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All About Water Heaters

Buying a new water heater isn’t necessarily the best way to lower your energy expenses for domestic hot water

Posted on Feb 10 2012 by Martin Holladay, GBA Advisor

If you want to save energy, there are lots of exciting appliances and building materials that you might want to specify for your home: triple-glazed windows, an efficient refrigerator, and compact fluorescent or LEDLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. lighting, for example.

When it comes to choosing a water heater, though, clarity evaporates. Simple, affordable water heaters aren’t very efficient, and efficient equipment is complicated and costly. So how do you go about choosing a water heater?

Emergency decisions

Most homeowners ignore their water heaters. About once every ten years, the average homeowner goes down to the basement or out to the garage and notices that the water heater is sitting in a pool of water.

Since the family needs to replace the leaking water heater right now, the $350 special at Home Depot (or whatever model the nearest plumber is willing to install) looks good. Although a rush replacement job is understandable under the circumstances, it's not the wisest way to choose a water heater.

Choosing a water heater

The overwhelming majority of water heaters sold in the U.S. are tank-type water heaters heated by natural gas, propane, or electric resistance elements. Tank-type water heaters are widely available and inexpensive. Of the three most common fuels, natural gas is by far the cheapest, except in a few areas of the country with very low electric rates.

If natural gas is unavailable, an electric-resistance water heater makes more sense than a propane water heater, since electric water heaters avoid potential problems with backdraftingIndoor air quality problem in which potentially dangerous combustion gases escape into the house instead of going up the chimney. and flue-gas spillage.

What if you want to heat your water more efficiently — or in a more environmentally friendly way? Well, there are many options, all of which require a much bigger investment in equipment.

Options include:

  • A condensing gas water heater
  • A gas-fired instantaneous (on-demand) heater
  • A heat-pump water heater
  • A solar hot water system
  • An indirect water heater connected to a space-heating boiler
  • A desuperheater connected to a ground-source heat pumpHome heating and cooling system that relies on the mass of the earth as the heat source and heat sink. Temperatures underground are relatively constant. Using a ground-source heat pump, heat from fluid circulated through an underground loop is transferred to and/or from the home through a heat exchanger. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps; ground-source heat pumps also perform better over a wider range of above-ground temperatures..

Most of these high-tech water heaters are more efficient than typical tank-style heaters. Unfortunately, all of these options have disadvantages:

  • Condensing gas water heaters require a condensate drain, have a long payback period, and are expensive — generally $4,000 to $8,000 for a unit with a stainless-steel tank, or $2,100 for a unit with an enameled steel tank (the Vertex). Paying that much would only makes sense if you plan to use your water heater to supply space heat as well as domestic hot water.
  • On-demand water heaters require an oversized gas supply line, are mechanically complicated, may have trouble keeping up with simultaneous demand from several fixtures, have a long payback period, and are expensive.
  • Heat-pump water heaters are noisy, mechanically complicated, rob space heat from the house during the winter, require a condensate drain, have a long payback period, and are expensive. According to energy expert Marc Rosenbaum, monitoring shows that the efficiency specifications provided by manufacturers of heat-pump water heaters are probably exaggerated.
  • Solar hot water systems require regular maintenance, complicate roofing replacement, have a long payback period, and are expensive — generally $5,000 to $9,000. Although these systems make a lot of hot water in June — in some cases, more than a family can use — they don't produce much hot water in December.
  • Indirect water heaters require a boiler — an appliance that most homes lack. During the summer, the efficiency of these systems plummets, especially for households that don't use a lot of hot water; according to Marc Rosenbaum, the summer efficiency of an indirect water heater may be as low as 10% to 20%.
  • A desuperheater requires a very expensive ground-source heat pump — an appliance that most homes lack.

What about Energy Star water heaters?

Some of the water heaters mentioned above — condensing gas water heaters, solar water heaters, on-demand gas water heaters, and heat-pump water heaters — can be purchased with an Energy Star label. However, it’s worth noting that Energy Star-labeled non-condensing gas water heaters aren’t particularly efficient (minimum EF, 0.67).

Moreover, while indirect water heaters and desuperheaters aren’t eligible to receive an Energy Star label, that doesn’t mean that these methods of water heating don’t make sense for some homes.

In short, while the Energy Star labeling program for water heaters has some logic behind it, it shouldn’t be the main criterion for choosing a water heater.

If you can put it in your garage, an inexpensive gas water heater makes sense

Atmospherically vented gas water heaters have a major disadvantage: when installed inside the conditioned envelope of your house, they are subject to backdrafting whenever a strong exhaust fan is turned on. So atmospherically vented gas water heaters are a no-no in a tight house.

If you live in a warm climate where pipes don't freeze in your garage, and if you are lucky enough to have access to natural gas, it makes perfect sense to install an inexpensive atmospherically vented gas water heater in your garage. The water heater is outside of your home's thermal envelope, so there is no backdrafting risk, and natural gas is ridiculously cheap.

Power venting reduces backdrafting — but imposes an energy penalty

One of the advantages of old-fashioned atmospherically vented gas water heaters is that they don’t need any electricity to operate. While power-vented water heaters reduce the chance that an exhaust appliance causes backdrafting, the energy required to operate these venting systems is a new electrical load.

A research report from the Saskatchewan Research Council (Robert Dumont, Case Studies of Major Home Energy Retrofits) noted, “It appears that the power-vented water heaters deliver very little energy savings when you factor in the use of the power-vent motor.” Since the electrical consumption of power-vented gas water heaters is not subject to regulation, manufacturers have little incentive to address the issue. The American Council for an Energy-Efficient Economy does not compile data on power-vent consumption. “We’re doing some testing of power-vented water heaters,” Skip Hayden, a senior research scientist at Advanced Combustion Technologies in Ottawa, told me in 2004. “In terms of electrical consumption, they are all over the place. We’ve seen some that draw 100 watts, and some that draw 200 watts.”

Scott Pigg, a senior project manager for the Energy Center of Wisconsin, has reported (in a residential ventilation study) that the median operating time for residential power-vented water heaters was 80 minutes a day, although the water heater in one monitored home ran for over 240 minutes per day. If a water heater has a 200-watt power-vent, an average family might see an annual electrical consumption of about 100 kWh, and a high-use family might see an annual electrical consumption of almost 300 kWh. “I will say this about power-vented water heaters: they’re noisy little buggers,” Pigg told me. “And any time you hear a lot of noise you know there is some energy going to waste.”

A direct-vent gas water heater that doesn't require electricity

If you are wary of the backdrafting risks of conventional gas water heaters, but are still attracted to the simplicity of a tank-style gas water heater without power venting, a good solution might be a direct-vent gas water heater from GSW Water Heating of Fergus, Ontario.

GSW makes a direct-vent sealed-combustion gas water heater that operates without electricity. Its efficiency is no better that similar conventional gas water heaters, but it is protected from backdrafting risks. According to the manufacturer, this gas water heater complies with Canada's R2000 home requirements.

A lot of hot water gets wasted

When it comes to calculating how much energy Americans use to heat water, water heater efficiency tells only a small part of the story. A large percentage of the hot water produced by most water heaters never reaches the faucet.

