Are heat transfer plates absolutely necessary for staple up?

hot_rod

would be my choice and they need to touch the floor tightly to leverage the conduction transfer. They work great with spray foam.

I doubt you could spray foam around suspended tube without seriously limiting the convective currents?

Nails shouldn't be a problem later if the installer knows tube is installed below the floor. this is commonly done without a problem.

hot rod

bruce_21

Hello ALL,
The situation is this: A staple up radiant below plywood subfloor. Finish floor of some sort of hardwood to be installed "when HO has the $$ to do it" for now he will just paint the plywood. So to preserve the PEX from later nails I'm thinking it wise to attach it to little pieces of plywood or 1x so it will be down 3/4" below and safe from nails, especially since there will be 8 inches of spray foam insulation below the tubing-- a leak might take a long time to show up and then there'd still be no way to find it. But then what good are the heat plates? Will they still do anything if not in contact with the subfloor. Also should the PEX be isolated from the foam? I thought about the foil covered paper used over basement insulation or 15# felt stapled below the heat.
Thanks in advance for whatever advice or comments you can give.

Jeff Lawrence_25

Let's see....

Staple up can possibly cause striping. Striping is where (to me) one section of the floor right over the tubing will be warm and the rest will be cooler, especially if they foam it.

Plates will reduce the water temps necessary from as high as 140 degrees to something closer to 100 degrees, saving $$$ because the heat source won't have to expend the energy to heat the water the extra so many degrees.

You can use a product called Thermo-Pan between the tubing and the foam. Even if you use plates, it's recommended that you install some kind of a break between the spray foam and the plates because the foam does have a tendency to get between the plates and the subfloor, insulating the heat transfer slightly and in a few places where the plates don't actually come in full contact with the subfloor.

These are a couple of things right off my head. I'm sure several others will chime in.

Unknown

What is the heat load of the space, in BTUs per square foot?

That is what determines whether you need plates, really want plates, or not.

If that has not been calculated, it should be.

Edit: also, what is the heat source here?

bruce_21

The load in btu/sf is 25.5 or 18 depending on which wholesaler's calculation I believe. My I=B=R calculation worked out ot 27 btu/sf but I'm not sure about the infiltration factor to use especially with the spray foam which I hear reduces the infiltration a good bit. The total load is about 20-25K btu. This is new construction with good windows so it should be quite tight. The heat source is undecided, I'm leaning to a LP fired water heater with a coil in it like the Lochinvar or Appollo or a reg Lp water heater with a flat plate exchanger depending on the overall cost.

Unknown

If those numbers are accurate, you want plates.

Tell the flooring installer to use short nails.