 4 at a atime though .. )
and normally prices for this kind of stuff are higher here than down in the states.

The fact that you need/want to make profits doesn't have anything to do with the efficiency of the products, the way that minisplits are currently filling up for the job and have a real payback time.

What is the total cost of the geo systems you are referring to ?

I'd like to see a geo/HP system without any failures and maintenance in a 15 years period.

Because quality minis tend to do that ( take Mitsu and Daikin for example .. )
Alot of 20+years old daikin systems are still working around the world.

Apr 27, 2013 3:04 PM ET

Martin, as a professional
by Redjeepjamie

Martin, as a professional HVAC contractor I fight the one man in a van or other low ball contractors everyday . Those prices are well below what contractors should be charging. As a leader in the building science world I think you have a responsibility to quote accurate "market rate" pricing, you are doing my industry a disservice when you use the price some poor uneducated contractor is "willing" to slap it in for. Builders read a blog like yours and then expect good HVAC companies to install at prices that are unrealistic. GBA might want to start a column on how to run a successful business. There are a lot of contractors out there that are failing because they do not know the business side of their business. I enjoy your blog I just disagree with you on this issue.

Apr 27, 2013 3:59 PM ET

Response to Jin
by Redjeepjamie

Jin, it's not about profits it's about cost of doing business . With labor, workers comp, insurance, cost of trucks, maintenance , fuel , office overhead ; even an efficiently ran HVAC company needs to sell at a 40% GP just to break even, that works out to about cost times 2.
After tax credits a 3 ton geo on new construction comes out at about $13,000-$15,000 depending on specifics ( in Lexington KY and the tri-state area )
According to ACCA geo systems average 24 years and air source is 12-15. I've not seen any life span data on minis. I go back to the fact that they are unattractive to the average consumer and they do not move enough air to equally condition larger areas. I'm not anti mini on a room addition or sun poarch, I just don't see the average consumer wanting a houseful of them on a new build.

Apr 27, 2013 9:33 PM ET

JAmie: if you can pull out 3
by jinmtvt

JAmie: if you can pull out 3 tons geos at that price, good. i don't see that around here though.

But maybe your business is not a good one ??

Attractiveness has little to do on this forum, i do understand your point, but aren't we looking for efficiency here ?? I don't like much better to see 20 air traps all around the place
and fugly ducts through the basement.

Cheap minis don't and wont last .. always and electrical board failure somewhere, preventing the hole unit to work even though everything else is good, and since the no brands do not give a long warranty and there is no replacement parts..they are replaced.
But the high quality ones ( aka Daikin, Mitus and Fujitsu ..some other are up there now also )
Last a very long time, and parts are available to fix the small problems for a 15-20 years period.
( i believe mitsubishi was boosting about having parts for models of 25 years ago. .or something like that .. . i know that MEAU has for all cnc controls ..same company )

What are the prices before the taxe incentives on this kind of setup ?
and who is paying the incentives ?

Keep in mind one thing though,
it will be much harder to justify a 12-14 000$ setup in the near future,
when the loads will be much lower in high efficiency houses
where a ~3000$ split with 2-3 baseboards backup and a very simple mixed air strategy with the HRV setup will be more than what is required for the loads.

Apr 28, 2013 5:09 AM ET

Edited Apr 28, 2013 5:35 AM ET.

Response to Jamie Clark
by user-756436

When it comes to prices, I am a reporter. You have shared valuable information: in Lexington, Kentucky, a reputable HVAC contractor charges about $4,000 to install a ductless minisplit. That is one data point, and it is valuable. Thanks for sharing it.

You make a valid point about the cost of doing business, and the fact that many young contractors who own little more than a pickup truck don't understand how to run a business. As a former builder, I can validate your observation. Like most contractors, I used to be the stupid guy with a pickup truck when I started out. Like most contractors, I started out not charging enough.

