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Radiant under wood floors
I'm restoring an old house and thinking of putting radiant heat under the wood floors because all the joists are accessible. Does anyone have experience with how the PEX shoud be attached and if insulation should be installed under the PEX. If so what type of insulation?
Thank You
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First you want to make sure tar paper or horse hair is not used between the floor and sub floor or any material to give off an smell when heated ..
Your also heating Wood , and extra care is needed to protect it ..
You don't want to constantly heat and cool the wood .. Outdoor resets and floor sensors will help maintain an near constant water temperature supplying the floor .
Humidity control is also an must , since the wood is an sponge you need to maintain moisture in the wood . Me I like an good steam humidifier and an humidistat with and outdoor sensor .. You will need to drop the percentage of humidity when the outside temperature drops below freezing as to not condense in the walls..
Me, I am not an fan of wood radiant , I love radiant in Kitchens and baths . Kitchens with its lack of wall space.. Baths for it lack of wall and construction materials ..
Plates. You want to attach the pex to the underside of the floor using the heaviest plates you can find. I used Thermofin plates from Radiant Engineering. While not inexpensive, they make installation a breeze, and ensure no noise while operating. Do not use the thin, tinny aluminum sheets, you will have poor heat transfer and obnoxious noises from the pex moving around. Also, conduction is key. The underside of the floor must be flat. You need to have a good area of contact with the plates.
Insulation. I put R19 fiberglass batt insulation, tight to the underside of the tubing/plates. No air gap. Make sure you joist sills are tightly sealed and insulated. You want the heat to conduct up, not down or out the sides. I installed a Tyvek type of barrier under the insulation to keep the insulation from dropping (and because it is a friable material, which I don't want to be breathing in/contaminating my basement).
Thickness. My system is a combination of wood floors and limited carpet. Most of it is 3/4" plywood + 3/4" white oak. The thicker the floor, the harder it is to drive the btu's through the floor.
Make sure you perform an accurate heat loss analysis before committing yourself to this endeavor. Most systems won't do well to go above 30 btu per square foot. There are other radiant options as well--ceiling and wall.
A word of caution. This is not a project to jump into without good planning and sound design. And, you may become addicted to hydronics. I'm a pharmacist by trade, but read this website every day. (Hardly ever comment though, everyone else on here is far more knowledgeable.)
Roy
Making sure you have a system that monitors and controls the temperature to the floor and that it doesn't go too high is essential. Our plumber didn't install floor sensors and we have areas where the floors start to pop.
The insulation should go up tight to the bottom of the subfloor and the rim joists should be insulated and sealed with spray foam. Some people cut blocks of rigid foam to insert in the rim joists cavity and then use spray foam around the edges to seal it.
I would stay away from a suspended tube system.
Reflective foil backed insulation is a waste of money.
Design the system to run on the lowest possible water temp and control the water temp via outdoor or indoor reset control.
Design the system to run about a 10 degree DT.
Go for it!!! Done right, you'll love it!
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Rooms with a lot of furniture, throw rugs, or high loads need to be calculated carefully.
It is also quite possible that a system like UltraFin is adequate in low load rooms or areas. Without a load calc it i all just guesstimates.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me