Floor Output

Alan (California Radiant) Forbes

I have a customer that routed 3/8" PEX in a plywood floor.  He is covering it with 1/2" plywood and then 5/16" cork.  Can anyone tell me the BTU output per square foot of such a floor?



Thanks.

Charlie from wmass

more questions first

water temp, loop lengths, pump used for an idea of the gpm. any heat transfer used like caulking and/or aluminum plates?

Alan (California Radiant) Forbes

No Plates

Yes, unfortunately - so far - no plates, so output will be limited.  Water temperature - 130 degrees and no caulking.

CMadatMe

R-Value

The ply is easy that has an R-value of .63. The 5/16 cork is what? Tile or flooring.



Try this......   http://www.wecork.com/products/floor-tiles/installation/

Alan (California Radiant) Forbes

Let's try again

The plywood is actually 5/16" and the cork is 1/8".



I'm helping a friend out with his garage/work studio addition, but he got a little too ahead of himself and routed the bare tubing into the floor.  I'm afraid his output will be less than 10 BTU's/sq. ft. and he needs 40 BTU's/sq.ft.



I suggested Raupanel and Thermalboard, but he thinks it will be too much work or it's going to mess up his floor elevations.  I've suggested a large Runtal radiator.  The heat source is his domestic water heater via a Taco X-Pump Block.  Any other ideas?



Alan

NRT_Rob

that will be better

than naked staple up pipe. I think you'll be around 15 BTUs/sq ft as long as you're around 8" o.c. with 130 degree SWT and a reasonable drop.



you were never going to get 40 BTUs/sq ft out of a radiant floor anyway though, unless you were doing concrete and tile or something.



I'd recommend radiant ceiling and a 120 SWT max. If you really need 40 BTUs/sq ft you'd want 8" o.c. or so.

Alan (California Radiant) Forbes

Excellent idea, Rob!

It would have to go in the wall since it's an exposed beam ceiling.  What product do you prefer?  Raupanel? Thermalboard? QuikTrak?

CMadatMe

Have You Thought

About adding a panel rad sized for the same temp for make up or even radiant panel baseboard as an additional loop? Take the kick molding off the wall and replace it with panel board. Same look better feel.

hot_rod

also check out

some of the low temperature radiators from Jaga..They give amazing output with 90- 100F supply.  Some really wild styles too.



Smith of MA has a large fin, low temperature baseboard.



For a retrofit wall check out the Roth panels.  Foam with aluminum surface.  use foam adhesive to install them then a covering of sheetrock ot thin, engineered wood products.



The floor output is related to how warm you can get the surface temperature without damaging any of the coverings.  The rule of thumb is about 2 btu/square foot for every degree difference.  80F surface- 68 ambient = 12X2 about 24 btu/ square foot.



hr

NRT_Rob

usually

we just use light plates and PAP tubing with 1x3 strapping. if I was going to do a prefab I'd probably opt for warmboard.. would be more stable for drywall... but Roth would be good too from a thermal standpoint, I just don't know about drywall over roth... maybe you would need sleepers?



Wall is great for a couple of reasons though, first you still are only fighting drywall for heat transfer, and second people will tolerate huge temperature asymmetries in walls. so if you had a tile section of wall, for example, you could really crank out the output with higher water temps (drywall wants a 120 max I've been told). but I get concerned about puncture risk and typically prefer radiators for the visible obviousness/lack of puncture issues.

Alan (California Radiant) Forbes

Gypsum and 120 degrees

So, using a product like Raupanel on the wall, why does the gypsum limit water temperature to 120 degrees?  Does it break down? 

Mark Eatherton

Gyps not the issue....

Paint and wall paper glue are the weak components in the mix. I think that Siggy first recommended those limits when he did his wall. I've run 160 degree F water through my gyp/paint radiant ceiling in an effort to accelerate a cold cabin, and I forgot to turn it down, and haven't suffered any paint peeling off the ceiling. Of course, I am running on an outdoor reset as well, so it only sees real hot water 2% of the time.



ME

Alan (California Radiant) Forbes

Thanks, Mark.

I wonder how water temperature relates to surface temperature, i.e at what wall temperature does the paint start to peel?

NRT_Rob

we question it

it is supposed to hurt gyp to get too hot, but we had a client doing VSI on a cast iron boiler that had serious heat migration/ghost flow through the injection circuit, turning his radiant ceiling into an on/off high temp emitter. and no issues noticed over a couple years of operation. but I abide by the 120 because it does give a max output that is in like with the max limit for thermal comfort, I believe.

hot_rod

possible expansion issues

when a sheet of sheetrock goes from room temperature to 120F or more?



hr

Mark Eatherton

No sheetrock issues on my watch...

In fact, my unheated ceiling has more cracks than my heat ceiling does.



I do agree that having real hot water going through the panel does make for hot head syndrome tho...



ME