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Old 08-15-16, 11:15 PM   #6
Steve Hull
Join Date: Dec 2012
Location: hilly, tree covered Arcadia, OK USA
Posts: 829
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JR - I already have a geothermal heat pump and I am talking about building with SIPS. I have done other homes/building with SIPS and am comfortable with them. Am recycling the thermal double pane Pella windows as well as air to air heat exchanger, etc.

The specific issue for radiant flooring is the cost vs. benefit for my location in Oklahoma considering the relatively short winter.

I grew up in New England, did grad school/post docs at Michigan State so I certainly know about really cold winters (as you do).

Will do the radiant myself, so labor is not the cost issue.

One major issue is overheating as thermal floors have a long lag time and we often have winter bursts that are frigid, but a few days later, the temps are in the 40s. A recipe for overheating.

I have done the manual J modelling with a 60% contribution from the geo air unit and 40% from radiant. The flooring is not a hot floor - but a conditioned floor, about 72 or so F. Set air temp at a couple degrees lower.

For that reason, the floor concrete surrounding the PEX tubing will not be 4 inches thick, but perhaps only two inches.

I will likely use a water to water geothermal heat pump to provide hot water for the floors and I already have a drain back hot water solar system. Then I also have the desuperheater from the water to air geo unit. I have LOTS of hot water in the summer.

Anyone down south use radiant flooring? Or maybe I should just go with electric radiant - even thought I hate the idea of using 60 Hz electrons for resistance heating . . . .

Electric radiant is cheap to install, but pricey to run.

You don't need to ask why we need a ducted air system - been close to 100 F for the last couple of weeks. Forced air A/C is not a luxury down here - it is a necessity.

But we have a LOT more cold weather also - temps down to zero F. That is a lot of heating degree days (60-70 each days when it is that cold), compared to the need for a daily cooling degree day on a hot day of about 1/2 that. So we have a dominant heating need.

consulting on geothermal heating/cooling & rational energy use since 1990
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