Because many faucets and fixtures are a long way from the water heater, it can take anywhere from 30 seconds to 3 minutes for hot water to reach a distant sink. For example, when you turn on the hot tap to wash your hands, you probably begin by using the cold water that first flows from the pipe. Just as the hot water is about to reach the tap, you shut it off because you’re done. Now all of the hot water in the pipe begins to cool off, assuring that the next time you wash your hands, you will again be using cold water — but paying for hot water.

James Lutz, a research associate supervisor at Lawrence Berkeley National Laboratory, researched hot water waste; he reported his findings in a paper, “Estimating Energy and Water Losses in Residential Hot Water Distribution Systems.” His summary: “From these calculations, about 20% of total hot water use in single-family residences seems to be wasted. Although these calculations are based on many assumptions and simplifications, the results do seem reasonable to this author and point to a significant opportunity for increasing residential energy efficiency.”

Why it takes so long for hot water to reach the faucet

If Lutz’s calculations are correct, and the average house wastes 20% of its hot water, then some houses waste much more.

The factors that affect the amount of wasted hot water include:

  • Whether the house has a compact design: stretched-out single-story homes are likely to have more waste than compact two-story homes.
  • Whether the water heater is in a basement (making it easier to locate the water heater in the center of the house) or in a garage (in other words, at one end of the house rather than the center).
  • The number of bathrooms and fixtures in the house. (Homes with many fixtures waste more water than homes with few fixtures.)
  • The diameter of the tubing supplying hot water to remote fixtures. (Small diameter tubing is preferable to large diameter tubing).

As Gary Klein, managing partner of Affiliated International Management, has pointed out in a useful series of articles (“Hot-Water Distribution Systems”), all of these factors have been trending in the wrong direction in recent years, and as a result our wait times for hot water are getting longer. In Part I of his series, Klein wrote, “Since houses are generally stretched out from the driveway to the back yard on long, skinny lots, the distance to the furthest fixture has increased to over 60 feet. … There are twice as many fixtures in the current median home as there were in 1970. The distance to the farthest fixture has more than doubled. And there are a lot more fixtures served by the trunk line. In consequence and in accordance with the plumbing code, the diameter of the trunk line has increased from 1/2 to 3/4 inch for much of its length and to 1 inch for a significant portion. This means that the cross-sectional area of the pipe has increased by a factor of 2.25 to 4.0. … In addition, water utilities have taken additional steps to reduce water consumption by promoting more-water saving fixtures. They also have reduced supply pressures, both to reduce leaks in their aging systems and pump costs and to effectively increase supply for the ever-growing population in their service areas. … In short, it now takes 18 times as long for the hot water to arrive. For example, if it used to take 5 seconds to get hot water, it now takes 90 seconds.”

In Part II of his series of articles, Klein explained why small diameter hot water tubing is preferable to large diameter tubing: “Compared to the time it takes hot water to arrive in 3/8-inch-diameter pipe at a given flow rate, it takes roughly 1.5 times as long in 1/2-inch-diameter pipe, three times as long in 3/4-inch-diameter pipe, and six times as long in 1-inch diameter pipe.”

Other ways to reduce the cost of hot water

If you want to reduce the amount of energy you use to run your old refrigerator, it makes sense to shop for a new refrigerator with a higher efficiency. But you can’t really apply the same logic to your hot water system.

If you’re not happy with your run-of-the-mill water heater, you could spend thousands of dollars on a fancy new water heater that might reduce your energy use by 15%. But if your house is wasting 25% of the hot water produced by your new equipment, it’s clear that fancy equipment alone won’t solve your energy waste problem.

Here’s a list of seven things you can do to reduce the amount of energy used for domestic hot water:

  • Design your house for an efficient pipe layout. Designers should create compact designs with as few bathrooms as possible. Bathrooms should be located close to the kitchen — directly above or below the kitchen, if possible, or close to it in a horizontal direction if the rooms are on the same floor. The water heater should be centrally located. Hot water lines to remote fixtures should be small diameter lines; in most cases, home-run manifold systems make more sense than trunk-and-branch plumbing systems.
  • Insulate your hot water pipes. Pipe insulation has only limited value, since it helps keep water hot for only 30 minutes or so. Nevertheless, insulated pipes are preferable to uninsulated pipes.
  • Install a drainwater heat recovery device. These devices consists of a coil of copper water-supply tubing wrapped around a large-diameter vertical copper drain pipe. The devices extract heat from hot water flowing down the drain and transfer the heat to cold water flowing to a showerhead. Brands include GFX, Power-Pipe, and WaterCycles. Studies show that these simple devices can save 16% to 34% of the energy used to heat domestic hot water.
  • Install low-flow fixtures and efficient appliances. If you can find a 1.75 gallon per minute showerhead that you like, you’ll use a lot less hot water than your neighbor who uses a 2.5 gallon per minute showerhead. It’s also important to consider hot-water usage specifications when choosing a dishwasher or clothes washer.
  • Consider installing a demand-controlled hot-water circulation pump. If you are stuck living in a house with a bad plumbing layout — for example, a stretched-out single-story house with a water heater in the garage, and a master bath on the opposite end of the house — consider installing a demand-controlled hot water circulation pump. This type of pump won’t turn on unless you flip a switch located in the remote bathroom. Whatever you do, however, don’t install a hot-water circulation pump that is controlled by a timer or one that runs 24 hours a day; these pumps will just increase your energy bill.
  • Wash your clothes with cold water.
  • Change your behavior. If it takes you 2 minutes to wash your hands, and it takes 2 1/2 minutes for hot water to reach your bathroom sink, it probably makes sense to use the cold-water tap instead of the hot-water tap for most hand-washing activities. Retrain yourself!

The lower your hot water usage, the fewer reasons there are to buy expensive equipment

Many American households use a lot of hot water, and our inefficient plumbing systems result in a lot of waste. However, it doesn't make much sense for families that use average or below-average amounts of hot water to invest in an expensive high-tech water heater. The savings are too small to justify the investment.

For example, energy consultant Marc Rosenbaum lives in a two-person household in Massachusetts. Marc and Jill heat their water with an electric resistance water heater that requires only about 1,100 kWh per year. (They recently hooked up a heat-pump water heater, but that's another story.) It's possible to generate that much electricity with a 1-kW photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. system that costs only $4,500 to install — even less with a tax rebate — so their household is a poor candidate for a $5,000 condensing gas-fired water heater.

That said, the more hot water your household uses, the more sense it makes to install efficient but expensive equipment.

A few radical ideas

Can we imagine better ways of reducing the amount of energy we use to make hot water?

A few years ago I visited a small town on the Caribbean island of Dominica, and stayed in a simple guest house. The house had no water heater. However, the showerhead was fat, and it had a cord dangling from the end that was plugged into the nearest outlet. An electric resistance element in the showerhead (controlled by a flow sensor) raised the temperature of the water flowing through the showerhead. Since the electrical draw of the resistance element was fixed, the user controlled the temperature by adjusting the water flow. If the flow was adjusted to a trickle, the water was very hot; if the water flow was fast, the shower was lukewarm at best.

Of course, this device looked a little frightening, but it worked. It had several virtues:

  • It only worked with low flows, so you had to save both water and electricity if you wanted a hot shower.
  • Obviously, there was no hot water wasted, because no hot water ever sat in a pipe.

