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Stupid Heat Questions

spinnm | Posted in Energy, Heating & Insulation on December 5, 2003 09:22am

Here’s the deal.  I’ve promised to build a house for a friend.  Here, in the land of concrete slabs, RIF heat is the norm in the upper end.  She keeps her house quite cold and is leery of the lag time to alter the temps in case of company.  Good point.  So, my questions are these:

Surely there are CFA systems that are quiet, filtered and don’t throw a lot of dust around.  Would you, who deal with them, suggest some that are satisfactory?

Then, I was thinking, that the RIF heat systems that are used with wood sub-floors would probably be more like the baseboard systems of old….the lag time to alter the temps in the house would be less.  She’s talking about hardwood floors.  So…..have any of you actually used the tubing/subfloor systems that are advertised in FHB?  Problems with the wood twisting or cupping?

I haven’t seen a wood sub-floor house around here that’s less than 40 yrs old.  I’m swimming upstream.  But, if she wants wood floors my inclination is to not use the pre-finished, can’t-be-refinished, veneer floors that are common today.  Am I wrong?

ShelleyinNM

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  1. User avater
    CapnMac | Dec 05, 2003 09:36am | #1

    Since you are looking at most of the house for the change, you are going to be dealing with a floor elevation change, no matter what.

    One approach would be to lay out radian heat o nthe floor, and float in new concrete over that.  Adding prefinished wood over that only adds another 1/4 0r 3/8 to that depth.

    To add "real" wood floors & radiant heat, you will need sleepers & such to make the space, and to propery support the new floor.  Going to be about the same elevation change.

    Why is the elevation important?  In a word:  Doors.  Doors also means trim, but that's going to get swept up in the all new baseboard work for the floors.

    My inclination would be to add "real" wood, but I also take a long-term view of these things.  But I alos like the character of a wood floor (including squeaks, dips, & waves <g>).

    Occupational hazard of my occupation not being around (sorry Bubba)
    1. darrel | Dec 05, 2003 09:41am | #2

      How often does she have guests on short notice?

      What if you just stuck with RIF and then added an electric baseboard or one of those heated ceiling fans for the guest bedroom?

    2. reinvent | Dec 05, 2003 03:35pm | #3

      Dude he said he is building a house. I think elevation can be what ever he wants. Starting from sratch. Not trying to bust your **** just trying to clarify(assuming I am correct in my interpitation) So with that in mind what would you do?

      1. spinnm | Dec 05, 2003 05:24pm | #4

        Right.  It's an air house right now.  I'm going to use CFA unless someone here tells me that RIH acts like I think it will with wood, has used the system, and declares it satisfactory.

        If CFA I know that people around here have favorites.  Looking for suggestions since I've not used CFA since 1990.

        Won't use ele baseboard.  Ele rates too high.  Makes the meter spin.  She doesn't like the look of baseboard....gas or ele.

        ShelleyinNM

        1. darrel | Dec 05, 2003 05:38pm | #5

          How about the ceiling fan units? (I honestly don't know anything about them other than that they exist) I understand electricity would be expensive, but if it's just to warm up a room once in a while until the RIF catches up, it might make the best of both worlds.

          That or just have her keep some extra sweaters by the front door ;o)

      2. User avater
        CapnMac | Dec 06, 2003 01:14am | #13

        So with that in mind what would you do?

        First, I put i nthe clutch and take it out of remodel gear <g>.

        Having read the rest of the posts, Cloud, Dave, & csnow have all expressed what I would.  I'd make an arguement that building a propper wood floor would add value and uniqueness to the house--and has some efficiency bonuses in NM, too.

        But, I like wood floors.  And creaky old home with character.Occupational hazard of my occupation not being around (sorry Bubba)

  2. User avater
    Mongo | Dec 05, 2003 07:25pm | #6

    Low mass RFH will give you a fairly quick response time. Detailing it to be on top of the slab will work.

