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Community and Q&A

Heating and hot water

Brad H | Posted in Mechanicals on

We’re empty nesters building a new home. I’d like to bounce some ideas off of you and looking for suggestions.
Current home, 2000ft2 20yr tract home. gas forced air heat. SE exposure & we let the sun in. Current usage: 3494kwh/yr electric, 9317 kwh/yr gas. I think we’re pretty frugal with our energy consumption, we keep the stat set low during the day, and essentially off at night.
New home will be in central CO, plenty of sun. 6939 htg deg days (about the same as current location). Average low in Jan is 12.4F. AC is not needed.
Rates at new home will be $0.0866/kwh for electric and $0.0214/kwh for gas.

New house will be about 2000 SF 1 story on slab. Good southern exposure and will be suntempered with about 7% glass on south side. It will be well insulated and tight, but not passivehouse levels. The 10-20-40-60 R levels I read here sound reasonable.

I’ve pretty much decided to install rooftop PV to offset my electric consumption.
I’m strongly leaning toward hot water baseboard heat. I don’t see the value in in-floor heat except in bathrooms. Most of our heating consumption will be early morning when we wake up and turn up the heat to 62F, at least that seems to be the case today.

I’ve been thinking about trying to go net 0 by adding more PV and electric heat and hot water, but with Nat gas being so much cheaper than electric, I’m not sure I can economically justify it. I showed a picture of a minisplit heater to my wife and she said no way.
Maybe a heat pump water heater? Do they make them big enough for hydronic heat? It would be either in the garage, or in a ventilated mech room in the garage. Since quite a bit of the demand will be when it’s very cold outside it seems the COP will be pretty low.

I’ve haven’t run the numbers yet on solar hydronic, but the articles I’ve read here and elsewhere make it sound pretty uneconomical.

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Replies

  1. Reid Baldwin | | #1

    You state your natural gas usage and prices in terms of kwh. Have you baked in a conversion to electrical power units?

  2. Expert Member
    Dana Dorsett | | #2

    There are air to water heat pumps & reversible hydronic chillers, but they require a bit of design skills to set up, and the output water temps need to be fairly modest to hit mini-split efficiency. A heat pump water heater that draws it's heat from indoor air isn't a solution to heating the space, though it's a reasonable solution to heating your hot water. An EcoCute consortium or similar heat pump water heater that pulls heat from outdoor air may do it, but may have freeze-up risk or output capacity issues at your location. eg:

    https://www.greenbuildingadvisor.com/articles/dept/musings/split-system-heat-pump-water-heaters

    There are ducted mini-splits that can be properly sized for the loads down to output temps of -5F or lower. For a 2000' slab-on grade you'd have to run the mini-ducts in a ceiling service-chase below the structural attic floor & air barrier that's holding up the insulation, but that's not particularly difficult or expensive. At your mid-winter average low temps it would only have a COP of about 2, but at 40F it can be in the 4s. Your seasonal average would likely be in the 3s.

    That would still be more expensive than your natural gas pricing, but not nearly as expensive as resistance heating.

    What is the approximate 99% outside design temperature at that location?

    https://www.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf

    https://www.captiveaire.com/catalogcontent/fans/sup_mpu/doc/winter_summer_design_temps_us.pdf

    Getting to the "right" heating solution begins with the calculated heat load at the 99% outside design temperature. Without getting a handle on that number it's all pretty much a WAG. Don't guess- start calculating! Even an I=B=R spreadsheet model of the house heat load is a lot better starting place than a WAG.

    https://www.greenbuildingadvisor.com/blogs/dept/musings/how-perform-heat-loss-calculation-part-1

    https://www.greenbuildingadvisor.com/blogs/dept/musings/how-perform-heat-loss-calculation-part-2

  3. Richard McGrath | | #3

    Brad stated :
    " I've haven't run the numbers yet on solar hydronic, but the articles I've read here and elsewhere make it sound pretty uneconomical. "

    Could not be further from the truth Brad . You just have to speak and listen to the right people .

    http://www.newsminer.com/news/local_news/builder-uses-solar-power-to-heat-fairbanks-home-in-the/article_0e6654f8-6226-576b-a004-2870890894cb.html

    The technology that exists now and by folks who are willing to learn from others' mistakes make it possibly the best way to get to 0 . A proper solar thermal drainback system does not require Glycol and will operate for a good long time , panels and all .