It turns out that these point-of-use electric water heaters are widely used in the Caribbean and Latin America. Common brands include Marey, Coral, and Lorenzetti. (If you want, you can buy such a unit in the U.S. The Marey Heater Corporation will sell you a 110-volt model for $75, and a 220-volt Lorenzetti model is available from Casa Excel in Miami for $79. Disclaimer: I'm not sure that these water heaters meet U.S. building code requirements, so experiment with these devices at your own risk.)

The main disadvantage of these units: most of them are made for tropical countries that have incoming cold water temperatures of 70°F or 80°F. These units advertise a temperature rise of 10 F° to 30 F°; that means that they won’t heat water in Vermont to shower temperature. (The better-quality 220-volt models can provide a 122°F shower with 40°F incoming cold water, but only at a relatively low flow rate of 1 gallon per minute.)

But here’s my point: many builders of zero-energy homes are moving toward all-electric homes equipped with photovoltaic systems. If you don’t like the complexity of heat-pump water heaters, that means you’ll be heating your water with electric-resistance elements. And if you’re doing that, I think that the water-heating elements should be located at the tap to minimize hot water waste.

Calling all manufacturers: we need innovative point-of-use water heaters

Clearly, most of us can't use an electric showerhead that only raises the temperature of the incoming water by 10 F° to 30 F°. Even better engineered products, like the Stiebel Eltron Mini Tankless heater, probably cost too much to install at each faucet and only handle a slow flow rate of water. (You can buy a Stiebel Eltron Mini Tankless on the Web for about $130.)

However, I'm raising the idea of using point-of-use electric resistance water heaters for two reasons: in hopes that manufacturers will develop a wider variety of point-of-use water heaters, and to get builders and designers thinking of new ways to reduce hot water waste. (For more information on this type of water heater, see Point-of-Use Electric Tankless Water Heaters.)

The bottom line

In the meantime, I believe that there’s nothing wrong with installing an inexpensive electric resistance water heater — or, if you live in a hot climate, a heat-pump water heater. Just be sure to wrap the tank in an insulation blanket and use as little hot water as possible.

Last week’s blog: “New Green Building Products.”


Tags: , , , , , ,

Image Credits:

  1. www.lifetransplanet.com
  2. Claudio Secci - 40andnow.com
  3. Marey Heater Corporation
1.
Fri, 02/10/2012 - 08:21

Which is better?
by shane claflin

Helpful? 0

Am I better off with my current indirect system with a modulating boiler and natural gas, or an el cheapo atmospherically vented one. During the summer, I don't use much hot water at all, so firing up the boiler to maintain the hot water seems like a waste. zone 5a


2.
Fri, 02/10/2012 - 08:26

Edited Fri, 02/10/2012 - 08:30.

Response to Shane Claflin
by Martin Holladay, GBA Advisor

Helpful? 0

Shane,
If you have functioning equipment in good condition, I don't recommend that you run out and buy another appliance.

At least your fuel is inexpensive. Natural gas is very cheap, and the price is still dropping.

Consider implementing some or all of my suggestions for reducing hot water use:

  • make sure your pipe layout is as efficient as possible,
  • reduce the diameter of your tubing if necessary,
  • insulate your hot water pipes,
  • consider installing a drainwater heat recovery device,
  • make sure you have low-flow showerheads, faucets, and appliances,
  • wash your clothes with cold water, and
  • be conscious of conservation every time you turn on the tap.


3.
Fri, 02/10/2012 - 09:40

Edited Fri, 02/10/2012 - 09:41.

re
by Keith Gustafson

Helpful? 1

I think the horrible efficiency numbers for indirects are possible, but not likely. The system in my house may have been one of them. A 1970 oil boiler, kept hot year round, fired 3 times an hour for half a minute or something. With your condensing boiler you are no doubt more efficient since it is cold start[only runs when called] and over 90 percent efficient when running. I don't think I have ever seen my new[condensing] boiler run without hot water being drawn.
A regular atmospheric hot water heater is a pig. Not only does it struggle to be 70 percent efficient, but slowly dumps air past the water tank and out the chimney, cooling the tank, Conditioned air heated by your furnace. Sealed combustion may be no more efficient than atmospheric but at least it stops most of that.
A condensing gas boiler with an indirect is about as good as it gets.


4.
Fri, 02/10/2012 - 09:45

Response to Keith Gustafson
by Martin Holladay, GBA Advisor

Helpful? 1

Keith,
The summer efficiency of an indirect water heater varies depending on your level of hot water usage. Buildings with high levels of hot water usage (multifamily buildings, hotels, laundromats) will see much higher efficiencies than homes with average or low levels of hot water usage.

Marc Rosenbaum is an engineer. He measured the efficiency of a ten-year-old Buderus oil-fired boiler hooked up to an indirect tank in his Massachusetts home and concluded that the summer efficiency of the system (used only for domestic hot water, not space heating) was 10%.


5.
Fri, 02/10/2012 - 09:59

re
by Keith Gustafson

Helpful? 0

Of course it is.

Because as you later state, he uses 1100kw to provide hot water for his house a year. About 31 gallons of heating oil in that buderus. Less than a tenth of a gallon a day. While I would not expect a Buderus to be wired anything but cold start, if it was setup to keep the boiler hot 24/7 it would be even worse.. If he ran a gas tank water heater it would probably have been 5 percent efficient.

All storage hot water heaters are terrible if you do not use hot water, which is why those point of use ones are a great idea.


6.
Fri, 02/10/2012 - 10:00

Thank you
by Armando Cobo

Helpful? 0

Great article and lots of good information. Thank you.


7.
Fri, 02/10/2012 - 10:14

No, it was worse than that
by Martin Holladay, GBA Advisor

Helpful? 0

Keith,
If Marc Rosenbaum was only using 31 gallons of heating oil a year to make domestic hot water, he might have been able to live with the situation. But the situation was much worse -- he was burning 0.6 gallon of oil per day for domestic hot water only. Annualized, that's 219 gallons of oil a year.

Of course, if the Buderus is used for space heating during the winter, the efficiency situation improves. But over the summer -- let's call that 6 months -- the Buderus was burning 0.6 gallons a day, or 110 gallons for half the year.


8.
Fri, 02/10/2012 - 10:24

my numbers
by Keith Gustafson

Helpful? 0

Just as a frame of reference. I have kept track of my boiler run time over the past year. The control on the Buderus [GB125BE] records run hours and it tracks very accurately to gallons. Family of 4 with two small children, lots of laundry, dishwasher, etc, all new fixtures. We averaged .45 gallons of oil per day in the summer. Now there were sporadic heat calls till mid June[yeah I know if it was up to me there wouldn't be] and starting again in mid September. this means that at least 8 months of the year the jacket losses are in the plus column. As a fully condensing power vented units, stack losses are very low.
So we are probably at this stage of our family in the average/heavy hot water users. I have no way of tracking water usage so I cannot truly get an efficiency number.


9.
Fri, 02/10/2012 - 10:30

Edited Fri, 02/10/2012 - 10:31.

Response to Keith Gustafson
by Martin Holladay, GBA Advisor

Helpful? 0

Keith,
Thanks for sharing your numbers. It sounds like your family is using more hot water and burning less oil than Marc Rosenbaum and Jill. That's good. There are many possible reasons for the apparent difference in efficiency -- something could have been wrong with Marc's Buderus, or his basement could have been colder than yours, or the accuracy of the monitoring method at one of these houses may have been somewhat imprecise.

