Radiant floor heating house plan

[TheRooster]

Hello All,

I have a 1200 sq.ft house with a crawl space. I would prefer to have radiant floor heating as a primary source of heat. Installing it on top of the existing subfloor is not an option. I was hoping to drill holes in the crawl space and run my loops as close as possible to the subfloor.
All my joists are 16" O.C. The house is a rectangle. 50'x 25'.
How much spacing would you put between each 1/2" pipe? Any other recommendations would be greatly appreciated. Looking forward to your input!

 

[LopezBart]

You would likely need:

• A lot of insulation between the joists so you don't heat your crawlspace.
• A high circulating water temperature because of the high thermal resistance between the pipe and the flooring.

You will want to talk to an engineer who designs hydronic heating for a living on this; my gut tells me this is going to be pretty inefficient. If you can calculate the R value of your existing subfloor + finish flooring, you can estimate what the temperature of the PEX would need to be to move enough BTUs through the floor.

 

[TurnipTruck]

You definitely want some staple-up heat transfer plates. IIRC, a bare pex tube in a joist bay is 7 btu/ft while the double tube plates are 28 btu/ft. The difference is incredibly apparent to a thermal camera through the floor.
,,

 

[chinboys]

I have a split level ranch with a 30x30 square feet living room dinning room that I used heavy duty aluminum 1/2 inch dia Pex track heat transfer plates that I screwed into the bottom of the 3/4 inch planed diagonally subfloor. Two plates per bay along the length of each bay and each bay is 16 Inches on center for the floor joists. There is 3/4 inch oak tongue and groove floor on top. 300 foot loops using oxygen barrier Pex. Yes, I drilled 1 inch holes at each end of the 2x 8 floor joists and wove the loops of Pex on my back and side as my crawlspace is 4 feet in height.
Two circuits are feed off my 6 port manifold by two thermostats (Nest and Ecobee) with a Pex temperature water mixing active mixer (can't or shouldn't send water hotter than 105 degree F to heat wooden Floors when my boiler is making 125-180 degree water for my other zones that have radiators on them).
The mass of the floor makes a great heat sink radiator once the heat transfer via conduction happens. The bays are also insulated from the cold crawlspace.
I keep the room temperature set at 68 degrees and the floor feels warm.

The water temp leaves the manifold at 105 and returns back at 90 or higher if I increase the active mixing unit's flow per minute (it is set for low right now).

 

[MongoTA]

Hello All,

I have a 1200 sq.ft house with a crawl space. I would prefer to have radiant floor heating as a primary source of heat. Installing it on top of the existing subfloor is not an option. I was hoping to drill holes in the crawl space and run my loops as close as possible to the subfloor.
All my joists are 16" O.C. The house is a rectangle. 50'x 25'.
How much spacing would you put between each 1/2" pipe? Any other recommendations would be greatly appreciated. Looking forward to your input!

No idea what your climate is, but generally two runs of pex per joist bay.

I did staple-up. Added 1/2" foil faced polyiso rigid foam board under the pex, friction fit between the joists. Added R-19 FG batts under that.

Make sure you insulate the foundation rim board. I did two 2" thick pieces of XPS, friction fit, total of 4". Also cut on the table saw then friction fit in place. Alternative is to cut them maybe 1/4" too small and use canned foam to seal the gap.

 

[LopezBart]

Our house also has hydronic heating... We wanted a low maintenance floor so we went with 4" regular tinted concrete over a very sturdy floor system. We have a heat pump that warms the water, and also provides domestic hot water preheat; not having to heat the water really hot to transfer heat helps the heat pump be more efficient. Floor temperatures are actually pretty low most of the time, not much above the 67F at which the thermostat is set.