    Low-mass is very common for sleeping quarters. The person can keep the room a little warmer during the day a little cooler at night.

  3. blackcloud | Dec 05, 2003 07:39pm | #7

    If you are looking at faster response times than you should consider something like the Stadler Climate panels, they have a much faster reaction time than a slab.  Down side is they cool down faster but in your case this sounds like just the ticket.  As far as the wood floors I used a prefinished 3/4" thick hickory/Pecan as it is fairly stable and had a fantastic look to it.  An advantage to using a prefinish is that it has micro beveled edges which do not show the cracks as the floor expands and contracts from moisture and heat.  Also look at engineered flooring (not the cheap stuff) use something like Mirage, it has the same amount of material above the tongue as tradition flooring yet it is far more stable.

    Jason

    If it wasn't for bad luck I wouldn't have Any!
  4. Foamer | Dec 05, 2003 08:04pm | #8

    I am considering RIF for a remodel of my house and share your concerns about flooring materials. However, there is a solution. Put the heating tubes in the ceiling using aluminum heat distribution panels on 1x. Install drywall in contact with panels. Presto, quick reaction time due to low thermal mass of gipsum and no limitations on floor coverings. The temperature gradiant in the room will be slightly less ideal but only marginally so. The beauty of radiant is that it heats the things in the room, including the floor in this case. I spoke to a couple of radiant manufacturers who okayed the idea.

    1. User avater
      Mongo | Dec 06, 2003 08:02am | #16

      Ceilings are a viable installation. As are walls. Depends on the room, though.

      1. Foamer | Dec 08, 2003 06:12am | #17

        Hi Mongo,

        Do you have any tips for ceiling installation? Sounds like you have tried it.

        Torsten

        1. User avater
          Mongo | Dec 08, 2003 07:03am | #18

          Torsten,

          Ceilings...not that they're necessarily trickier, but in some ways they can be. The heating is diffrent, so it's not quite as comfortable as floor heating would be.

          When compared to flooring, there is only drywall between the tubing and the living space, so there it little resistance to heat transfer.

          Unlike flooring, with ceilings the whole veiling usually doesn't need tubing. If not, run it against exterior walls, working in to the inside walls. Often times the amount of tubing in a floor can exceed the BTU requirement that is needed, and you can get away with it. Ceilings can be more finicky. Design them closer to the load requirements.

          It's very much a low mass system, thus it has the benefits (quick response time) and the drawbacks (poor heat retention). Thus, it's good for bedrooms where you may have the desire for a several-degree temp swing during the day. Also, bedrooms can be cluttered with large-footprint furniture which can result in warmer flooring temps under the bed, etc. What's on the ceilings? Not much to block the heat, that's for sure. It's also good as an auxiliary heat source. For example, a room with large amounts of glazing in a cold climate. RFH alone may not ba able to handle the BTU requirements. Add a bit of ceilign heat along the glazed walls and youre in business.

          Installation? Insulate the ceiling bays as required. Build down your electrical ceiling boxes, as well as air conditioning outlets, is applicable. I prefer to then tack 1" polyiso to the rafters. Gap the sheets by about 1/4", then use canned foam to seal the gaps. You should now have a tight ceiling.

          Run furring strips. Furr the ceiling, perpendicular to the rafters, screwing through the furring strip, through the polyiso, and into the rafter.

          The design will specify how close the tubing runs neet o be to each other...close together for concentrated or spaced further apart for more even heat distribution.

          Typically, you'll have only one wing of the al plate stapled to a furring strip, with the plate's channel and PEX in between the furring strips. The other wing of the Al plate will "float" on the adjacent furring strip so that it can freely move as required. The adjacent furring strip will suport the second wing (the second wing will be sandwiched between the adjacent furring strip and the eventual drywall). Adjacent Al plates should not touch each other.

          Drywall gets screwed to the furring strips.

          Have the heat off when taping and mudding the ceiling drywall.

          Hope that helps!