In any case, it's always good to have the numbers, so thanks for sharing yours.

(By the way, Marc installed a water meter on his hot water line, so he knows how many gallons of hot water he's using.)


10.
Fri, 02/10/2012 - 10:35

re
by Keith Gustafson

Helpful? 0

Boiler cannot be set up correctly. It is a bit apples to oranges, but I am willing to submit that I use 5 times more hot water than he does. My boiler is only 6 percent more efficient than his. For space reasons my tank is ~20 feet of pipe from my boiler. And I use 25 percent less oil to heat my hot water?

We would have to check with him, but his boiler must be setup to run all summer. There is no reason a Buderus needs to stay hot. He probably shuts it off in the summer now, but he needs to get a new boiler guy.....


11.
Fri, 02/10/2012 - 10:47

Response to Keith Gustafson
by Martin Holladay, GBA Advisor

Helpful? 0

Keith,
Marc got rid of his boiler -- he says he was happy to see it go up his basement stairs.

He installed a Marathon electric water heater and a rooftop PV array.

He recently installed a Geyser heat-pump water heater, and hooked it up to his Marathon tank. He's still gathering data on the Geyser. He reports that the efficiency of the Geyser is quite low during the winter.


12.
Fri, 02/10/2012 - 11:01

re
by Keith Gustafson

Helpful? 0

He sure does love buying stuff..............

We all know that outside of the NE boilers are as common as hen's teeth, but the reason I had to comment is that I would hate to see someone install a cheap gas water heater right next to their condensing gas boiler. That would be silly. A badly setup indirect[and their are certainly plenty of those] is certainly bad, Marc's was historically bad, no offense to Marc.

If you use very little hot water any tank is inefficient, but a gas atmospheric must be the worst.


13.
Fri, 02/10/2012 - 11:11

Edited Fri, 02/10/2012 - 11:14.

Two people , but active
by aj builder, Upstate NY Zone 6a

Helpful? 1

Two people , but active people so we use water like three or four. 150 gallons of oil for summer 6 months. 80+ efficient standard boiler with in boiler water coil kept at temperature of course. 150/180=.83 gallons/day. 45 degree well water.


14.
Fri, 02/10/2012 - 13:13

re
by Keith Gustafson

Helpful? 0

Ahh, do miss the old tankless coil, nothing like moving the waterbed and filling it with hot water.....of course tankless coils should go the way of waterbeds..............

sounds like you could payoff an electric tank for summertime use in about a season

do miss the waterbed tho.......


15.
Fri, 02/10/2012 - 15:27

Gravity-fed recirculation
by William Rau

Helpful? 0

Martin,

Is there a reason why you didn't consider gravity-fed recirculation as a cheaper option than a hot water circulation pump? I have a long run to my kitchen and am not sure whether a small Stiebel unit or gravity-fed recirculation would better. A Stiebel unit would be easier to install, but I am attracted to the passive design of gravity-fed recirculation, although it would involve a lot of copper pipe.


16.
Fri, 02/10/2012 - 15:39

Response to William Rau
by Martin Holladay, GBA Advisor

Helpful? 0

William Rau,
Although it's possible to install sloped piping that creates a thermosyphon loop between your water heater and a remote faucet, most energy experts recommend against that approach. The major problem with a 24-hour-a-day thermosyphon loop is that the water in the pipe loses heat (even if the loop is insulated), so your energy bill will rise.


17.
Fri, 02/10/2012 - 15:51

installation savings?
by Jack Barnes

Helpful? 0

Martin, you say that a mini-tankless would cost too much for using at each faucet, but wouldn't there be some slight plumbing savings by eliminating the hot water piping? Of course you'd still need to pipe a full bathroom for hot water to supply the tub/shower. But I've always been intrigued by the idea of using these units at powder rooms, utility sinks, etc.

Those shower mounted units are at once the ugliest and most beautiful things I've seen in quite some time!


18.
Fri, 02/10/2012 - 15:55

Edited Fri, 02/10/2012 - 15:56.

Response to Jack Barnes
by Martin Holladay, GBA Advisor

Helpful? 0

Jack,
You're right: if you can install an instantaneous electric water heater in your bathroom that is sized to handle the bathroom's load, you would save the cost of running hot-water piping to that room.


19.
Fri, 02/10/2012 - 16:07

This is such an important
by Lloyd Alter

Helpful? 0

This is such an important point, such a good article, about how simple systems are so often the best. I changed my water heater and furnace to a gas-fired instantaneous (on-demand) heater, connected to my hydronic heating system through a heat exchanger. (not legal everywhere but it is here in Ontario). The result: when it is cold out and the heater is firing to keep the house warm, I can't get a decent shower. Then there is the issue of maintenance; you have to properly flush the thing out every year. Nobody told me and last summer I had to rebuild the thing for $ 700, far more than the price of a conventional water heater. I am an architect and I know my way around a plumbing system, but this all so complex and high tech that I am in another world.

Also, any gas savings are lost by the fact that I cannot get my teenage daughter out of the shower.


20.
Fri, 02/10/2012 - 16:14

Response to Lloyd Alter
by Martin Holladay, GBA Advisor

Helpful? 0

Lloyd,
The more complicated and expensive the equipment, the bigger the maintenance headaches. I don't think there is any exception to that rule.


21.
Fri, 02/10/2012 - 16:32

Nice work!
by Kohta Ueno

Helpful? 1

Martin--very nice column. A few points to add.

I don't know if you're aware of Tom Butcher's work at Brookhaven, but he did a great study looking at efficiencies of various systems out there. He wrote a recent ASHRAE Journal article on his work, but it is summarized pretty well in a 2007 report he did:

Performance of Integrated Hydronic Heating Systems (BNL-79814-2008-IR)
http://www.revisionheat.com/pdfs/brookhaven-report.pdf

The list of tested systems is on page 5, and the results summary on page 7. The standard off the shelf atmospheric tank wasn't that bad for summertime efficiency (58%), while the atmospheric boilers with either tankless coils or sidearm tanks were pretty miserable (~40%).

This lines up with work I've been doing in my "copious free time"--logging the atmospheric boiler and sidearm tank (HT Products Superstor) in my apartment basement. 2 adults, normal working schedule, and we're burning ~20 therms/month in the summertime. The problem is that the boiler only runs maybe once or twice a day for hot water calls--and there's no purge control, so there's 12 gallons of water and a few hundred pounds of cast iron that cools from 180 F to room temperature every cycle. A quick calc suggests that this is ~8 therms/month of consumption. Why yes, I'm planning on building a roll-your-own purge control one of these days.

Another great resource is ACEEE's white paper on hot water technologies--they point out that site energy-to-taps efficiency in multifamily buildings is so lousy (1/3 of site energy to taps in a bad system, and 1/2 in a good one) that point of use electric isn't a half bad idea. It's a big 94 page report, but the relevant section is pages 85 to 90.

Emerging Hot Water Technologies and Practices for Energy Efficiency as of 2011
http://www.aceee.org/research-report/a112

A few projects that I have been involved with (new construction) used top of the line condensing tankless water heaters, and I'm pretty impressed at the end-of-the-day consumption--families of 2 or 4 burning ~3-5 therms/month. Yes, these are often houses owned by energy weirdos, um, I mean consumption-conscious occupants. But still--that's$4-9/month on natural gas.