A reputable contractor has insurance, pays for workman's comp for employees instead of pretending that his employees are all "independent contractors," shows up in clean clothes to discuss new jobs, cleans up the work area after every day on the job site, answers phone calls promptly, and takes care of problems during the warranty period without delay or fuss. Such a contractor also need to charge enough to afford the occasional vacation, and to build up enough capital to help the business grow.

GBA has published many articles on business issues for contractors. Here are some links:

Trade Contractor Management (Part 1 of a 5-part series)

The Business Side of the Green-Built Environment

Doing Business in the Green-Built World

The Business of Building a ‘Building Business’

How to Position Yourself as an Expert Eco-Builder

My 1st Commandment: Make Detailed Estimates

My 2nd Commandment: Don’t Give Anything Away!

My 3rd Commandment: Change Orders Are Nothing But Trouble

My 6th Commandment: Don’t Try to Be Something You’re Not

My 9th Commandment: Weak Plans & Specs = Weak Project

The Business Case for ‘Smaller Is Better’

Do It Now: Review Your Company’s Health Insurance Policy

* * * *

That's not all -- there are many more business articles on GBA. For a complete list, see this page (and the subsequent pages): Business Advisor blogs.

Apr 28, 2013 5:13 AM ET

Heat-pump longevity
by user-756436

Jamie and Jin,
Concerning the longevity of heat pumps: I think it's fair to say that no one has much data on the longevity of residential ground-source heat pump systems or ductless minisplits.

I tend to be a skeptic when I hear ground-source heat pump installers brag that their systems will run for 20 or 25 years without problems. I have heard a great many stories about ground-source heat pump systems with problems: failed parts, improper commissioning, poor performance issues that cause multiple visits with factory reps, and lightning strikes.

Apr 28, 2013 9:41 AM ET

Combo System Updates?
by DennisDipswitch

Martin,your article links to a BSC paper that is 11 years old on Hot water/Space Heating combo systems.Since that time,have any conclusions,updates or improvements been made?

It seems that one of the conclusions is that the system itself must be designed properly,and isn't as simple as the average Plumber or HVAC tech is used to installing or servicing.So,is there a proven,trusted path of design for these systems?

I get it,one point being that the usual separation of tasks for the plumbing and HVAC contractor collide on this type of system,but if you take that out of the equation,is there a reliable way to make this work,and efficiently? Am I wrong to believe that many have just thrown in the towel,and have just chosen to stay away from it?

Apr 28, 2013 10:00 AM ET

Edited Apr 28, 2013 10:03 AM ET.

Response to Dennis Dipswitch
by user-756436

Researchers, engineers, and builders continue to install, study, and monitor combo systems.

One of those researchers is Armin Rudd of the Building Science Corporation (BSC). The last time I spoke to him on this topic, he said, "BSC is not yet ready to recommend this approach to builders, because these systems have glitches that can cause major headaches.

"Beginning in the mid-1990s, we began using water heaters for space heating. We had failed check valves in Taco pumps. We had scale. You get thermosyphon flow that gets past the check valve. On some systems, we got hot water flow to the coil during cooling. You get hot water heating systems and cooling systems fighting each other. To cut that short, most of those builders went to a different system because of the problems.

"Then we started using tankless water heaters. In 2006, decided to take another look at this. We had the low flow problem. The units wouldn’t turn on unless you needed 0.6 gpm. Then we had the frequent on/off flow problem -- a lot of that. You end up with slugs of hot and cold water in the system.

"Since 2006, manufacturers have responded to these issues. They are now down to the 0.4 gpm threshold. ... We're working with NYSERDA on a pilot project up in Utica. We are now monitoring two systems, with and without a small storage tank. We're getting plugging of the inlet filter of the tankless heater. It happens a lot. The aluminum anode rod was corroding enough to plug the filter. It's a recirculation problem. If you have any recirculation, any decay of the anode rod, it will end up plugging your system. So we addressed that problem with a unit with a stainless-steel strainer. Now, it becomes an annual maintenance thing. Before that they plugged up in a matter of weeks. If you have to clean the filter once a month, that’s no good.

