Radiant wall heat behind corrugated steel
Has anyone done in wall radiant heat behind corrugated metal wainscot?
1st floor is concrete and will have in floor heat. Looking to possibly heat second floor with in wall heat, pex placed between sheet rock seams horizontally 12” oc possibly with heat transfer plates, and then galvanized corrugated steel placed over the assembly as wainscot. Would running a bead of silicone over pex before applying corrugated provide good heat transfer? I think this is a good idea in that the corrugated will provide good heat dissipation and also protect the pex from being punctured with screws. Walls will be r30 and thermally broken.
This is a my preliminary thought and without getting too far into design calculations, and such, I’m hoping to pick your brain as to whether this is a viable option. Climate zone 6. Thanks!
Good or bad idea?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I don't like it. Galvanized steel has a pretty low emissivity, around 1/4 to 1/3rd of non-shiny metal surfaces (ie typical radiant floor/wall surfaces), which will severely cut down its output. And I don't think you'll get good conduction contact between the PEX and the metal, being corrugated (silicone or not). Look at the design of a radiant ceiling panel - large, flat, non-shiny surface with large metal spreaders behind that the tubing clips into (or is pre-soldered copper piping w/ fins). Unless you can achieve something similar - and maybe paint the steel so it's got a higher emissivity) - I wouldn't expect this setup to work that well. Maybe in a milder climate zone, but not 6.
Yes, silicone will improve thermal transfer. I’ve actually done this before (use silicone like this), but in a completely different application. While silicone caulk isn’t a great conductor of heat, it is MUCH better than air. The difficult part will be getting a consistent bond without air gaps as you assemble the wall.
Painting the galvanized steel flat black will help with emissivity, black is best but anything helps over shiny steel. It will work as raw galvanized steel too. This is just like heatsinks for thermal dissipation, flat black is best, but anything — including shiny raw aluminum — works too, just not quite as well. Keep in mind that plain old fin tube in radiators usually has a shiny copper pipe with shiny aluminum fins and it works just fine.
I think your most difficult issue is going to be getting the PEX in good contact with the galvanized steel; and keeping it there as you put the wall together. Any separation will hurt performance.
Bill
Thanks Bill. My other idea was putting 1 inch foil faced polyiso inside of my 1.5 inch service cavity (air and vapor barrier behind that along with r23 stud cavity) and then stapling tubing without heating fins to polyiso and then Sheetrock over that. What do you think would radiate the heat the best if tubing setups were identical?