Considering this radiant setup


Old 01-18-16, 05:39 PM
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Join Date: Jan 2011
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Considering this radiant setup

I recently replaced the 1st floor floors in my 3 story Philadelphia row home. I removed my cheap baseboard heaters on floor 1 intending on using cast iron radiators I have in storage to replace them. I am currently using a mini split heat pump to heat the first floor which works well down to the mid 20s out door temp then the room is not as comfortable.

The boiler is in the basement and I have access to the floor joists from there. 3 zones, one per floor. 3 valves, one pump
The boiler is a 140000btu unit with the temp set to 180
floor is 3/4 pine tongue and groove with pergo over it. There is sound deadening foam under the pergo.

I have 275 feet of joist bay. Bays are spaced 18-20"

I would like to use radiant to heat this zone. I know its advised to have lower temps than 180 but I do not want to install a mixing valve and separate pump for this zone.

I was thinking 2 275ft circuits of 1/2 pex. Or maybe 3/4? Can I get away without the heat diffusers? Any cheaper alternative. Flashing stapled up to floor?

The baseboard that was in the room was 12000btu and while it heated the room, it was slow to warm the room up. The room is 424sqft
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Old 01-20-16, 03:53 PM
Join Date: Jul 2009
Location: Toronto
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NEVER staple pex to the underside of the subfloor.
PEX has a pretty good amount of thermal expansion and it will create a ticking noise at every staple.
We use a ton of Watts Radiant Onyx tubing for staple ups. there is very little thermal expansion and no noise issues>
While you could put 180 thru the tubing, I don't think I would. Thats pretty hot against wood, and there might be some fear of drying it out and combustion (thought I don't think it's hot enough to actually cause combustion).
Mixing valves are pretty easy to install

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