22.
Fri, 02/10/2012 - 16:40

Response to Kohta Ueno
by Martin Holladay, GBA Advisor

Helpful? 0

Kohta,
Thanks a lot for the links to the research papers.

I'm glad to hear more voices agreeing that point-of-use electric heaters, in many situations, require less source energy (fossil fuel at the electric generating plant) than efficient oil-burning or gas-burning equipment located in a homeowner's basement.


23.
Fri, 02/10/2012 - 19:55

electric showerheads
by kevin o'meara

Helpful? 0

Your article brings back memories of staying in very cheap "hotels" that I stayed while backpacking in Peru, Educador, Bolivia. You could see the electric wire glowing in the showerhead, and hear the sizzling as the water passed over it. The scary part was turning over the switch , which was right next to the shower with dripping wet hands...scarey! On the other hand I never did run into other travelers having bad experiences or close calls. I bet the stuff was wired to at least a 240V line. It did however provide hot water, instantly and at a descent flow. Some of these were augmented by black painted 55 gallon drums sitting atop their roofs.


24.
Fri, 02/10/2012 - 22:16

Nice Article; Recirc Controller
by William Geary

Helpful? 0

Martin,

That's a nicely written article. I'm glad you pointed out how inefficient recirc pumps can be. It's amazing how may people don't consider this at all and waste huge amounts of energy.

I found a really nice little recirc pump controller that the engineers put a lot of thought into when they designed it. It is called the Redytemp and you can see it here: http://www.redytemp.com/efficienthotwatercirculation.htm

They have other models as well.

What I like about this unit is that you can control the recirc pump with three different controls, all at the same time. First it has a timer option which by itself is nothing special. Second, it has a switch input so you can run a wire pair to anywhere and activate the pump. Third, and most important, it has a thermostat control You install a temperature sensor in your water line, say at the end of your run, and adjust a thermostat so the recirc pump runs until the end of the line reaches a present temperature that you can control, and then it shuts off the recirc pump. This is great because for hand washing a temperature of 100 degrees may be plenty and you don't even try to keep the water line heated to the higher temperature of the of the hot water heater. Make sure the hot water line is insulated from the hot water heater to just past the temperature sensor location.

Then you use the timer so the recirc pump doesn't run at all during times when you're asleep or away. Even when you are home the recirc pump runs for only 20 or 30 seconds until the temperature sensor reaches a sufficient temperature.

For those who really want a recirc pump this controller makes a lot more economic sense. Smart controls can save a lot of energy over dumb controls and on/off switches.

Billy


25.
Fri, 02/10/2012 - 23:09

Low-flow sinks
by Eric Sandeen

Helpful? 0

One thing I noticed after installing low-flow aerators (1.0/1.5gpm) on my sinks is that it's almost impossible to get hot water to the tap in a hand-washing minute. The lower the flow, of course, the longer it takes to get there.

I'm aware of this, yet I still habitually turn on the hot tap. Some psychological block or something...


26.
Sat, 02/11/2012 - 01:00

Amazing
by Gordon Taylor

Helpful? -1

What an interesting discussion, and an amazing conundrum, all caused by our desire to be virtuous as we pursue the luxury of hot water. Personally, I started washing my hands with cold water about fifteen years ago, not out of virtue but because the hot water I wanted never arrived anyway! At David Butler's website, optimalenergy.com, he advocates using a small 120-v. point-of-use electric tank ("minimal heat loss," he claims), plumbed in line with the shower. By the time the POU tank runs out of water for a shower, the water from the main tank has arrived. Whatever you do, don't install the gas-fired flash water heaters we used to have in Turkey! Installed in bathrooms, they were responsible for many deaths by asphyxiation: they simply used up all the oxygen in the room. The typical solution: a series of 2-inch holes bored in the bottom of the door.


27.
Sat, 02/11/2012 - 01:21

Edited Sat, 02/11/2012 - 02:04.

nice!
by Larry Weingarten

Helpful? 0

Martin, you covered a lot of ground and mentioned points that usually get left out. There are still a few things I'd add. First is simple solar. A black 55 gallon drum in the roof works in some climates, but there is work being done on freeze resistant simple solar that will cost one to two thousand dollars and can do a meaningful fraction of the DHW. We might rethink the idea of doing 75% or more with solar as it usually makes the equipment complex and delicate. There will be more on this at the upcoming Hot Water Forum in Berkeley CA.

I'll throw in mention of maintenance on tank type heaters as a cost effective thing to do, particularly with the advent of relatively expensive FVIR units. If maintenance can help heaters to last fifty years rather than nine to twelve year average, there is a lot of potential for savings. Of course, let's only maintain well insulated tanks!

Lastly, codes get in the way of efficient distribution. Depending on water pressure, gpm needed and length of run, 3/8" or even 1/4" tube can provide adequate water much faster with much less loss. When will plumbing codes catch up to the present?

Thanks for a very nice article!

Yours, Larry


28.
Sat, 02/11/2012 - 01:50

Clarification
by Marc Rosenbaum

Helpful? 0

In order of appearance in the article and comments:

- I reported that I have been disappointed with my add-on heat pump water heater, the Geyser by Nyle, in that it appears to me that the efficiency does not match the manufacturer's claims. It's difficult to measure efficiency due to the uncertainty of the size of the standby losses that the heater must make up in addition to the energy needed to actually heat water used. The lower the water usage, the lower the system efficiency of the heat pump water heater. This is nicely documented in the Steven Winter Associates ACI paper on HPWHs. I am not in any way condemning HPWHs and in fact my company is installing a couple of integrated HPWHs with some metering to further understand their performance. I haven't claimed that they are noisy, expensive, or mechanically complicated, just that my own unit has not performed as I had expected. Please draw no further conclusions :-)

- I datalogged run time on my Buderus G115 oil boiler while it was only making DHW for about four weeks. It had a 0.5 gallon per hour (gph) nozzle and rated oil pump pressure of 145 psi which yields an oil flow rate in my understanding of about 0.6 gph (nozzles are rated at 100 psi pressure). The burner ran for just under one hour per day, in roughly twenty minute time periods, so I concluded that the boiler was using just under 0.6 gallon of fuel daily. It is possible that this is not an accurate number though no one has given me a good reason to suspect it is wildly off. At the time I hadn't done any plumbing mods so didn't have a water meter on the inlet of the water heater tank. I have had a water meter in place since some time in June 2011. From July 2011 through January 2012 (seven months) we've used 2,820 gallons of hot water, an average of slightly over 13.1 gpd. Heating that amount of water from 50F to 120F is a load of about 7,650 BTU/day. 0.6 gpd of fuel oil has an input value of about 82,800 BTU, so my overall system efficiency appears to be just under 10%. This Buderus was set up and controlled as a cold start boiler and therefore did not stay at boiler temperature except when it was firing to make DHW. I have made no claim about whether it was operating optimally yet I saw no signs during the months it was operating before we took it out that something was grossly out of whack.

- Since I noticed this boiler/indirect tank issue, I have looked for it when our potential solar clients bring us their energy bills and I've seen a pattern of surprisingly high summer oil or propane usage with boilers heating indirect DHW. Everett Barber, in his excellent book Convert Your Home To Solar Energy, notes that these systems have much lower efficiencies making DHW in the warm season. I imagine that the state-of-the-art condensing low mass boilers are much better than the boiler I had and many other people have. If Mr. Gustafson's household is using five times as much DHW as mine and uses 0.45 gpd of oil to heat it then that system efficiency is about 60%, way better than mine. It would be great if more folks measured the DHW usage as well as the energy input, we'd have more real data to work with.