    By using similar equipment as mentioned here EVERYDAY , but keeping the refrigerant outside . Water based systems also offer the capability of retrofitting later when approved refrigerants change to something other the amount of work required will be much less intensive and expensive . You'll also be able to utilize several different sources to heat the home and the hot water .

    Your numbers seem to suggest a use of about 318 therms (ng) or 342 gallons (LP) per year . A small Water Furnace W/W HP teamed up with a solar thermal storage tank could get you in the range of a COP of =>10 , that's system efficiency . You could also just use the same gas that you have been with a solar thermal strategy and use the water heater with an HX for space heat . NO BOILER !

    As far as emitters go , the 2 very best options available in the hydronic market are HTPs new Ultra Thin fan convectors , look similar to panel rads and operate at less than 28 Db or Smiths Environmental Heating Edge baseboard . HE2 or HE3 have the highest output at the lowest water temps of anything else readily available .

    http://htproducts.com/fan-coil.html .
    Keep in mind , these outputs are based on only 2 water temps , by using outdoor reset you increase the range exponentially .

    http://www.emersonswan.com/manufacturers-products/heating-edge.html

    http://smithsenvironmental.com/wp-content/uploads/Silent-Fin-Heating-Edge-Literature.pdf

    Don't let others misunderstanding of things or bias influence you too awfully much .

  4. Brad H | | #4

    Thanks to all.
    Reid, I converted from $/therm to kwh because I prefer to work with consistent units.
    Dana, the 99% htg temp is about -4F. I'll calc heat loads when I have a floor plan in a couple of days.
    Richard yes 318 therms. thanks for the links. I was just starting to look at 'geothermal' heat pump with solar thermal. Can you feed hot solar water as the source for a heat pump or could it be too hot?

  5. GBA Editor
    Martin Holladay | | #5

    Brad,
    For more information on space heating with air-to-water heat pumps -- an approach that I don't recommend -- see Air-to-Water Heat Pumps.

    I agree with you that buying enough solar thermal equipment to heat your house is not the best use of your money. There are cheaper ways to heat your house -- and in your climate, you won't need much space heat.

    To my mind, you have two choices:

    1. Heat your home with natural gas, because it is by far the cheapest fuel. It's hard to beat a natural-gas furnace for cost-effectiveness.

    2. Install ducted minisplits (because your wife doesn't like the look of ductless minisplits) and balance the electrical usage with roof-mounted PV. Many green builders like the all-electric approach because it eliminates the on-site burning of fossil fuels. It seems to me, however, that you should only adopt this approach if your local utility offers a favorable net-metering contract.

  6. Richard McGrath | | #6

    Brad ,

    Yes you can use stored solar thermal water and feed it to a W/W HP . Using a setpoint mixing valve between the HP and tank leverages the mass rather well and you could conceivably go weeks before reaching normal Ground source temps during thoase times when the sun offers less help .

    The lack of Glycol in systems like this make everything much more manageable , require less maintenance and give you options unlike many other POPULAR strategies that offer none of these . A couple of DC ECM circs is all you will need on the source side , solar pump and pump between tank and HP . No complicated controls and a hedge fund of sorts where heat energy is banked . Gas backup also easily fits into a designed system rather easily . This also offers the capability of pumping close to exact amounts of fluid through the HP HX and getting OPTIMUM performance no matter what conditions exist outdoors .

    I'd venture that your DHW would be damn near free during summer months . The ability to store 140* fluid and have a HP sip heated water from it at a very slow rate certainly is a good thing . Much more advantageous than putting your faith in a system whose outdoor unit has peaks and valleys in efficiency which are weather / temperature dependent .

    As stated previously though , gas just might be the way to go . By using water however you can adapt the system at any time you wish using available technology . Why limit yourself . At present that seems to be the way chosen by my client in Cotopaxi , Co . We are designing for gas and leaving future options wide open by using the Ultra Thin units and varying water temps and flow rates to match load on a moment by moment basis . You can always add A/C later with very few trials and tribulations .

    Remember , it was none of us who chose water as the best medium to move heat . Mother Nature chose for us .