“We have builders asking if we are ready to recommend this type of system yet, and we are saying, 'not really.' We are still worried about the high frequency of the cleaning of the inlet filters. Building America doesn’t want to recommend a system that will give us a black eye, and we want to be sure we get the savings that we are predicting. Should we be adding a buffer tank or not? If you don’t have that, what are the problems? We're not sure yet."

In spite of Rudd's list of possible problems, plenty of builders are successfully installing these systems. The ones who are doing a good job are generally the ones who learned the hard way -- by first making four or five different design or installation errors.

Apr 28, 2013 11:02 AM ET

Are you out there? "Properly designed and installed Combo System
by DennisDipswitch

There you go again...the mysterious "Properly designed and installed Combo System".The more I search for one,the more queasy I get.

I think at one point I read a lot of Armin's research and read a lot of Building America documents and saw videos of experimental equipment combos being done in Minnesota.That whole Armin Rudd/Nyserda project was especially discouraging,with all the scale and clogging problems they had.It seemed to me the fundamental flaw was using an open system with domestic water being heated and circulated through a steel buffer tank with anode rods. The scale that quickly was produced just seems to be a failure,no matter how you try to filter it out. And I guess small cheap stainless holding tanks are just not out there?(He was trying to use a 10 gallon tank or something).

Is there any reason that you just can't keep the space heating water separate from the drinking water? I just didn't see the point in not having a large holding tank (stainles(superstor style) and a closed system heat coil/air handler.Yes,I understand that pretty much negates the reason for using a tankless heater,but there could be many reasons you may want to have your water heater(tankless),your heat coil/air handler and your storage tank all in different locations.

Apr 28, 2013 9:04 PM ET

That also brings a + on the mini's side.
by jinmtvt

How many variables need to be working all together to get the system right on a GEO/HP system ?
Then how many different problems or parts could eventually hinder the system performance or prevent it to work ??

Can we fairly assume that many workers in the HAVC trade ( many as in a large % ) are either uninterested, uninformed or just plain not smart enough to perfectly install complexe GEO/HP systems ??

When using a factory tuned/assembled system, such as mini splits in this case,
where the installer only has to install the units, without much room for errors because he ain't doing much more than connecting it and mounting it; then as no touch of the design or balance or tuning of the system ... makes it a lot more reliable performance and reliability wise.

Apr 29, 2013 4:57 AM ET

Edited Apr 29, 2013 4:59 AM ET.

Response to Dennis Dipswitch
by user-756436

Your comment confuses me. "Are you out there?" Are you talking to me, to Armin, or to an HVAC system? And does "out there" mean "listening" or "out to lunch" -- or simply "a real rather than imaginary thing"?

I don't know where you found the quote about a "properly designed and installed combo system." I don't think I used that phrase on this page.

Q. "Is there any reason that you just can't keep the space heating water separate from the drinking water?"

A. No. This can be done with a flat-plate heat exchanger, or with a condensing water heater with an integral coil.

Apr 29, 2013 6:12 AM ET

by DennisDipswitch

Martin,thanks for the morning laugh.
I will choose the answer "a real rather than imaginary thing"?

I don't know if anyone has used the phrase "a properly designed and installed combo system",because I can't find anyone who will give the definition of one. It's kind of weird that folks have been experimenting and installing a combo system for at least 12 years,but no one will endorse a proper and reliable way of implementing it.

It seems that the workarounds to fix the shortcomings,kind of negate the benefits of the system itself,like in the addition of the buffer tank,it seems to bring on a whole new set of problems.

It's one of those "oh so close,yet oh so far" scenarios.The idea behind the combo system really makes sense.If you have some examples of contractors having great success and trouble free combo systems,it would be great if they would share the knowledge.

Apr 29, 2013 6:51 AM ET

Edited Apr 29, 2013 8:24 AM ET.

Response to Dennis Dipswitch
by user-756436

The problem with these installations is that many inexpensive installations aren't supported by water heater manufacturers. If you choose a method that is supported by the water heater manufacturer, you need to invest in a very expensive water heater like the Polaris -- and your savings go out the window.