. Using the HPWH for almost all of this time period has resulted in an electrical usage of about 520 kWh. I've been conservative in my energy budget estimate of 1,000 kWh to heat water for one year in my quest to take the house to zero annual net energy (much more info on my blog Thriving On Low Carbon). If this was all done with resistance heat I expect it would be in the range of 1,200 - 1,400 kWh/year, so the HPWH is definitely better than straight resistance heating even at our low DHW usage.

- The electric water heater I installed is an 85 gallon Marathon because I wanted the option to use either a HPWH or solar water heating, so I knew I'd want extra gallons of storage. If my plan was to use only electric resistance I would have used the smaller Marathon (50 gallons). The two homes in South Mountain's Eliakim's Way project that achieved net zero averaged 20.6 gpd per household and in the 50 gallon Marathon averaged 0.233 kW/gallon of DHW compared to our 0.184 kWh/gallon with (mostly) the HPWH.

- Mr. Gustafson, I hadn't quite viewed it this way, but I guess I do love to buy stuff. I learn best by doing, so I seem to have to try things out for myself, and I like to measure performance of buildings and systems. To this end, I consider myself fortunate to own a blower door, a small gaggle of Hobo dataloggers, four digital watt meters, a Fluke clamp-on multimeter, and a two channel digital thermocouple. I've been even more fortunate to have been a member of a collaborative community of practitioners, mostly through the Northeast Sustainable Energy Association, that for over thirty years has shared our discoveries, successes, and failures in a non-judgmental, mutually supportive way. Perhaps someday the online community will adopt that level of civility and caring.


29.
Sat, 02/11/2012 - 04:47

Keith, what exact heater do
by aj builder, Upstate NY Zone 6a

Helpful? 0

Keith, what exact heater do you have? Condensing, oil fired?


30.
Sat, 02/11/2012 - 06:46

Edited Sat, 02/11/2012 - 07:19.

Response to Larry Weingarten
by Martin Holladay, GBA Advisor

Helpful? 0

Larry,
Thanks very much for your comments. The black 55-gallon drum is, indeed, a time-tested solar water heater in hot climates -- but not one that is likely to gain favor for most U.S. homeowners.

DOE researchers have been hoping to discover or develop "freeze-resistant simple solar that will cost one to two thousand dollars" for years. They've imagined plastic solar collectors or some not-yet-discovered breakthrough. I'm a skeptic. Solar hot water systems have been around for a hundred years. We understand the technology, which is simple. I don't see any reason why the technology will suddenly get cheaper.

Many solar hot water proponents promote existing systems (available technology) by underestimating what the systems cost to install. Homeowners who call up a contractor to get a bid usually discover that their costs will be significantly higher than the estimate they read about in the DOE brochure.

Finally, thanks for your reminder about the importance of water heater maintenance. GBA readers should definitely check out Larry Weingarten's website, Water Heater Rescue. The site contains many extremely useful tips on ways to extend the life of your water heater.


31.
Sat, 02/11/2012 - 06:58

Edited Sat, 02/11/2012 - 06:59.

Response to Marc Rosenbaum
by Martin Holladay, GBA Advisor

Helpful? 0

Marc,
Thanks for your detailed comments, which are much appreciated. And thanks also for your data monitoring activities, and your willingness to share your data and experience with the larger geek community at events such as the recent Better Buildings by Design conference in Burlington, Vermont.

The listed disadvantages of heat-pump water heaters -- including my characterization of the devices as "noisy, mechanically complicated ... and expensive" -- were, of course, my own (as were all of the disadvantages listed for other types of water heaters). I never intended my reference to your Geyser monitoring data to imply that you shared my own views on these devices.

However, just because a device has disadvantages, doesn't mean it shouldn't be specified. Even if a HPWH is noisy, it might still be appropriate for a basement, although not necessarily for a mechanical closet near a bedroom. Even if it is expensive, it might still be appropriate if its advantages justify the investment.

That's why, in the final paragraph of my article, I noted that a heat-pump water heater might be a good choice, especially for homeowners in hot climates.

Again, Marc, thanks for sharing your knowledge. I look forward to further reports on your work to achieve net zero energy.


32.
Sat, 02/11/2012 - 09:08

re: Marc
by Keith Gustafson

Helpful? 0

Thanks for replying

I do not doubt your methodology, but three comments

you did not close the loop on fuel usage, and over a small time period it could be significant, but not out of control

You say your system ran three times a day to maintain water temp. While as I mentioned I have only had such systems with a much higher usage than yours, the system would almost never run when there was not a call for water. It has always made sense in relation to amtrol's specs of around .4 deg heatloss per hour. If one were not home it ought to run maybe once a day. Which brings me to my third point.

That aint how we measure efficiency, is it? What I mean is that to be fair you need to run the same test with a regular tank hot water heater. You know 'everyone' is going to say 'well my gas tank hwh is 67 percent efficient, that is much better than the indirect' when that is not what you have proven.

In the end with your hot water usage any storage hot water unit is going to look bad, especially in the summer when the various heat losses are of no help to you.

Now I have to dig through that Brookhaven study because that looks to be pretty interesting.

RE: AJ My boiler is a buderus gb125be, the middle sized one, cannot remember the suffix.


33.
Sat, 02/11/2012 - 11:21

Brookhaven study
by Keith Gustafson

Helpful? 1

Had a chance to to read through the study linked above in Kohta Ueno's post, and it is very cool. If you have hydronic heat it is a must read.


34.
Sat, 02/11/2012 - 13:50

point of use electric for shower
by Clinton Reddekop

Helpful? 0

Hi, I wish for that too, but unfortunately it would require too much electricity:
7.6(L/min) * 4180(J/L/degC) * 30(degC) / 60(s/min) = 15884 Watts
or about 66A at 240V. Okay that's possible with some really big wires...
I assumed raising the water temperature by 30 degrees, but I'm not sure how hot the water actually needs to be. You could try numbers you like better, but I think you still would need several tens of amps.

I wonder if, combined with a very efficient drain water heat recovery device, you could make the electricity use reasonable?


35.
Sat, 02/11/2012 - 14:11

Edited Sat, 02/11/2012 - 16:41.

Photo of "electric
by Richard Patterman

Helpful? 1

Photo of "electric showerhead" reminded me of a trip to Guatemala many years ago when my wife took cold showers for a week because the "sizzle and glow" scared the hell out of her.

Great article, good job of summarizing the options and I appreciate that you acknowledge that
with low hot water usage the cheapest, simplest system (electric tank) might be the best decision.

I'm facing a decision on a small cottege with no natural gas between small electric tank or electric tankless. I know the tank is the simple, cheap solution but my lifestyle points me toward tankless.
I'm gone alot and shower at the gym a couple times a week so my usage is extremely low.
The design has the bath and kitchen sink within 5' of the dhw heater so distribution losses will be minimal.

Another thing rarely discussed about DHW is a preheat system or buffer before the DHW heater to raise the temperature of the incoming water and decrease the energy load. Here in Colorado the incoming water is 40 to 45 degrees. If that could be passively raised to house temperature (70deg) the heating load would be decreased by more than a 1/3. This could be accomplished by putting a pressurized tank or pipe loop in the warmest room of the house (utility room or sunroom).


