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Air conditioning house with radiant floor heat

Salesi | Posted in General Questions on

Does anyone have an energy efficient cost effective way to air condition a house with radiant floor heat. We are currently in the building phase of our house which I hope to make as air tight as possible. I was considering the typical HVAC system until my curiosity was sparked by installation of a radiant floor heating system. However do I need to put in conventional ductwork with an air handler for the air conditioning system? Mini splits are one option I guess, however I am working within a budget. I am hoping there is a cost effective way to have both in floor heating and air conditioning. If anyone has experience along these lines, please me know what you did for A/C. Thanks.

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    The only way to narrow in on what make sense is to start with the actual cooling loads. Try running room-by-room load numbers using a cheapie/freebie Manual-J-ish online tool such as loadcalc.net or coolcalc.com.

    Be aggressive rather than conservative in your inputs or you'll oversize by quite a bit. (With LoadCalc I always assume hermetically sealed air tight house with no ventilation and zero duct leakage, and it still comes up with bigger numbers than a pro tool.)

    With room by room load numbers scribbled on to a sketch of the floor plan it's possible to make reasonable recommendations. Without the load numbers it's like asking "what would make a cost effective car", and the answers will be quite different for a single person commuting 30 miles/day vs. a family with 4 kids and two dogs that spend weekends driving over a hundred miles between soccer games with the travel teams and dog shows.

    1. Salesi | | #4

      Ok, let's say I have the room by room heating loads and cooling loads. With a radiant floor heating system, I can size it just right for what I need. But I cannot use the radiant floor heating system for the cooling loads. Therefore I would need to install a different system for the A/C. The question is if I already have a radiant heating system, what is the energy efficient, cost effective way to provide A/C without breaking the bank. If I need to install an air handler, ductwork to all the rooms, and an outside condensing unit for A/C, I might as well delete the radiant heating system and put in a typical forced air furnace and a/c unit. I am attempting to balance the best heating and cooling systems and my construction budget. I like the idea of warm floors to heat the house that radiant heat provides.

  2. Jon_R | | #2

    You can also provide cooling with fan coils. Or, with dehumidification, radiant cooling.

    > a house with radiant floor heat

    Consider putting the radiant tubing only in places where you walk/sit. This will make those floor areas warmer, closer to the "warm floors" of yesteryear. Without doing this, I wouldn't bother with radiant.

    Do you have a crawlspace? If so, over-heating it a little can provide warmer floors at minimal cost.

    1. Expert Member
      Dana Dorsett | | #3

      I would assume (perhaps incorrectly) that a house "...currently in the building phase..." might have the radiant floor details already baked in the cake.

      If not, it's time to take a step back and run the load numbers (or have an engineer, not an HVAC installer run them) to see what really makes sense.

      1. Salesi | | #6

        Radiant floor is not "baked in the cake". Funny story on the load numbers. I had them run by an engineer not an HVAC company. I went to three HVAC companies in the area for quotes. A small, medium and a large (read expensive) outfit. Not one of them wanted the load numbers for the house or how it was to be insulated or anything. I though why did I pay to have the heating and cooling load numbers if they are not going to be used for sizing the HVAC system.

        1. Jon_R | | #10

          Casual estimating and the resulting over-sizing usually produces good enough efficiency and comfort. So these places remain in business without excessive complaints. Agreed, you might get a different impression from this forum.

  3. walta100 | | #5

    I am sorry but radiant floor heating with AC is not part of a budget build, it is part of a money is no object build. Just because you will have 2 separate mechanical system more than doubling HVAC budget.

    A few mini split heads will cost less than AC and a full duct system. My guess is you will get a bids for a mini head in every room with a capacity of 3 times the AC they will bid.

    Walta

  4. GeneDJ | | #7

    I don't have personal experience, but I recently came across the CHILTRIX.COM high efficiency heat pump. The components look like a mini-split, but the refrigerant is confined to the outdoor unit, and heat is transported by a water/glycol loop to the indoor units. One of those "indoor units" could be your radiant floor loop (instead of a boiler). In the summer it can also be used to cool the floor. You will need one or two wall mounted fan-coils in order to keep the humidity low enough so that no condensation occurs on the floor (air dew point < floor temp). But much of the sensible cooling will be done by the radiant floor. Because the refrigerant is confined to the outdoor unit, the system can be installed by your plumber or you if you are self-building. It can also be used to heat domestic hot water. They have many system diagrams on their web site.

  5. this_page_left_blank | | #8

    Given the existence of heat pumps, radiant in floor heating makes zero sense for any house with any cooling load. Ask me how I know. We actually thought we'd be able to get by without cooling, otherwise maybe we wouldn't have made this mistake.

  6. MonzaRacer | | #9

    Actually considering that you have your heat figured out with your radiant floor heating two more or less keep your feet warm which in most places is about 60% once you have the sealed house up to temp I've been looking at a product called a MRCOOLDIY mini splits, AND these are supposedly considered heat and cool but mostly cooling in my opinion from the design. But supposedly they are actually owner installable and you can get different sizes and they come pre-charged you don't have to have an HV AC installer come in and do major work you have the external unit that you place outside and then you have 25 foot of connections that you run through the wall out to the unit and I assume that you only have to run one wire to the head unit that hangs on the wall however that's done I haven't actually done the looking at the actual installation but that's my theory, but from the head unit to the outside unit looks to be fairly simple. And the fact that if they are owner installable with a very good warranty and returnable if you suspect them properly I was actually impressed when I read about these things considering the fact that I'm not that big of a fan of a heat pump in the conventional sense where you have to have the big unit outside and all the buried stuff under the ground because the area where I live is all clay which makes installing anything in the ground a major pain in the back side. Just give them a check at mrCoolDIY.com.
    Maybe these can help you out but Just a thought.

  7. STEPHEN SHEEHY | | #11

    If budget is an issue, don't do in floor heat. For that matter, if comfort is an issue, don't do in floor heat. Spend your money on insulation and air sealing and use a couple of minisplits. Listen to Trevor Lambert.

  8. Kenny78 | | #12

    On the chiltrix mentioned, there is a thread on here that has a couple real world experiences. While it could be the best thing out there in time, the product does not seem reliable or foolproof enough unless you are a tinkerer. I find the product fascinating and had to really talk myself out of their system for our upcoming build.

    I would also recommend against the mrcooldiy or other lower tier minisplits. Unknown but I assume you are in a heating dominated climate. If so, Fujitsu and Mitsubishi have good options that maintain output

  9. GeneDJ | | #13

    Re reliability: I think the Chiltrix should be more reliable than any m ini-split simply because it is a self contained refrigeration system (not split & joined in the field ). Moreover it is built from top quality components. What I am unsure of is the seasonal winter performance. They give a lot of info about part-load cooling performance but only a single COP number for heating. I want to know part-load heating performance for cold winters.
    With that said, I agree with the comments saying if you insulate the home shell really well you should have bare foot comfort with just the fan coils & no radiant. But note that Chiltrix can heat a domestic hot water tank which mini splits don’t do & if you don’t have a basement for a heat pump water heater there are no efficient non-fossil options, other than the expensive Sanden unit.

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