  7. GBA Editor
    Martin Holladay | | #7

    Richard,
    Your contention -- the "I'd venture that your DHW would be damn near free during summer months" if the water is heated with solar thermal equipment -- was widely repeated during the 1970s, especially by popular magazines like Mother Earth News (which was famous for articles with titles like "Free Heat From the Sun!").

    But anyone who buys solar thermal equipment knows that this method of making hot water isn't free. If the equipment costs $6,000 or $8,000, you aren't getting free hot water. What you are getting is hot water that is so expensive that solar thermal installers are closing up shop all over the country.

  8. Richard McGrath | | #8

    Martin ,

    Maybe more solar thermal installers should get enough education that they are designers and stop listening to the rep agencies that sell equipment .

    Of course solar thermal as like anything else will vary by region . Systems that utilize a proper design taking all aspects into account that also provide space heating will almost always make sense .

    " PRICE IS ONLY AN ISSUE IN THE ABSENCE OF VALUE "

    You never cease to amaze me . Although we want the same end result you believe you have the ONLY ANSWER . I remember people talking about solar PV in the seventies also Martin , look where that is now . Less efficient than solar thermal and being accepted on schemes that include and depend on being grid tied . Trusting the electric monsters to do the right thing . But , as I said long ago , they acre about no one but the share holders and profit . Look at what they are already doing in Nevada , Arizona . It's a shit show and you have a front row seat . The very minute thye are selling power that was less costly to them because it was provided by ratepayers all bets will be off on you selling what you made at your site .

    Why don't uyou really join the team that will move independence forward and create a few America jobs or at least a few dollars for American owned companies .

    IOf someone installs equipment touted by you as the best and has to replace it and a majority of the components because of a change in rules on accepted refrigerant several years down the road , what good is that ? If someone wants real efficiency and has to use several individual units as opposed to a multi split , what good is that ? If someone wants a system that can change , be added to , use multiple fuel sources , what is wrong with that ?

    People closing up shops does not bother me , most of those are guys who go belly up because they listen to others and don't know the science and math for themselves . They should have learned . Under your scheme , entire companies are closing up and moving offshore to sell the stupid Americans garbage because we want CHEAP , CHEAP , CHEAP .

    Why don't you really join the team and stop bashing me at every turn . You are the Big Cheese on this particular site and when someone attempts to provide useful information to your users based on their question you always do the same thing , play the mine is bigger than yours game .

    Remember there is only one environmentally friendly refrigerant . Maybe you don't believe the seas effecting weather ? Just wait for the air source guys next attempt to address the problems they have , C02 running through your house at 1000+ psi . Better hope the labor pool is really skilled for that one !

    Brad ,

    if you'd like to discuss options or have more useful data accompanied by real world math as opposed to lab result math you can e mail me . [email protected]

  9. GBA Editor
    Martin Holladay | | #9

    Richard,
    Take a deep breath. I was merely pointing out that using solar thermal collectors to make domestic hot water doesn't mean that the hot water is "free."

    I've got two 4x8 solar thermal collectors on my roof. That's how I make my hot water during the sunny months of the year. The system works great. It isn't free, of course... but it works great.

  10. Brad H | | #10

    I appreciate every ones input even when there is disagreement. Richard, I think it would be more helpful to keep the discussion here. Are you talking about a system such as fig 39 here:?
    http://www.bine.info/en/publications/themeninfos/publikation/elektrisch-angetriebene-waermepumpen/waermepumpen-plus-solar/

    Have you designed or built a system like that? Capacity and ballpark costs?

  11. Richard McGrath | | #11

    Just for the sake of avoiding confusion , what are you most likely wanting ? Gas , Electric or Hybrid . All three would be different .

    Maybe you'd be able to tell us your load assumption and ACH natural to better make recommendations . Just because they do things one way in Europe does not necessarily make it right or better , just is what it is . The depiction in fig 39 is all electric , if that is what your end goal is then yes it would be similar with slight variations in piping such as locating the space heating to a different point to lessen the liklihood of the HP short cycling . Many things go into each individual design based on wants , needs , location , utility rates , use patterns . Asking me to give anything my blessing without knowing all the particulars will probably never happen .

    One thing I can say for certain is that I for one do not want to see the heating / cooling industry consist of magic boxes made somewhere else that are not all they are touted to be .