36.
Sat, 02/11/2012 - 16:02

electric showers, etc
by Larry Weingarten

Helpful? 0

Hello: In the UK they have electric showers that are far more powerful than the Caribbean shower heaters, running at 240 VAC and drawing from 7.5 to 10.5 Kw. These are designed to heat from cold to a useable temperature. Water pressure can be low as well, so they also have "power showers" which use a pump to move water through faster and give a stronger shower. The switch for these things in in the shower ceiling so one is less likely to get electrocuted.

Responding to Richard Patterman, it used to be that when electric heaters were new in the world, tempering tanks were suggested as a pre-heater. Electric heaters had 800 or 1000 watt elements and needed something to help them perform. Any warm place in or around a house is potentially useful for getting water closer to a useable temperature. The lines between solar and pre-heating begin to blur.

Yours, Larry


37.
Sat, 02/11/2012 - 17:13

Electric showers from the U.K.
by Martin Holladay, GBA Advisor

Helpful? 0

Larry,
Thanks, Larry. If anyone is interested in more information on "electric showers" from the U.K., here is a relevant web page:
http://www.bellabathrooms.co.uk/electric_showers.html

Using an uninsulated metal water tank to pre-heat cold water before the water is heated by an electric element will work, of course. But in winter, such tanks will rob space heat from the house, and in summer such tanks will sweat.


38.
Sun, 02/12/2012 - 11:44

Efficiency
by Marc Rosenbaum

Helpful? 0

Mr. Gustafson

My oil system ran three times daily presumably because the losses off of the Aero indirect tank were such that they exceeded 0.4 F per hour. This is not uncommon because the standby losses aren't only off of the tank, but from the piping connected to the tank as well.

The efficiency I reported is the overall system efficiency, not the boiler efficiency. Since I'm concerned ultimately with actual fuel usage, this is what I set out to measure. The claim I'm making is that the system efficiency is about 10% with my low usage.

It was not my intent to run a study of other systems (though my measurements on our 8 Eliakim's Way homes, and my own, furthers that aim) so I had no need to be "fair". We need better data on all of these systems in actual usage, to determine system efficiency. Indeed, please put a water meter on your inlet line and tell us what your system efficiency is, with your system, at your usage.


39.
Sun, 02/12/2012 - 14:32

Edited Sun, 02/12/2012 - 14:34.

re:
by Keith Gustafson

Helpful? 0

Mr Rosenbaum

My sole real critique is that in rating your system at 10 percent efficient you have failed to give any comparison to any other system. If you had an electric water heater what would its efficiency have been?

If you had been gone for a week, what would your system efficiency be?

Zero.

No matter what method of heating stored hot water you used

Not really a useful number

If you have read the link Brookhaven report, they did a pretty interesting comparison. While they do not list any brand names, it is pretty apparent that they used the non condensing version of my boiler for one of their test subjects[well insulated cast iron]. If I were to measure my water usage an it came out statistically different, who would you trust?

Another interesting piece of data is that while many of the systems suffered in summertime efficiency, when looking at it as a full year they are not so bad, and in fact superior in some instances.

I keep saying the same thing in different ways, that there is no storage hot water system that would have performed well in your test setup, thus you have not told us anything in relation to the efficiency of indirect hot water heaters, but only of storage hot water heaters for households with very low hot water usage.

The brookhaven study tells us that a boiler with a well setup control strategy can give superior performance to a separate gas hot water heater for 'average' hot water usage. It does not tell us what would be the case at your usage level, although using your data point one could make an educated guess.

People will walk away after reading your numbers thinking, 'indirects stink'. Well, no that is not really so. Storage hot water heaters stink.

Your comments do not make that distinction, and I think it is an important one.

I am sorry if you think my comments are rude or somehow personally biased against you. If I have come off that way, I apologize.


40.
Sun, 02/12/2012 - 16:17

$2,100 condensing tanks & E Star problem w split H2O heaters
by Michael Chandler, GBA Advisor

Helpful? 0

Just back from a week at the International Builders Show and catching up on e-mail etc but wanted to point out a few thoughts.

First A.O. Smith has a very good condensing tank style water heater (Vertex) in NG for $2,067 or LP for $2,118. These provide 96% eff - 100 kBtu/h direct vent sealed combustion utilizing 2" PVC flue. So the days of paying $4,000 to $6,000 for a condensing gas water heater are over. A.O. Smith also offers the NEXT Hybrid for $2,000 which marries a 100 kBtu/h 90% eff tankless water heater with a tank to eliminate the cold water sandwich and pressure drop issues common with tankless water heaters which typically restrict flow by 7 psi at 5 GPM and 20 psi at 10 GPM.

A. O. Smith also offers a split heat pump water heater with an outdoor mounted heat pump that heats an indoor tank at 35 to 171 kBtu/h for water heating (and 27 –132 kBtu/h cooling capacity.) at COP ranging between 3.9 and 4.2. I've not been able to get pricing on this model

On Ted Clifton's suggestion we used a $4,600 UniChiller split heat pump water heater on a recent combined heat and hot water project with grid tie 8KW PV array. It provides up to 135 degree F water at 36 kBtu/h with COP ranging from 2.3 at 10 degrees F to 3.4 at 55 degrees F. We have an eMonitor on it so we'll be watching to see how it measures up to it's claimed efficiency.

These units can be set with an out-door temp lock-out to shut them down and switch to back-up when the out door temp falls below 10 degrees F and can be switched to provide cooling to fan-coils in the summer if you aren't also using them for domestic hot water or have solar thermal HW for summer use.

Rheem offers a split heat pump water heater sized for domestic hot water in Australia but has not brought it to the US due the Energy Star exclusion that Martin mentioned w/ indirect heaters and desuperheaters with separate storage tanks and heating elements. Until Energy Star changes this exclusion of two-part systems it is unlikely that there will be a split heat pump water heater offered in the US market to avoid heating water by cooling the indoor air provided by the heating system.

Air Tap does offer a ducting kit for their retro-fit system to allow it to draw and exhaust outside air and many of the tank-top water heaters seem likely to be able to be modified to run with a concentric vent hood as would be used with a closet mounted PTHP hotel room heat pump. Some of the tank top systems circulate water through the upper unit and would be at risk of freezing damage if installed with outdoor air circulating through the heat exchanger. Seems like a product category waiting to happen if Energy Star doesn't change their policy soon.

I understand that Gary Klein is working on code revisions to deal with the smaller pipe sizes used in manifold and "branch and twig" hot water distribution schemes he's been working on to address the modern low-flow WaterSense fixtures. He is also working with an organization called "Green Plumbers" to train American plumbing companies on the new piping strategies.

That's all for now


41.
Sun, 02/12/2012 - 16:56

PEX
by David Zentner

Helpful? 0

Any comments on using smaller diameter PEX to replace 3/4" copper hot water pipes? Are the heat losses less with PEX. I have a 40' run from the garage to the bathrooms.


42.
Sun, 02/12/2012 - 19:55

Do storage water heaters stink?
by Marc Rosenbaum

Helpful? 0

The 8 home data set I mentioned above had two homes that averaged 20.6 gpd of DHW and made that with 0.233 kWh/gallon in a 50 gallon Marathon electric water heater. At a temperature rise of 70F, that's over 70% system efficiency. So that's a fairly low DHW usage rate with a decent system efficiency.