Here is a link to a Polaris document verifying that Polaris supports the use of their water heater for space heating: Polaris Residential Gas Water Heater Installation Instructions.

The Polaris water heater sells for $4,000 to $5,200 -- and that price doesn't include the cost of the air handler, pumps, etc. At that price, an inexpensive furnace starts to look like a bargain.

I'll attach an illustration from the Polaris installation manual. The illustration notes, "Massachusetts code does not allow this type of installation."

[Click on the image to enlarge it.]


Polaris water heater with space heating loop.jpg

Apr 29, 2013 8:25 AM ET

Jin, I think you have a
by Redjeepjamie

I think you have a misconception about minis as they are heat pumps ( usually) just like a conventional or a geothermal, they have the same basic refrigeration cycle, the same type of compressor, reversing valves, and most other internal parts. So it would be inaccurate to claim that they are less complicated and easier to install. Yes you do not have to deal with duct work issues ( unless you are using a ducted split of course) which does simplify that part of the install, but you still have to field charge the refrigeration which is where so many systems run into problems. By that logic a geothermal package unit would be the easiest HVAC system to install because there is little to no field refrigeration work being done. In my experience minis are just as temperamental as any other refrigerant based HVAC system and needs a professional installation to make it work properly( FYI don't ever install one for a smoker!!). Yes we as an industry have issues with a workforce that for the most part needs to raise their game.
Back to pricing variables: It is not a fair to compare price differences in geo to that of minis because minis have a very fixed amount of cost, I can get the same price on my equipment here as you can anywhere in the country. With geo the equipment cost is fixed but the drilling/trenching cost will vary wildly depending on your geology. Kentucky and most of our surrounding states are fairly low cost to drill because we have soft limestone and sandstone to work with, out west where the rock is harder it is significantly more expensive. It is also a matter of supply and demand, Texas has more geo than any other state largely because there are a whole lot of drilling companies in Texas and that keeps costs low.
As far as life span goes if a geo and a mini both have the same basic components and the mini sits outside baking in the sun and freezing in the snow while the geo sits in a comfy climate controlled basement, I'll put my money on the geo outliving the mini any day of the week.

Apr 29, 2013 9:09 AM ET

Another response to Dennis Dipswitch
by user-756436

Another water heater manufacturer that supports the use of their water heaters for space heating is Rinnai.

Details can be found in the installation manual for the Rinnai air handler.

I'm attaching an illustration of the recommended piping arrangement for a combo system using a Rinnai tankless water heater.


Rinnai combo system.jpg

Apr 29, 2013 9:29 PM ET

Modulating equipment
by user-945061

Another great article, Martin!

There's a lot of mainstream equipment on the market that has outputs in the 20,000-25,000 Btuh range. Some of it may require additional programming, but not really difficult stuff. Not perfect, but worth exploring.

I'm somewhat familiar with York's equipment. Their Affinity furnace series starts at 60,000 Btuh but modulates down to 35%. Raising both the stage 'deadband' and delay would probably equal 2 hours of continuous running at the lowest output.

Tstat instructions used by York, pg 29:

As far as I know, most of Trane's air-flow settings are also at the Tstat. Historically their high efficiency equipment (XV95) has been 2 stage, starting at 60,000 Btu max, modulating down to 38,000. Fairly certain that there's some control over 1st-2nd stage in the Tstat - they definitely aren't in the dipswitches - so installers should be able to avoid cutting. Not positive, but Trane's XC95 is probably even better, with much the same functionality as the York above.

I have no direct experience with Carrier's equipment. According to their website the infinity 98 starts at 60,000 Btuh and modulates down to 40% for ~25,000 Btuh. Again the airflow can be set up in (you guessed it) the thermostat.

Apr 29, 2013 10:53 PM ET

Martin,thanks for providing
by DennisDipswitch

Martin,thanks for providing the links and illustrations.So,there seems to be some direction given by water heater manufacturers for a combo installation.