    Maybe I can help you decide based on actual information . If your wife does not like the look of mini split stuff , ducted or not , nor does she find baseboard or convectors attractive maybe she'd like to see nothing at all while enjoying efficient subliminal comfort , and not from the floor .

    I am here to help but often find it difficult to do here on GBA . Maybe I have a solution for your needs , shall we see ?

  12. Expert Member
    Dana Dorsett | | #12

    There is more design risk to going with an active solar thermal approach rather than simply expanding the PV array to cover the energy use of a heat pump, and often higher cost. That's not to say that it's always more expensive or never pencils out favorably, only that with any custom or semi-custom design much of the cost, reliability & performance rides in the hands of the system designer.

    Bottom line: The competence of the designer of any active solar or reversible chiller heat pump or water-to-water heat pump w/cool temperature solar needs to be carefully vetted, which can be hard to do. I believe Richard is correct that effective COPs north of 10 can be achieved with low-temp solar and water-to-water heat pumps, but the number of competent designers, installers, & service techs familiar with that approach are limited. The system cost of that approach vs. serving the load with a few more PV panels and a mini-split with a COP of 2.5-3.5 needs to be compared, since there is both lower design risk and probably lower hardware cost with the latter. If the cost difference isn't large and you can tolerate the design risk, go for it! I'd personally like to see that approach better refined, defined, standardized, and cost-reduced. But without more practitioners it risks becoming an orphaned system devoid of technical support down the line. There are probably more mini-splits installed in any given week in the US than all water-to-water heat pumps combine in any give year, let alone interesting low-temp solar thermal water-to-water hybrid systems, as clever & efficient as those systems might be.

    A mini-split is a pre-engineered "system in a can". There are fewer ways to screw it up, and more technical help available for fixing it if it doesn't perform. The more idiot-proof you make something the more creative the idiots become, but it's still a safer choice for most.

    Depending on layout and other considerations, most 2000 square foot single story homes built a "pretty good house" R-values will be with the -4F capacity of one or two 1-1.5 ton Fujitsu _ _ RLFCD dedicated mini-ducted minisplits, or a 2-3 ton Mitsubishi 2-3 zone multi-split using mini-duct cassettes:

    http://www.btureps.com/fujitsu/fujitsu-literature/2014-rlfcd-rlfcc-brochure.pdf

    http://www.mitsubishipro.com/media/989222/mxz_h2i_productlaunchbrochure1stprint.pdf

    The RFLCDs are fully specified down to -5F, the H2i Mitsubishi's down to -13F, but they both keep running at temps colder than that with an unspecified output.

  13. Richard McGrath | | #13

    Dana ,

    Take the hybrid scenario out of the question and this is as simple and uncomplicated as anything else .

    There are probably alot more competent designers and installers than most think I'd like to point out . Getting rather hard to convince people that it is effective and has a better long term cost though with articles being written by or about systems installed by geniuses who are not so much .

    How easy could it be ? Phoenix or Light Duty w/ SHX . A couple panels , drain back tank and solar controller . 1 FPHX , 2 ECM circs and emitters . Never have to worry about refrigerant changes , low electrical consumption , lowest gas usage . Sure does sound intimidating doesn't it ? The thing that really sucks is every component I just mentioned would be produced just a short distance from where you reside Dana . Don't lose sight of the OPs original question and that it included a hydronic solution .

    Me thinks that you are correct about the installed numbers and would add that this probably needs to change . No prejudice toward any country or people other than I think we really must start to employ our own and have some pride like it was when we were a country of producers instead of consumers only .

  14. GBA Editor
    Martin Holladay | | #14

    Brad,
    You wrote, "Blowing hot air down from the ceiling doesn't seem like a good practice though."

    I think that your assumption is based on your experience in leaky, poorly insulated houses. If you are building a new home, you have an opportunity to build an entirely different type of home: one that is very tight and very well insulated.

    If you build a superinsulated shell, everything changes. There are fewer drafts. There is less temperature stratification from the floor to the ceiling. There isn't as much of a temperature variation from room to room, regardless of whether each room has a heat source.

    If you build this kind of house, you will find that the ductless minisplit or ducted minisplit provides excellent comfort. If you use common sense when locating the unit or locating the registers, you won't notice any breezes and you will barely hear the thing operate.