  5. csnow | Dec 05, 2003 08:27pm | #9

    Once saw a 'thin slab over thick slab' design to minimize radiant mass.

    Basically, the structural slab was poured, covered with insulation, thin slab with imbedded tubing poured over that.  I bit unusual, but should work.

    Find out why your friend likes it cold.  With radiant, normal air temps run cooler and it is more comfortable to breath.

    In an Air scenario where the heat is cranked up, the thermal mass of the cold slab works against you.  Cold feet, hot head...  Not comfortable.

    1. User avater
      CloudHidden | Dec 05, 2003 10:10pm | #11

      I'm with Mongo and csnow. First, find out why she likes it cold, and how cold. If it's be/c she's used to warm air blowing around her head and doesn't like that, that can be avoided. If it's be/c she's just cold-blooded, then the low-mass RFH solutions are good. They'll be responsive. Thinking of Warmboard and its equivalents. Depending on the answers to the "how cold" question, a regular slab could also work fine. It doesn't take that long to raise the temp in a 4" slab. The one scenario to avoid is a hi-mass, poorly insulated house. That's a combo that would be hard to control with regards to fluctuating outside temps.

      1. DavidThomas | Dec 06, 2003 12:49am | #12

        You can also mix and match, it's not an either/or situation.  My house was totally high-mass RFH.  Worked fine to keep it always 70F inside but didn't respond quicky when outside temps dropped from 15F to -25F overnight as they sometimes do.  Wake up to 66F house and it would take a while to catch up.

        Shoot-from-the-hip design:  RFH off thermostats set for her body.  You will have a hot water source and pumps and controllers for that.  Also do a zone to kick-space heaters under the cabinets or what-not.  (Take that water off BEFORE the tempering valve).  Run off another t-stat for the F/A.  An hour before the party, turn up the second t-stat which is normally off.  The mini forced air comes on and boosts the temps (to 71F?).  The RFH is continuing to carry the baseload (to 67F?).  The F/A component can be quite small because it never acts alone.  Only as an adjunct to the RFH.

        I usually turn the heat DOWN before a party.  Each human puts out about 300 watts.   15 people is like running 3 hair dryers on high.  Vastly more if they are dancing.David Thomas   Overlooking Cook Inlet in Kenai, Alaska

        1. User avater
          CloudHidden | Dec 06, 2003 02:18am | #14

          >The mini forced air

          We had a mini-duct forced air for that very kind of thing. But our volume of air space was such that it never seemed to do anything we could feel. So we just put all energy into the rfh and that keeps things good and constant. But a traditional house will have less excess volume and your idea should work well, of course.

          1. DavidThomas | Dec 06, 2003 02:20am | #15

            "But our volume of air space"

            When you build big, concrete bubbles. . . .    :-)

            But radio-controlled model planes becomes a viable indoor sport!David Thomas   Overlooking Cook Inlet in Kenai, Alaska

  6. fortdh | Dec 05, 2003 08:46pm | #10

    There are some excellent forced air systems out there; design and installation are very important. Some variable speed blowers in the air handlers can be very quiet as they do most of their work in the lower settings, and only go to high speed after 7-8 minutes. I like air movement and filtration, and suggest high/low return air grilles with pleated filters in each grille.

    If building for myself today, I would use both forced air (A/C a necessary) and rad floor heat in certain locations, such as all tile areas, breakfast room, den and where ever the desk/computer sits. LR, Dr,kit,and bedrooms can remain FA for my likes.(baths would also have both, as I want the humidity dispersed in the winter)

    I would also use a properly sized high efficiency gas water heaters for my heat source and domestic water; a water coil heat exchanger in the air handler for the FA heat, and RF loops for the room coils. I would rec two water heaters so that operating on one would still be adequate to keep the house from freezing if one heater failed.

    I would like to hear from some on this forum re recommended RFH manufacturers, and who to avoid. Hope this is helpful. Paul

    Energy Consultant and author of Practical Energy Cost Reduction for the Home

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