Radiant Floor Heat

[Jim Andrew]

Treated poles just do not have as long a life as creosoted poles. I see Morton buildings replacing the rotted bottoms of poles on neighbor's buildings. What they do is dig out the pole and sackcrete, pour the existing hole full of concrete and use flat steel on both sides of the pole with bolts through it to anchor it. Seems to me that would be the right way to build a pole building in the first place, rather than to bury the wood in the ground. Morton does have that option now.

[Scott T Smith]

My 1/2" tubing was installed in 300' max runs, but the distance between the tubes varies. The first couple of slab perimeter runs were on 9" centers, then 12", then 18', and then 24". The bulk of the slab is 24" centers and I have no problems with hot spots. My slab is 6" thick and there is 3-1/2" - 4" of space between the top of the pex and the top of the slab. The reason for the closer perimeter spacing is because this is where a lot of heat loss occurs.

I would do two things different. First, I would figure out a way to insulate the perimeter of the slab. Because two sides of my slab are on top of a concrete retaining wall, this would require some thought. Second, where all of the pex comes together to exit the slab, I would insulate some tubes as this portion of the slab is warmer than the rest due to close tube proximity.

[Matt Hagans]

Does anyone have experience with Radiant Heat in concrete UNDER 2x4 sleepers and CDX ply over the concrete?

[Mark Kornell]

I've had experience with radiant heat under Dricore + 3/4" ply. The radiant heating still worked, bit the extra layers and air gap acted to add a bit of thermal mass and insulation between the PEX tubes and my feet. The net effect was that the subfloored space ended up about 2°C cooler than the adjacent non-subfloored space and it also took longer for heat changes to be felt. Despite that, it was well worth it in terms of being easier on the feet and knees.

I would expect a 2x4 + plywood subfloor would have a similar but smaller effect.

[Mike Heidrick]

I came across 40 sheets of 1.5in r7.5 Sat for $5 a sheet so I bought it. 40+ more sheets to go. Not 2in but at $200 vs $1000 I vent with it.

[Deb Clarkson]

My workshop is in 1/2 our basement. We put RFH in the slab over 2" of foam. I love it! Since it's part of the house I can't tell what the heating costs for that space are, but I can tell you how comfortable it is. No dust from a forced air system being blown around and into the rest of the house. I am perfectly comfortable with the tstat set at 68. When we lived in a house with a heat pump I set it at 76 and still never really felt warm enough. The only possible downside to RFH in a slab is there's not much point in setting back the thermostat at night because the slab will have barely stated to cool by morning. It also takes a long time for the air temperature to come back up once the slab has cooled, but it doesn't really matter cuz once that floor's just a little warm you're comfy even if the air temp is only 50.

[Scott T Smith]

Also would you run 1/2" pex and shorter 300' max 12" on center loops or 5/8" and 500' max 16" on center loops. Price is similar.

Mike, I would think that the larger sized pex would not be as desirable, because of the larger surface area as well as the longer run. By the time that the heating fluid made it through that long run it would have cooled off significantly. The 1/2" / 300' run is sized to allow for the proper amount of heat transfer.

[Mike Heidrick]

Scott, I went with 2700ft of 1/2 inch. Did the pole barn kit from blue ridge with a 9 port manifold. Have 3 huge boxes of pex now - time to make an uncoiler.

Also found another 150 sheets of 1/2 inch polystyrene so that will make for 50 sheets of 1.5 inch.

What boiler btus size did you go with? Or what size water heater?