pavilion radiant heat

utahDIY

Hello everyone,

I am planning a 12' x 16' pavilion in my backyard and looking into the feasibility and wisdom (or lack thereof) of putting in a radiant heat slab under it. I would enclose the sides with canvas or something of that nature in the winter time. I want the radiant heat to be powered via wood fire (wood stove, etc.). Could anyone tell me if this is possible to build? Also, would anyone know if radiant heat would be enough to heat this space to 60 + degrees F?

DCContrarian

I don't think it would work well for this application. You want something that can deliver a lot of heat in a short period of time, that's not really the forte of heated slabs.

The heat output of a floor is entirely determined by its surface temperature. In order to output enough heat to warm an uninsulated outdoor space you might find that the floor is too hot to walk on.

EdTheHeaterMan

Probably not enough to heat to 60° based on a load calculation where the side walls are canvas only. I helped a Wallie last year to get the proper radiator size to heat a glass room that was attached to her home. The room was all glass. It seemed that the plumber that installed the boiler figured that the room just needed a 12 ft section of baseboard radiator to heat a 13 x 25 ft glass room. It turned out that the radiator for the "Solarium" actually caused the ModCon boiler to fail because the return water was too hot. This was discovered after a factory tech support visited the house and found that the 3/4" loop was so short that the water was returning to the boiler return inlet too quickly and offering very little heat to the room.  Not enough temperature drop when only that zone operated.  Which was all the time.

I did the load calculation based on Hydronics Institute Form 1540WH.  I set up the walls as 9’ ’1” x 25’1” then used a window that was 9’ x 25’  the same thing for the two sidewalls that were 9’ x 13’ , and the ceiling was 13 x 25 glass. This made the load calculation of over 35,000 BTU, and that needed more than a 12’ section of baseboard.

You need to do the same thing.  Do a load calculation based on the construction of the roof and insert walls that have no insulation, and no thickness.  No siding, no sheetrock, no nothin.  And the infiltration will be above the charts.  Like maybe 10 or more air changes per hour.

With that load calculation you will find that the water temperature in the slab may need to make the floor 140°F to get the room to stay at 60° room temperature.  I believe that might be too hot to walk on.  

I have actually had experience with this. I built an awning to cover the HotTub on our back paver patio. We had vinyl/canvas side curtains made that rolled up in the summer and were deployed in the winter.  When we decided to use the HotTub on very cold days, that HotTub surface area of about 38 sq.ft. at 110°F warmed up the room by about 15° above the outdoor temperature.   Not very warm for a 17° day.  We also added an electric space heater on the other side of the enclosure (you don't want an electric space heater sitting on the edge of your hot tub) And that made the room go above freezing, but no way warm enough to sit outside and read a book.  

I believe that gas fired infrared heaters hanging from the ceiling may be your better option.