  15. Richard McGrath | | #15

    Certainly Brad .

    This is the Phoenix Light Duty . There is a Big brother to this , Phoenix . Both can be purchased with a Solar Heat exchanger in 80 and 119 gallon respectively .
    http://www.htproducts.com/phoenixldwaterheater.html

    besides these there is the Versa Hydro available with the solar HX also .

    FPHX = Flat plate heat exchanger .

    If you are actually considering Mini Split options , there are water based options there also . Again I state , refrigerant options or requirements WILL again change and the possibility of you having to make a substantial investment to upgrade if a unit breaks or malfunctions in a system utilizing a heat pump water on one side will lessen that financial burden by at least not having to address the indoor units . This company has low wall options and in my opinion a better solution for high performance homes . The indoor units are very similar to the HTP stuff linked to earlier .
    http://www.chiltrix.com/

    Keeping refrigerant intrusion into the living space at a minimum promotes safer buildings . That is the intent of building codes after all , a safer built environment .

  16. Brad H | | #16

    What am I wanting? One option which I'm chasing down now, is all electric, avoid the monthly fixed fee for gas (which makes a little bit of gas expensive), as well as the installation & tap fee for gas (not sure if there is a tap fee yet). This also adds the potential to go net zero [added 4/8].
    If I'm going to install gas it gets relatively easy. I'd probably just get heat & DHW from gas, forget heat pumps or solar hydronic.
    I do have a desire for 'free' long hot showers once in a while :)
    I'll have some preliminary load calcs in a couple of days. In a previous lifetime (30 yrs ago), I was an HVAC engineer.
    Wife likes baseboard hot water. I should look at ducted (or not) mini splits a little more. Blowing hot air down from the ceiling doesn't seem like a good practice tho. But sometimes cost makes bad ideas work. Small, low mounted indoor units might get approval, but it's my understanding that you don't typically put one in each room, so that seems like a comfort downgrade from any other system.
    Dana, I totally agree that solar hydronic with heat pump will have more design risk, and more upfront cost.
    Richard, plz translate, ' Phoenix or Light Duty w/ SHX', 'FPHX' .

  17. Brad H | | #17

    I'm computing 22000 BTU/h for a load, with a design DT of 70F. This is using M Rosenbaum's spreadsheet & my own room by room. That's using an average R for the windows of 3.3, walls: 30, ceiling 60, slab 10. I need to work on the infil/ventilation numbers tho. Plan is very prelim right now.

    There are 2 spare bedrooms with loads of 1900 and 1200. I'll have to find the article here which discussed when heat was necessary, but I would think these would be chilly without heat in these rooms.

    Martin, You're saying that I could have a warm/hot air register at 8 or 9 ft, and there would be minimal stratification? I would think you'd need a fairly good air velocity to get the proper mixing and then you might have some drafts in the area. I'm still thinking about the mini-split option. They don't use them around here as far as I know, almost all gas furnace's.

  18. Expert Member
    Dana Dorsett | | #18

    Brad: A pair of Fujitsu 12RLFCDs has roughly that much capacity at -5F but there's no efficiency performance penalty for making that a pair of 18RLFCDs to give you some margin, since they both will modulate down to 3100 BTU/hr out @+47F.

    My in-laws recently mothballed the 50+ year old radiant ceilings in their recently purchased house over (well founded, as it turned out) anxieties about leaks, and replaced it with a right-sized modulating gas hot air furnace with ceiling registers. Most of the time you can't even tell the thing is running, and comfort levels are quite high. And that equipment has less of a modulation range that you'd have with a better class ducted mini-splits. It's a stark contrast with the old-school oversized scorched air approach.

    Their previous house had been heated with radiant floors in some parts, radiant ceilings in others. They absolutely know the difference, but were (very surprised to be) thrilled with the comfort level of their modulating ducted-air solution.

    BTW: A bedroom with a heat load of 1200 BTU/hr @ -5F would be heated entirely by a pair of sleeping humans at an outdoor temp of 40F. For the 1900BTU/hr room you'd need a coupla dogs too. :-) A ducted mini-split solution with a reasonable duct design can cover a handful of rooms without much difficulty, but even if you went with a ceiling-cassette point source solution it's not a crime to have an electric resistance heater to cover the times when you actually needed to bring those rooms up to temp when it's -5F out. A 500 watt panel convector + 1 human covers the 1900 BTU/hr load.