So,let's cut to the chase,it all comes down to cost.That's the attraction of this system,and the attraction of tankless heaters as the hot water source in this system.

But it seems that a lot of effort is given to improve the thing that the tankless heater was first intended for: domestic hot water.

Armin Rudd is using the buffer tank to mostly to eliminate "cold slugs" and to improve the "low flow" response and short cycling..But the buffer tank is also causing most of the scaling and blockage problems.

So,what kind of issue would a manufacturer of a tankless heater have with using a tankless for space heat?

Apr 29, 2013 11:04 PM ET

Dennis Dipswitch: what would
by jinmtvt

Dennis Dipswitch: what would be the point in using a tankless for space heating ??

Apr 29, 2013 11:23 PM ET

Let's end up the battle already ...
by jinmtvt

Unless you've got access to a lake or very large pond, there is currently nothing that will beat air HP
efficiency because of the initial cost and the very low energy demand.

If you need more than what is currently offered with mini-splits , look into investing on insulation, because your house doesn't quality as "energy efficient home "

Now what we need are cheaper water heating airHP from the main vendors...

Apr 30, 2013 4:56 AM ET

Response to Jesse Smith
by user-756436

Thanks for explaining that some furnaces can be programmed at the thermostat. If I understand you correctly, you're telling us that the installer can lock the furnace into low range and prevent the furnace from using high range, simply by programming performed at the thermostat. I wasn't aware of that, so thanks for explaining it.

However, it still rankles that builders have to buy furnaces that are much too big, and then have to program them so that they only use 1/3 of their capacity -- just because the furnace industry won't make right-sized appliances.

Apr 30, 2013 5:00 AM ET

Edited Apr 30, 2013 5:01 AM ET.

Response to Dennis Dipswitch
by user-756436

You wrote, "Armin Rudd is using the buffer tank to mostly to eliminate 'cold slugs' and to improve the 'low flow' response and short cycling. But the buffer tank is also causing most of the scaling and blockage problems. So, what kind of issue would a manufacturer of a tankless heater have with using a tankless for space heat?"

You have properly described the current situation. Rinnai is promoting these systems, so they apparently work. Armin Rudd says that these systems have problems and benefit from the addition of a small tank, which introduces new problems.

We need feedback from builders who have installed these systems, so that we know how often these systems develop performance and maintenance problems.

Apr 30, 2013 6:12 AM ET

Response to Jin Kazama
by DennisDipswitch

Jin,the reasons for considering a tankless water heater for space heating,for me,would be:

1) Cost
You can find a decent one for $800,more efficient ones at not too much more.

Tankless heaters are small and light and can be mounted nearly anywhere.

2A)Elevated Mounting
You can get these units high off the floor,if you are concerned about flooding.

3)Sealed combustion/direct vent
Since they are small and easy to locate,they can be easily positioned for direct vent use.

4)Ability to locate different components of a heating system in their most advantageous locations

You may want to have the tankless near the garage,let's say,because it is easiest to direct vent there,you may want a heating coil/air handler in your attic,because that is where your ductwork is located,and you may want an insulated holding tank centrally located in your house,because your kitchen and bathroom plumbing is near each other and hot water could be instantaneous.

5)You need domestic hot water anyway,why not use it for hydronic heating also?

I think that "deconstructing" the boiler room and moving the boiler room components around the home holds a lot of potential.

Yes,you can do all of this with a Buderus,modulating condensing boiler($4000),see #1.

Apr 30, 2013 6:20 AM ET

Armin Rudd Buffer Tank
by DennisDipswitch

Martin,wouldn't the scaling/clogging problems that Armin Rudd was experiencing have been eliminated if his buffer tank was stainless steel?

Apr 30, 2013 7:18 AM ET

Programming furnaces
by user-945061

Exactly right Martin! Most major furnace manufacturers now have modulating equipment that can be set to run in the 20k-30kBtu/hr range, and programming the thermostats (which should be part of every furnace installation anyway) will increase the run time on the lowest stage. Of course many good houses won't need to increase the 1st stage run time - their thermostats will satisfied within ~10 minutes.

