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Old 12-27-2010, 02:15 PM   #1
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Radiant Floor Heat question - suspended slab


We added radiant floor heat to our office floor, which is a suspended concrete slab over the basement. The slab is about 5.5" thick. We Ramset'ed 2x2 furring strips to the concrete on 16" centers, ran 1/2" PEX tube between the 2x2s (2 tubes per "bay"), filled with sand, and covered with plywood.

The office is about 650 s.f. We have a 105 net BTU boiler, a newer Burnham PVG. We ran 4 loops, each loop being no more than 300'.

We've run the boiler for about a week now, and the office has never gotten above about 63-64 degrees. We started running the boiler at 140 degrees, and we have steadily increased the temp to 180 to see if the office would warm up. The boiler takes about 2 minutes to warm the water up to the 180 degrees, turns the burner off, cools to the low temp setting after about 2.5 minutes, and kicks the burner back on.

We have a heat sensing gun used to test steam traps, and the floor is running in about the mid 60s. The ceiling of the basement is running in the mid 90s.

We glued 2 panels of insulation to the ceiling and that lowered the temp of the basement ceiling to the mid 60s and increased the office floor temp 5 degrees.

Any suggestions as to what's gone wrong? The office won't get above the low to mid 60s.

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Old 12-27-2010, 06:07 PM   #2
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Radiant Floor Heat question - suspended slab


Quote:
We Ramset'ed 2x2 furring strips to the concrete on 16" centers, ran 1/2" PEX tube between the 2x2s (2 tubes per "bay"), filled with sand, and covered with plywood.
Ayuh,... I just finished building my 1st radiant system last fall,...

My uneducated Guess is,...
You shoulda rolled out reflextex type insulation on the concrete, Before you did the wood, tubing, 'n sand...
I Think it would force the heat Up, rather than Into the slab....

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Old 12-27-2010, 08:43 PM   #3
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Radiant Floor Heat question - suspended slab


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Originally Posted by Bondo View Post
Ayuh,... I just finished building my 1st radiant system last fall,...

My uneducated Guess is,...
You shoulda rolled out reflextex type insulation on the concrete, Before you did the wood, tubing, 'n sand...
I Think it would force the heat Up, rather than Into the slab....

That would have helped a lot.

Also, should have used 6" OC,
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Old 12-27-2010, 09:18 PM   #4
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Radiant Floor Heat question - suspended slab


I don't believe that sand & wood are very good heat conductors. They are much better insulators. Why did you cover the slab with plywood?
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