    Yes, R410A will be going away some day, but the notion that it's going to be an expensive proposition to re-charge with a different refrigerant or even replace the whole unit isn't well founded. The phase out of R22 took longer than the lifecycle of some equipment.

    There are already HFO1234_ _ variants that can be marketes as a drop-in replacement refrigerant in most R410A equipment:

    https://www.chemours.com/Refrigerants/en_US/products/Opteon/Stationary_Refrigeration/products/Opteon_XL55.html

    Wouldn't sweat that one too much. Even if it came to out & out replacement in 15 years (assuming R410A is completely banned by then, which is doubtful), the all-in hardware costs for a pair of 1.5 ton Fujitsu mini-duct unts is under $5K, a pair of 1-tonners about $4K. And in 15-25 years the replacement equipment is going to be substantially more efficient.

    If you went with a Chilltrix base solution, you'd either need a gia-normous buffer tank to coast through peak loads or you'd need two of them, if their capacity tables are to be believed:

    http://www.chiltrix.com/chiller-technology.html

    Playing the potential future costs game, natural gas pricing is extremely volatile, currently riding near historical lows, with nowhere to go but up. It's even conceivable that it would be burdened with a carbon tax within the lifecycle of the equipment. An all electric solution with sufficient PV to cover the power use could be viewed as an energy price inflation hedge.

    Richard: A Phoenix or Versa hydro based hydronic solution would be easy to design around, but it's not all electric.

    Only some, not all of HTP's equipment is made in MA. Major components (all of their heat exchangers) are often sourced elsewhere, even when the system is designed and assembled in MA. Some are 100% re-badged imports, eg: HTP's UFT series boilers are made entirely in Korea by the boiler manufacturer Kiturami, with most components manufactured in Korea using first-world quality control & tolerances rather than sourced from third party vendors in Vietnam or Malaysia to be assembled in Korea. Laars is importing some of the same series too. The series is called Homsys when it has the Kiturami name on it.

    http://gd.kidp.or.kr/eng/product/eng_product_view.asp?idx=19408

  19. Richard McGrath | | #19

    Dana ,

    Are you sure (all of their heat exchangers) are sourced elsewhere ? A very small percentage of HTPs products are imported . Parts , that's another ball game , there are very few manufacturers that don't use imported parts .

    There is a difference between the Laars boiler and the UFT , are you aware of what it is ?

    No , Phoenix and Versa Hydro are not all electric nor does any of the heat energy come from electric . What has that to do with this discussion , this man never stated he wanted all electric , instead he asked what might be best in his home . He did state that he wanted a hydronic solution , does Fujitsu , Mitsubishi or the like have a product that is a hydronic solution ?

    Just trying to help this gentleman make an informed decision . Ease of design is not something I struggle with , I can design for many different fuel choices and come up with the best solution taking into consideration someone's wants and needs . You folks just seem to have a single solution for every situation . I can tell you that some folks don't spend what they spend on the envelope so they can throw comfort out the window or tolerate certain things based only on first cost . By the way COMFORT is not an air temp . T db is not a proxy for thermal comfort quality , there are actually 12 more .

  20. GBA Editor
    Martin Holladay | | #20

    Richard McGrath wrote, "Phoenix and Versa Hydro are not all electric, nor does any of the heat energy come from electric. What has that to do with this discussion? This man never stated he wanted all electric. Instead he asked what might be best in his home."

    Brad Haack (the original poster) wrote (in Comment #14), "One option which I'm chasing down now, is all electric, avoid the monthly fixed fee for gas."

  21. Brad H | | #21

    Why 2 minisplits instead of 1 larger heatpump & zoned air handler?

  22. Expert Member
    Dana Dorsett | | #22

    Even modulating ducted heat pumps have turn-down ratios less than 3:1, some less than 2:1. (The Carrier GreenSpeed series are about 2.5:1, and they crow about that in their advertising.)

    Most ducted heat pumps have lousy cold climate capacity & efficiency, and poor defrost control.