Equipment manufacturers are gradually abandoning dipswitches in favor of thermostat controls. Having evaluated dozens of systems most dipswitches aren't set correctly. Not a trivial matter as most manufacturers send blowers from the factory set for the highest possible air conditioner. It's more common to see 5 tons of airflow blowing across 3 ton equipment than it is to see properly matched airflow. I think John Straube is a brilliant guy, but partly I wonder if some of the issues above stem from installer error/confusion.

There's plenty more to rankle you about heating and cooling equipment :)

Apr 30, 2013 7:36 AM ET

Respose to Dennis Dipswitch
by user-756436

Q. "Wouldn't the scaling/clogging problems that Armin Rudd was experiencing have been eliminated if his buffer tank was stainless steel?"

A. Yes. As you pointed out, it all comes down to price. It's easy to buy stainless-steel tanks that are rated for residential water pressure. Here is one supplier. The only problem is the cost.

An 8-gallon tank costs $416.

A 12-gallon tank costs $473.

Apr 30, 2013 7:40 AM ET

Response to Jesse Smith
by user-756436

Thanks for the further information. You wrote, "Most major furnace manufacturers now have modulating equipment that can be set to run in the 20k-30k Btu/hr range, and programming the thermostats (which should be part of every furnace installation anyway) will increase the run time on the lowest stage."

That's a slight improvement over a 40,000 Btuh furnace, I suppose. But if my energy-efficient house has a design heat loss of 15,000 Btuh -- and I only need that much heat for a few hours a year, on the coldest days of January and February -- a 20,000 to 30,000 Btuh furnace still sounds oversized. But it's better than a 60,000 Btuh furnace, for sure.

May 1, 2013 5:24 PM ET

Mini-split -Plus system
by user-1118336

The answer for the central space mini-split option is electric radiant ( in the remote bedrooms (floor heat in the bathrooms; cove heater or ceiling panel in bedrooms). Cheap, easy to install, closest to "right-sizing", zonal control; no extra fan energy in the remote rooms.
The mini-split ht pump keep everyone happy during milder weather at high COP; bedroom Delta will be small; mini-split does the heavy lifting during cold snaps; the radiant keeps surfaces warm and tops-off the extra needs only when needed in remote rooms. Smallest 500 Watt radiant units may still be oversized, but you're a lot closer to right-sizing equipment and get the bonus of sleeping spaces having zonal control to the "likes" of the occupant.

During coldest weather, the COP of the mini-split is dropping off anyway. Not much of a hit on efficiency to turn on 1.0 COP heat for a small portion of the overall heating.

As for carbon, should anyone be designing a house to last 100 years based on the current estimates of carbon emissions (actually estimates of last decade's carbon figures if you're relying on eGRID). I'm lucky that many local utilities get 90% of their power from hydro and the last two coal plants in OR and WA will be off-line by the end of the decade. If you're truly worried about carbon, don't design tomorrow's buildings based upon yesterday's energy mix. Distributed generation, cogen and renewables are coming on-line as fast as coal is going off-line.

May 2, 2013 7:10 AM ET

Response to Mark Heizer
by user-756436

Others agree with your approach. In his article, Living With Point-Source Heat, Marc Rosenbaum discusses the same approach (a ductless minisplit in the living room and electric-resistance radiant ceiling panels in the bedrooms).

Marc Rosenbaum published a report of the energy used for space heating by 8 similar homes at a development in Massachusetts. Here is a link to the report:

The homes had a ductless minisplit in the living room and electric resistance radiant ceiling panels in the bedrooms. Here is the key finding: "Heat pump energy is relatively even. The electric radiant panel energy, however, varies by a factor of fourteen to one." In other words, some families used a LOT of electricity to keep their bedrooms warm. Others didn't. These systems can be very efficient -- or rather wasteful -- depending on how the occupants use the equipment.