43.
Mon, 02/13/2012 - 02:44

Great article
by Steven Hunyady

Helpful? 0

Thanks, Martin, for another great article. Your last invocation for thoughts about POU HW brings to mind an obvious idea: why not have a POU unit for each faucet and showerhead? Each is programmed/controlled a bit differently. A pushbutton for "Handwash" and another for "Very Hot" and so on.

Regarding the power needed to heat POU water at reasonable flow and temperature rise, the key to the solution is the energy needed for the job. A hot shower, even for teenagers, does not continue indefinitely (as far as I know). If the energy needed for can be effectively stored ahead of time, then an appropriate power supply can deliver it at a higher power for a shorter time. (Think of a UPS.) (Think of a storage water heater used for the second teenager's shower.)

This fits into my armchair-engineer's interest in handling high electrical loads. I have long dreampt about geeky ideas like battery-operated microwave ovens that can be bought and used in old kitchens like mine that have inadequate wiring for modern small appliances. The daily energy use of a microwave is rather small, yet the thing blows breakers if started when the coffee's brewing. The technology is swiftly dropping in cost, and is actually already well-handled by off-grid and yacht power supplies.

Thanks again Martin, GBA, and commenters.


44.
Mon, 02/13/2012 - 06:06

Response to Michael Chandler
by Martin Holladay, GBA Advisor

Helpful? 0

Michael,
Many thanks for your detailed post, with lots of useful information. Thanks for reminding me about the Vertex, which I reviewed in the August 2006 issue of Energy Design Update. I have corrected the pricing information on condensing water heaters in light of your point about the cost of the Vertex.


45.
Mon, 02/13/2012 - 06:11

Response to David Zentner
by Martin Holladay, GBA Advisor

Helpful? 0

David,
If you have 3/4-inch copper tubing to a remote bathroom, you probably have a truck-and-branch system. If you switch to a PEX manifold system, you should be able to use 1/2-inch (or even 3/8-inch) tubing for your bathroom lavatory, which will reduce the amount of water in the line (and therefore reduce hot-water waste).

You will probably be able to reduce the line to the shower to a 1/2-inch line, depending on your water pressure, although if you enjoy baths rather than showers, a 1/2-inch line will increase the time it takes to fill the tub compared to a 3/4-inch line.

You're right that copper is more conductive than PEX, but the difference in conductivity isn't the most important factor. When it comes to heat loss from the tubing, the most important factor is whether the line is insulated -- so insulate your pipes.


46.
Mon, 02/13/2012 - 06:16

Response to Steven Hunyady
by Martin Holladay, GBA Advisor

Helpful? 0

Steven,
It's possible, of course, to have a separate point-of-use electric water heater for every single faucet, shower head, and appliance in your house. The main downside to this approach is the cost of all of those water heaters.

I'm skeptical that your idea of operating high-amp electric resistance water heaters from a battery. The battery in my off-grid house weighs 1,800 pounds and cost thousands of dollars, and I still don't like to run our microwave oven from the battery system at night, because the microwave oven is such a large draw that it pulls down the house voltage. (The rule in our house: you only get to use the microwave oven when the sun is shining or the Honda generator is running.)


47.
Mon, 02/13/2012 - 19:42

David's 40' run
by Michael Chandler, GBA Advisor

Helpful? 0

David, assuming you have water sense listed 1.5 gpm faucet aerators and 1.75 gpm shower head in that remote bath you are taking 2.7 times as long to draw hot water from that 3/4" line than you would through a 1/2" line and leaving about 16 cups in the line to cool as opposed to 6 cups if you switched to 1/2".

Elbows in the line also add to the wait and waste by mixing the water so the hot water doesn't just push the cold water ahead of itself (plug flow) but eddies at the outflows of the elbows (laminar flow) this makes the water warm up gradually as it arrives at the faucet, delaying the time it takes to get to a usable hot temperature. One more reason to use PEX as opposed to copper or CPVC.

I've attached a sketch of a piping system I used to explain this to a plumber working on a LEED-h / NGBS gold house we designed in another city.

The idea is to place a manifold (here it's five 3/4 x 3/4 x 1/2 PEX tees grouped two inches apart) as close to the water heater as possible with the 3/4 out at the end going directly to the garden tub with no side branches and each 1/2" branch feeding a separate fixture group such as a single bath room or kitchen.

in this house it meant that the 3/4" to the big tub is in the same joist bay as the 1/2" to the kitchen and the 1/2" to the master bath shower and vanity group. The plumber took some convincing but this is what it took to keep each fixture within six cups of net displacement from the water heater. 1/2" PEX is so flexible that there generally is no need for elbows between the manifold and the first tee in the fixture group, where you have more than one tee it is good practice to group them close together if possible with the end outlet going to the highest flow fixture. I buy 100' rolls of red PEX so I can cut the exact length I need and not have any couplings in the lines.

In this situation we also had to feed the island sink in the kitchen with 3/8" from the wall sink and dishwasher to meet the 6-cup goal. The cold continues to run in conventional 3/4" trunk and 1/2" branch as there is no worry about waiting for cold water. I've found that this system is a good value and easy sell to the inspectors.

I wouldn't use a single fixture home run manifold system unless every home run was 3/8" except the garden tub. You can go 93' with 3/8" for the same six cups but using 1/2" individual fixture manifold piping means that you could waste six cups at the shower and then another six at your vanity and another six at your partners vanity . in actual practice 1/2" single fixture manifolds don't make much sense compared to 1/2" fixture group piping.

Grouped hot dist.jpg


48.
Wed, 02/15/2012 - 18:27

Edited Wed, 02/15/2012 - 18:29.

One cold water supply line + pobuy showerhead heaters on Amazon
by Steven Leighton

Helpful? 0

I remember 30 years ago, in the UK, when people used those old fashioned tankless gas heaters; they were in the bathroom! With another often inside the kitchen wall mounted above the kitchen sink. Many houses had just one cold water supply line around the house which fed the point of use heaters. Why double the use of water pipe?

http://www.amazon.com/Lorenzetti-Advanced-Tankless-Showerhead-Electric/d...

In the UK you can also buy electric tankless water heaters that go under the sink. Most houses are wall mounted hot water radiator heated and have hot water through the high efficiency gas boiler so the point of demand heaters haven't really taken off.


49.
Wed, 02/15/2012 - 18:28

installed a remote switch on
by mike bazilli

Helpful? 0

installed a remote switch on our hot water recirc pump when upgrading the boiler to a condensing one this year and got the family trained to use it . love it . used to be two minutes to have hot water in the master bath. now instant on as long as you plan ahead two minutes. hot water savings and a lot of water i am thinking over the course of a year.


50.
Wed, 02/15/2012 - 18:47

Manifold distribution system
by Bob Ellenberg

Helpful? 0

Martin,
Great article. After studying all the options for several years I had come to the conclusion that for a small house and small family that only washes clothes on cold water--only a simple electric water heater made sense. However, in my last house we put in a Manibloc system and used 3/8" PEX insulated lines for all but the bathtubs which had direct 1/2" insulated PEX lines. The shortened time to get hot water is amazing and I will not put anyting else in a new home now.


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