    Using zone valves in the ducts unbalances the duct system (always), which dramatically increases room to room pressure differences, and those pressure differences drive outdoor air infiltration whenever the air handler is operating, and it's worse when driving a single zone.

    Mini-splits are have much bigger turn down ratios, and at the lower end of their range (where they spend most of their time) deliver phenomenally good efficiency. The aforementioned Fujitsu _ _ RLFCD series mini-ducted mini-splits can drop back to 3100 BTU/hr @ +47F. The 12RLFCD can deliver 3,100~19,400BTU/hr @ +47F more than a 6:1 turn down, and the 18RLFCD delivers 3,100~25,600BTU/hr @ +47F, which is more than an 8:1 turn down.

    http://www.fujitsugeneral.com/PDF_06/Submittals/12RLFCD%20Submittal.pdf

    http://www.fujitsugeneral.com/PDF_06/Submittals/18RLFCD%20Submittal.pdf

    Both the maximum capacity and the ratios shrink a bit with outdoor temperature, and you'll have to consult the extended capacity tables to be sure to size them for the zone loads. The 18RLFCD is the biggest in that series, and you really need to assess the load calculations carefully agaist the capacity tables when committing to just one.

    Richard: I may be mistaken, on HTP's heat exchangers, but my understanding was that they were all outsourced. The Laars-FT badged Kiturami units are combis, identical to HTP's EFT wall hung and floor mount combis. Compare the pictures of their innards:

    http://www.htproducts.com/EFT_Combination_Wall.html

    http://www.htproducts.com/EFT_Combination_Floor.html

    http://www.laars.com/product/mascot-ft.aspx

    True, comfort is not an air temperature, but in a "pretty good house" level of building performance they come pretty close to being the same thing. With high-R houses that have high performance windows the average radiant temperature of any surface isn't very different from the room air temperature. At PassiveHouse levels it's even closer.

  23. Stephen Sheehy | | #23

    Brad: I've found that for the most part, just one minisplit has kept my zone 6 house comfortable, but in the middle of the winter we'd keep both on during the day. It depends on layout to some extent. Our architect recomended we install two, especially for A/C on the occasional hot day.

    With a tight house, statification isn't an issue with a single minisplit high on a wall. Ductless units are more efficient than ducted systems.

  24. Expert Member
    Dana Dorsett | | #24

    By the bench tested HSPF numbers ductless mini-splits are more efficient than ducted minisplits, but that's only half the story. How you mount and operate them matters.

    Ductless heads mounted near the ceiling are pulling in air a few degrees warmer than specified in an HSPF test. That increases difference between indoor & outdoor air temp, which decreases efficiency. Then, if you need to keep the room with the ductless head 5F warmer to keep the rooms without heads comfortable it's an even bigger hit.

    A ducted mini-split with the return registers at or near the floor would be pulling in cooler air, which increases both the efficiency & capacity a bit.

    As rule, if ductless, using a floor-mount version will have a heating season efficiency edge out of a wall coil mounted near the ceiling using the same outdoor compressor, even if the HSPF test numbers are the same. The wall-coil types would have a cooling season efficiency & capacity advantage at the same bench tested SEER.

    Done well you can probably beat a ducted mini-split on overall efficiency. Uxorial objection to the visual aesthetics of ductless heads was the reason for embarking on the ducted mini-split discussion.

  25. Reid Baldwin | | #25

    I had to look up uxorial. Merriam Webster says "of, relating to, or characteristic of a wife." Thanks Dana for increasing my vocabulary.

  26. Expert Member
    Dana Dorsett | | #26

    Reid- From the latin "uxor" (= "wife") At least I didn't make that one up- I must have been in a Latinate mood. :-)

    Don't encourage me too much on vocabulary- it can get out of hand. A couple of weeks ago on a skiing list-serve forum I let loose an arabi-norsk chimera into the world, "inshullr", derived from the Arabic "inshallah" (= god willing") and the Old Norse "Ullr" (= the name of a skiing god: https://en.wikipedia.org/wiki/Ullr ) Even worse, the word that followed was the Algonquian word "wachusett" meaning "near the mountain", but has been taken as a geographical name in central MA. Strangely, the meaning of "inshullr" was in fact understood by the fairly narrow audience, but out of context it's obscure stuff- it's not even in the Oxford English Dictionary (yet! :-) ) .

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