May 2, 2013 7:45 AM ET

Edited May 2, 2013 7:48 AM ET.

Heating a home.
by Perry525

There are many areas that have soft water, that doesn't produce scale and therefore do not have this problem. Where there is hard water, this can be chemically treated to make it soft.
Water is much better than air for delivering heat, about 4,000 times, it makes sense to use water for space heating, it takes up little space and is quiet in operation. It is particularly useful for UFH, where it frees up the walls for other things.
Running a hydronic system where the home heating part is a closed circuit that includes a heat exchanger coil inside a hot water tank works perfectly. With insulated pipes, once the hot water is run in the morning - there are no cold slugs.
With these systems the size of boiler is relatively unimportant as the system is divided into zones each of which has its own thermostat driving a motorized valve, including one on the hot water tank.
As each part of the home becomes cold the valve opens the boiler fires and only that part of the system becomes hot. Meaning that only hot water is heated, or a bedroom, or lounge or all at once.

May 2, 2013 9:28 AM ET

Response to Martin on radiant
by user-1118336

Great point on the occupant training when you have radiant: the average homeowner is used the instant gratification of warm air systems. Radiant can seem "glacial" when you're in-the-moment and cold. The average customer thinks: "the higher you set the thermostat, the faster the room gets warm" and these systems spin the electric meter pretty fast. Be direct with the owner about what/how radiant reacts...and politely remind the owner: Step away from the thermostat, It's not an accelorator.

Control solutions are coming that will allow greater owner satisfaction. Already, a creative contractor could piece together a relatively low cost control system that locks out the radiant and creates a "smart" radiant tstat. Current radiant floor sensors might be used: have good PID programming for this slow reacting system (and with remote sensors, can keep the controller out of sight and 'temptation' to adjust). New z-wave (or other protocol) outlets, relays, controllers and sensors could be used to develop creative lock-outs & custom programming for less than $$ than going hydronic or adding mini-split zone to all rooms. Added bonus to integrate with other systems (lighting).

May 2, 2013 10:12 AM ET

Minisplit and baseboards
by user-1005777

My minihome had baseboard heat with mostly programmable thermostats throughout. Heating cost was about $800 a year. We added a Mitsubishi minisplit in the living room that is in the center of the house. I set the thermostats about 5 F less than the mini. It has worked beutifully over the 2 winters we have had the system. When the Grandchildren visit, I raise their rooms to a comfortable level, but the baseboards rarely come on. We live in an 9000 DHD (F) area and our heating cost is around $400 a winter. All electric at 9.85 cents /Kwhr. I am thinking of installing 6 inch ducts from the living room to the end rooms and moving 30 CFM in each direction. I can do this with a total of 3.5 watts of energy using high efficiency DC fans.

May 2, 2013 10:33 AM ET

BSC's Combi System Expert Meeting
by BuildingGeek

Martin--nice column as always, and great discussion.

If anyone is interested, the presentations and writeup from BSC's Building America meeting on combi systems is available online:

Recommendations for Applying Water Heaters in Combination Space and Domestic Water Heating Systems Workshop Westford, MA - July 31, 2011
[scroll through using green slider to see individual presentations]

Report on the Expert Meeting for Recommendations for Applying Water Heaters in Combination Space and Domestic Water Heating Systems
Armin Rudd, Kohta Ueno, Daniel Bergey, Rosie Osser

Also, in re that stainless steel tank discussion--you could also get rid of the anode rod by using a non-metallic (polybutylene) tank like a Rheem Marathon 15 or 20 gallon point of use heater. However... the cost... ~$450. Ah well... back to square one.

May 2, 2013 11:16 AM ET

A slightly different perspective...
by Jpmorgan5150

i've been meaning to write this for a while. I'm a typical American homeowner. I am almost done building a house. I'm a tightwad. I built my house as energy efficiently as possible without blowing a ton of money. My motivation was getting my bills as low as possible, I'm not really what you would call an environmentalist. I like in Western Kentucky, with some snow in the winters and brutally hot and humid summers.

