Plates question

Wayco Wayne_2

I was surfing the net last night and came upon a site about radiant floors and underfloor systems. This site recommended using the thin flashing thickness plates and using a 2 inch air gap beneath it like staple up, tubing only systems. I've never used the thin plates, always the thick thermofin or Joist trak plates and with those I have always been told to push the insulation up against the plates and floor, no air gap. The reasoning being is that these thicker plates were injecting the heat directly into the floor and not heating the air space like staple up tubing only systems. Was this site correct in it's recommendations for the air gap with thin plates? Are the thin plates used differently than the thick plates, and are they used to warm the air in an air gap instead of into the floor? I honestly don't know but it sounds suspect to me. WW

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Andrew Hagen (ALH)

Hard to say

but I'd guess the 2" is something that got held over from suspended tube systems. There's really no magic 2" number when you're conducting. Foil backed insulation isn't going to do much good when pressed up against the tube. Foil backed bubble wrap may be reduced to almost nothing if pressed up against the tubes.

I'd say the primary benefit of the thin plates is that they keep a more constant contact between the tube and the floor. No doubt the aluminum does something. I think it's .025" thickness which is half that of ThinFin or Joist Track. Thermofin original is .0625" thick.

Limitations on the heavier plates are primarily based on what can physically be extruded. The snap fit of the extruded plates is a major advantage over thin plates, and the fit has to be very tight. The snap fit is really THE advantage extruded plates have. Any gap really does show up, even with a simple radiant thermometer.

That being said, omega plates are better than suspended tube or traditional staple-up. There may be noise issues due to the lack of a tight grip on the tube, unless it's so loose that the tube moves freely. But then pex-al-pex helps with that.

it's really the tube-plate interface that creates the bottleneck. Omega plates ignore that for the most part. Plus the labor can't be much different for omega plates versius extruded plates....and that labor is significant. In general I'd say it's like stepping over a dollar to pick up 75 cents.

At least that's how I see it....

-Andrew

Bob Gagnon plumbing and heating

a rep from rehau

told us they want 2" air space under plates, and he acknowledged that other manufactures call for the insulation up tight to the plates. Bob

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Wayco Wayne_2

Yikes!

This rocks my world a bit. Did he seem to know what he was talking about?? Rehau is a big name. You gotta consider that they know what they're doing.

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cruizer

Depenging on the plate size, the reason some manufacturers say to put a small 2" air gap is to help create an even heated surface across the floors. There is a gap between the some manufacturers plates, and although it is very minimal, it can create a striping effect, especially over the joist. Because it is only a 2" gap, it doesn't take long for the air space to heat up. It is not detrement to the heating system, but more for the comfort. The plates are still forcing most of the heat in the upwards direction, and still maintaining an overall system temperature that is lower than a no plate system.

Bob Gagnon plumbing and heating

he seemed to know

he was giving a quick overview on radiant heating, in a solar heating class. I have a staple up job where they pushed the fiberglass up to the pex and subfloor and that job works fine. Bob

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Wayco Wayne_2

It makes sense I guess

the plates will still inject the heat into the sub floor but add an air space and the heat will even out by heating the air in the gap. In the end more materials and labor for how much benefit? Is the striping that noticable? Is it worth it? Creating an air gap takes time and energy. Inquiring minds want tot know. WW

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Unknown

FWIW, we did lightweight plate jobs for many, many years advising people to put the insulation all the way up before anyone ever thought of using a small airspace there with plates, and we have never had a callback for heat striping.

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My past few jobs

have been spray foamed against the plates. I haven't noticed any issues with striping.

Constant circ really evens out floor temperature. And on the other extreme is a bang bang temperature and flow control with high temperatures.

Floor coverings, more than anything, seem to make a difference in noticable striping. Plates below the plywood better than onn top, tile right over a subfloor is the worse, any additional layers between the plates and the final covering spreads the heat better. Even a layer of cement backer board helps. Throw rugs really even out the temperatures, but of course reduce the output by the R value of the covering.

I think Dale has some ThermoFin isotherms that show this very well. Siggy has done some FEA models of this also.

hot rod

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