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Old 11-01-2008, 06:45 PM   #1
drh
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Radiant floor under two layers of subfloor = ok ?


Quick question to all you radiant floor people.

I'm in the process of installing (staple up) radiant PEX piping under a sunroom (which is over a garage) which has two layers of wood (about 2" thick altogether). I have installed a reflective foil beneath the pipes to help reflect the heat up, and will be spray foaming 4" (R30) beneath that.

My question is, even with two layers of subloor beneath the engineered hardwood on top, will the heat still reach up through the boards? I'm assuming with the reflective insulation + spray foam beneath, the heat has nowhwere to go but up, but I thought I'd be sure.

Thanks!
Dan in Canada

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Old 11-01-2008, 08:30 PM   #2
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Radiant floor under two layers of subfloor = ok ?


You should be fine.

Remember that there is a lag time (I call it latency) between the heat going in and the heat getting to you from the floor. Once the floor is warm it will stay warm for a long time so the heat will be pretty even. With your extra wood that you have it will take longer to get warm but also will take a lot longer to cool down.

Did you install the heat panels on the pex or is it just the pex alone?

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Old 11-01-2008, 08:39 PM   #3
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Radiant floor under two layers of subfloor = ok ?


Thanks for the response, Marvin.

I installed the aluminum heat transfer plates (from Rehau), on each run, spaced about 3" apart from one another, and left approximately 1/2" to an 1" air gap between the insulation and subfloor above.

Once everything is insulated, I'm also guessing there may be some latency before the heat reaches the room, but the benefit with extra layers is that the "mass" will hold the heat longer.

Cheers,
Dan
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Old 11-01-2008, 09:10 PM   #4
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Radiant floor under two layers of subfloor = ok ?


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Thanks for the response, Marvin.

I installed the aluminum heat transfer plates (from Rehau), on each run, spaced about 3" apart from one another, and left approximately 1/2" to an 1" air gap between the insulation and subfloor above.

Once everything is insulated, I'm also guessing there may be some latency before the heat reaches the room, but the benefit with extra layers is that the "mass" will hold the heat longer.

Cheers,
Dan
Sounds like you are good to go.

Once your floor heats up you will really enjoy the heat. And the efficiency.

The plates can go right up against the floor if you want to.
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Old 11-02-2008, 06:43 AM   #5
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Radiant floor under two layers of subfloor = ok ?


With the spray foam.
You may be ok.

The plates attached to the sub floor would transfer heat better.

With flooring that thick, it may not meet set temp near design conditions.
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Old 11-02-2008, 09:42 AM   #6
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Radiant floor under two layers of subfloor = ok ?


Her comes Been and his Dream Killing pin! Get a great idea and he comes along and pops your balloon with some little detail, no matter how small, that would make the job just a little better!

ROFLA!!!
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Old 11-02-2008, 09:57 AM   #7
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Radiant floor under two layers of subfloor = ok ?


LOL..

People get testy when its 0F outside, and they can't maintain set point.

Then they use expressions most forums won't allow to be posted.
And include humorus thigs things like.
" I spent xxxx thousands of dollars, and its not heating right".
" The other guy said it would @?*&^ work".
" But he won't @?*&^ come back anymore".

There are advantages to being a pestimistic optomist.
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Old 11-02-2008, 10:34 AM   #8
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Radiant floor under two layers of subfloor = ok ?


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There are advantages to being a pestimistic optomist.
It's all terminology. I call that a realist. Someone who believes in the Law of Unintended Consequences.

I thought of installing the plates on the floor also but he is going to have R30 foam insulation. I mean who has R30 on the floor??? His heat isn't going anywhere but into the floor.

I just figure that the latency will be a little longer but not that much to make a difference on a 2" floor. Once that puppy gets heated up it will be April before it cools off.
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Old 11-02-2008, 01:27 PM   #9
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Radiant floor under two layers of subfloor = ok ?


We'll see how well it does, after its in, and he has had a couple days at design temp.

The Pex heat transfer rate drops the warmer he has to heat the cavity air to heat the wood flooring.

By fastening th plates to the floor, he increases his transfer rate.

With R30 insulation, he may have minimized his heat loss enough it doesn't matter.

But, I sure wouldn't want to take that risk, with a ceiling I can't easily open and close again later.
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Old 11-02-2008, 01:27 PM   #10
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Radiant floor under two layers of subfloor = ok ?


The insulatation below the radiant should be 6 times the "R" value of the floor above the tubing.
If needed you can change the water temp or the flow through the tubing to increase heat output.

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