I used cellulose insulation and some foam (between the floors). I built a basement and a main level, 3,550 square feet. I caulked every seam on the wall construction (top/bottom of studs, floor plate, top plate, etc.). I kept the ducts inside the envelope. I used can lights that were ICAT certified and put cellulose on top of them thick enough to stop air movement. I used radiant barrier roof decking (though it probably didn't help much with the ducts in the envelope). I did central heat and air with a ground source heat pump. I didn't do ventilation other than the bathrooms.

I didn't spend a ton of money to super insulate. I barely spent up (windows, caulk, roof decking, insulation) compared to a normal home. I spent a ton of money on the ground source heat pump and bought a Marathon storage water heater.

I have not done a blower door test, but the loads for my house are around 30,000 BTU for both cooling and heating. I put in two units, both Daikon McQuay. They are the new Inverter models (variable speed compressor and fan) that scale up to 4 ton and down to 1 ton based on load. They are impressive!

Why am I posting this? I have done a ton of research on green building. There seem to be two schools of thought on green building - the Green Building Advisor's super insulate (and spend money there) to lower the house load. There are very real comfort issues in this approach that are summed up in the article above. VERY REAL COMFORT ISSUES. I understand this is the only acceptable option for those who are concerned about the environment. Many typical consumers are not willing to spend to lower the loads if it leads to comfort issues (like me).

The other school of thought is to save money and be comfortable. Build and spend money where it makes sense to lower the loads in the house (which means minimizing air leakage). Don't spend so much it moves the house outside of normal market value. I would say Doug Rye represents this school of thought well (even though he is not always right).

My break even on the additional cost for ground source heat pump is 5 years and three months. The savings per month on utilities exceeds the additional cost per month to buy the geothermal. It makes financial sense. My house has return and supply air in every bedroom and main living room. Comfort is prioritized and the cost per month to heat and cool is guaranteed not to exceed $77/month.

I built my house for less than $110/square foot. I did some of the finishing work.

Two questions:
1. Are you all willing to recognize that the approach I took is a great middle ground that is acceptable to much of the market, while super insulating is probably never going mainstream due to the costs? I understand super insulating is the only option for many people who are sincere environmentalists (and I'm OK with that).

2. I don't understand why cellulose doesn't get more respect from this site! Foam is king, but cellulose and tons of caulk can, from many places I've read, offer similar performance in air leakage in real world settings. Blower door tests prove this. Foam has issues, per the other email. Why don't you guys love cellulose as much as you love foam?

I'm sure I'm going to get a sharp reply. Before you give it, I have thoroughly read your site and openly considered my options. I have a limited budget, and I did what made sense on my budget. I think what you recommend makes a ton of sense to the sincere environmentalists who are building a house. There is a different path that is not well represented that uses many of the recommendations you all have but costs less and is less environmentally friendly.

However, the route I chose will probably much more palatable than the route you recommend.

May 2, 2013 11:54 AM ET

Edited May 2, 2013 12:08 PM ET.

Response to Jared Morgan
by user-756436

You wrote, "I don't understand why cellulose doesn't get more respect from this site! Foam is king."

There may be some lovers of foam who write for GBA, but I'll speak for myself. Here are some quotes:

In 2010, I wrote, "If you are paying for the labor, it's hard to beat double-stud walls filled with cellulose insulation for a low-cost high-R wall."

In the same year, I also wrote, "When it comes to high-R walls, the most cost-effective option in most areas is a double 2x4 wall with a total thickness of about 12 inches, insulated with dense-packed cellulose."

In 2012, I wrote, "As long as you have enough room in your attic for deep insulation, you'll get more R-value per dollar invested with cellulose on the attic floor than with rigid foam on your ceiling."

Just two weeks ago, I wrote, "Among the most popular insulation materials specified by green builders are cellulose insulation and mineral wool insulation. For certain applications, it’s hard to beat rigid foam or spray foam, although some green builders try to minimize the use of foam insulation products."

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