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Radiant Details

Patrick Greenwood | Posted in Mechanicals on

I’m in 5A

What experiences have people had putting PEX in the ceiling of the space to be heated by hydronic radiant? In other words, PEX in the basement slab and PEX in the main floor ceiling of a ranch without walkout basement?

What experiences have people had with radiant cooling from the ceiling vs. from the floor? Is one overwhelmingly better than the other, or is it a toss-up? Everybody I talk to here says I must resign myself to a full-blown full-size duct forced-air AC system for cooling. Maybe that’s so, but I’d like to here from the enlightened crowd here.

Winter humidification? How would you handle? Is there a better solution than central steam humidification?

Finally, How much difference do staple-up aluminum plates (like the 24″ x 5″ heavy flashing size with a groove to accept PEX) really make? My sense is their additional cost isn’t justified by the slightly higher water temp required. It seems foil-faced batts would reduce back-loss equally well and also deaden sound (if installed below PEX in the floor of the main floor.

Forgive me if these questions have already been answered.

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Replies

  1. Paul Brazelton | | #1

    I have pretty much what you're talking about (sans the PEX in slab), so here's my experience from four heating seasons in Zone 6B:

    * I'm sure radiant cooling is not totally useless everywhere, but here in MN it's pretty much that. From the floor is marginal, as it can keep the floor cooler than air temp. I can't see from ceiling doing anything at all. The math just doesn't work out - the amount of water you'd have to push through a system to cool a house substantially would be incredible.

    * I use a 5 gallon Kenmore humidifier on the main floor to keep the house @ 40%. With a fairly tight house, I have to refill it just a few times a season, and it's quiet. I've read here that you can even put something like that in a closet, if it offends your sense of aesthetics.

    * I have segments have have just staple up plates, just a radiant (foil) barrier under the tubing, and both. Mostly both. They both make some difference, but the staple up plates make a huge difference. If I ever do this project again, I'll probably even pony up for the heavier extruded plates, as these really make the floor an effective heater.

    * Sound deadening of fiberglass is pretty minimal. I ended up using recycled denim batts, and they provide more (though not a lot) of sound insulation.

  2. GBA Editor
    Martin Holladay | | #2

    Patrick,
    Q. "What experiences have people had putting PEX in the ceiling of the space to be heated by hydronic radiant? In other words, PEX in the basement slab and PEX in the main floor ceiling of a ranch without walkout basement?"

    A. Radiant ceilings or radiant walls can work well for providing heat, especially if the home is tight and well insulated.

    Q. "What experiences have people had with radiant cooling from the ceiling vs. from the floor?"

    A. Radiant cooling almost never makes sense, because of the problem of condensation. If you cool your floor or ceiling enough to cool your house, the entire floor or ceiling will become a condensing surface. In the case of a ceiling, it will drip like a bat cave.

    Q. "Everybody I talk to here says I must resign myself to a full-blown full-size duct forced-air AC system for cooling."

    A. If you don't like ducts, you can always install a ductless minisplit unit.

    Q. "Winter humidification?"

    A. Don't do it. Winter humidification is only necessary in a leaky house. If your house is dry in the winter, find the air leaks in your envelope and seal them.

  3. Paul Brazelton | | #3

    Martin, regarding humidification:

    What is the downside to maintaining a certain level of humidity? I agree that if we were to keep our house completely sealed all winter, it would be a non issue. However, we do occasionally use our fireplace, which brings in a huge amount of cold, dry air (I know, I know, but my wife likes it). It can take days for the humidity in the house to rise out of nosebleed territory. We also have whole months in MN that never rise above freezing - a tight house does not magically create moist makeup air when we're running our dryer and other forms of exhaust venting throughout that time.

  4. GBA Editor
    Martin Holladay | | #4

    Paul,
    Used cautiously in a house like the one you describe, a humidifier probably won't cause any problems.

    However, if 4 homeowners have humidifiers, 3 of them use them properly, and the fourth just about destroys the home by raising the humidity to the point where condensation and mold become big problems.

    If at all possible, I advise people to stay away from humidifiers.

  5. John Klingel | | #5

    Pat: I'd suggest you buy John Siegenthaler's book "Modern Hydronic Heating". You'll find a wealth of information there, and it may change you mind on the heat distribution plates. From what I read there and other places, using them is well worth it. He also discusses radiant in ceilings and walls. john

  6. Patrick Greenwood | | #6

    John -- I haven't heard of this. I'll definitely check it out. Thanks!

  7. Expert Member
    Akos | | #7

    Patrick,

    Heat plates make a big difference. I ended up adding a bunch to a kitchen area to increase the floor temperature over a staple up setup. On one project I used the clip on heat fins (Ultra Fin) which are significantly easier to put up than heat plates and work just as well. No matter which system you go with a layer of insulation underneath is a must (the cheapest batt insulation you can find will work the best).

    Akos

    1. Expert Member
      Dana Dorsett | | #8

      You realize that Patrick posted that nearly 8 years ago, right?

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