Mixing valves/radiant infloor/woodboiler

Old 09-12-05, 05:40 AM
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Mixing valves/radiant infloor/woodboiler

I have a wood boiler ( on older "The Furnace Works" ) tied in with a 25 kw Chormalux electric boiler. I am adding an addition where I want to install slab infloor radiant heat. I also want to add another loop via infloor under wood with the heat reflectors etc.
I talked to one contractor that expressed concern about the infloor in the slab. He was concerned that because of the fairly big swings in temperature in my system that the PEX may crack my floor.
I understand that you need a mixing valve to keep the Pex under 140 deg. How reliable are the mixing valves? how could you tell if they have failed. What would be the result to the PEX in the floor in the event of a failure?

This is a fairly experienced plumber heating guy but I have built/designed a couple of slab on grade houses with oil boilers and know they work.

Any thoughts?
Old 09-12-05, 06:43 PM
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In slab PEX

I'm no radiant guru, but as I recall, you don't want to even think about approaching 140. It seems to me, you want to stay around 110. Tempering/mixing valves work well.
Regarding the potential damage to the PEX: I don't thing the tubing would be in as much danger as the slab. Be sure to use a tubing with an oxygen barrier.

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