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# Staple up radiant under thin concrete?

Member Posts: 10
Hello I've learned a lot from this forum. I have a question. My living room floor is a little unusual. It consists of a ~3 inch thick concrete slab supported by wood floor joists. The room is over the garage. The slab is reinforced with 6x6 WWF so it has a structural component. There are sawn lumber boards (3/4 inch thick) between the joist to form the original slab. I would like to install a PEX staple up with metal heat transfer plates attached to the sawn lumber between the joists and I wonder how well the heat will transfer into the slab above. Has anyone seen this configuration? Of course I would insulate the joist bays after the install. One of my concerns is I don't think the concrete is in intimate contact with the lumber anymore as the wood has shrunk and cracked and warped over the years. Thanks in advance for any input.

## Comments

• Member Posts: 7,569
What is the heat loss of the space?. I have done this before with marginal success. You can get the heat through, the lag time is a bit of an issue.
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Member Posts: 10
Heat loss is something like 54000 btus and the slab is 21 x 19 ft if memory serves, guess I should calc the max typical BTUs for 400 sqft slab emitter. The room has alot of windows
• Member Posts: 10
heatloss is closer to 35000 btu/hr
• Member Posts: 7,569
Double check the heat loss numbers. Assuming the room is enclosed, those numbers are way high.
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Member Posts: 22,118
What about floor coverings? Add up all the build up and develop an R-value.

An accurate load calc will indicate heat required, convert to btu/ sq ft, then see if the radiant could cover the load.

If the wood is warped and not in contact, that would be a deal breaker.

Radiant ceilings, walls or panel radiators are other options.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 10
Thanks for the comments! I think I will "scrub" the infloor idea and go with panel radiators, will look at ceiling as well.
• Member Posts: 22,118
Radiant ceilings get you about 60% more heat output compared to floors due to higher surface temperatures available.

90+ % is delivered by thermal radiation, it warms anything within "sight". Floor radiant is some conduction and some convection heat transfer.

low mass quick recovery, and shutdown. Sometimes easier to retrofit.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 10
What are options for hydronic radiant ceiling panels? Warmboard? anything "home grown"?
• Member Posts: 22,118
Plenty of options. There are "dry" assembly panels available;e, Roth Rehau, Uponor, Watts, Viega and many other aftermarket brands.

Or just buy the extruded aluminum transfer plates and customize you own design.

I imagine there are a lot of variations on installation details.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 10
What about used solar thermal panels from craigslist? That's a joke, sort of... it would probably work
• Member Posts: 22,118
nothing conducts and moves heat like copper, well maybe gold

Sure, if you can get adequate square footage. If they are ladder style absorbers reverse return pipe them for counterflow circulation.

If they are small tube serpentine, be awarenesses of pressure drop when you combine them.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 10
probably should take off the glass and make sure they are mounted upside down or just take the plates and tubes out of the housing
• Member Posts: 22,118
This wall radiator is built out of an old Revere thermal collector. It warms in seconds when flow hits it.

1977 version absorber, back when the copper was still about 1/16" thick. Modern absorbers are paper thin copper.

AET solar in Florida will sell you copper fin strips, if you really want a copper system
http://www.aetsolar.com/thermafin.php
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream