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I’m building a house in upstate NY (living in the basement right now) and have framed it to be heated by a Russian fireplace (not built yet, which is part of the reason we’re living in the basement). I’m thinking about installing some radiant (floor) heat to supplement in some rooms (bathroom, study, 1 bedroom)that will be furthest from the fireplace. Went back and looked at a discussion that took place in early Feb and got some useful info but I have some other questions: Everyone emphasizes that part of RFH’s advantage comes from heating thermal mass – will I get acceptable results from just installing beneath subfloor (already down)and hardwood flooring(not down yet)? I have a 50 gallon electric water heater I’m using now but have an on-demand propane water heater I want to hook up once we’re fully moved in. Could I use the electric water heater as my source for the radiant heat? One drawback to that, of course, is that electricity is most likely to fail just when I’ll need the heat most, in severe winter weather. Can I do any kind of tie-in with the Russian fireplace to heat my radiant-heat water? I’m sure I could think of plenty more questions but that’ll do for starters. Thanks in advance. John
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John,
You're describing "staple-up" installation. The PEX is stapled to the bottom of the subfloor. You then need a radiant barrier and some R-value inder the tubing to help direct the heat where you want it...up, through the subfloor, and into your living space.
Typically, under the tubing, half-inch foil-faced polyiso RFBI is cut and then friction-fit between the floor joists. The RFBI can be tucked up against the staples. Under the RFBI, usually additional FG batt insulation is installed. Use unfaced batts, and if the basement is to be unheated, you can use R-19.
Staple-up installations usually require water to be circulated at a temp of 105-140 degrees...it depends on your requirements. A water heater can be used to carry that heating load. You could have a backup source of electricity to power the electric WH when the grid goes down.
I'm not knowledgeable enough to give you info on how to tie a heat exchanger in to your russian fireplace. I've never done it, so I don't have much to offer there. I do know that people have installed a serpentine of tubing encased in the mortar fireplace...as well as more conventional heat exchangers...I just can't offer specifics on how it was done.
While thermal mass can certainly hold heat and it dampens temperature fluctuations, it isn't a requirement of radiant floors. IMO the biggest advantage of a radiant floor is the warm floor ... about the only part of a building that touches your body consistently.
I disagree w/ the other poster ... he says you describe staple up, but you can put it on top of the floor. Personally, I like it as the subfloor/sheathing separates it naturally from the space below. You can use the premade tracks to snap the tubing into. I made my own w/out much trouble. Cut 3/4 plywood into e.g. 8 inch strips at a 10 deg bevel. I had a stock curve template for the ends. I laid tubing and screwed the plywood down at the same time. It worked great. This adds 3/4" to your finished floor. If you are a DIY, I think this is an inexpensive and easy to do approach that is more effective than staple up from below.