I'm building a new house in central Pa with an insulated slab on grade. I need lots of thermal mass to even out gains and losses through a Frank-Lloyd-Wrightish bank of south facing windows. (Yes, I know.) It's a no-brainer to tie pex to the rebar, but I can't get an answer to this question: Has anyone married a European-style stove/boiler to radiant? www.hydro-to-heat-convertor.com/ or www.esse.com/stoves/multifuel_wood/700.html I know that mixing valves can deliver water at the right temperature, but how much heat can you actually transfer to the slab if the stove is putting out 27k btu (Esse) up to 100k plus (DDG)? If transfer rates are significant, how would the slab perform if I turned up the thermostat and poured it on? The idea would be to substitute determined but sporatic wood burning for fossil fuels, even if it meant skivvies one day and long johns the next. Has anyone tried this?

Toddm,

I have not tried nor heard of what you are suggesting, but two possible problems come to mind:

1. What max temps would the stoves be putting out, and how does that relate to the max operating temps of the PEX tubing?

2. If you are talking about very large delta T in the slab, it could induce a lot of expand/contract breakage of the concrete. For example, are you talking about going from 50F to 100F regularly?

I have no idea if these are legit. concerns, they are just what popped into my head when I read your post.

Another idea to consider is to create a larger thermal mass, in the middle of your slab by NOT insulating under that portion of the slab and running your pex deeper into this mass(pea gravel/crusher fines/other material) so that you can sttore more heat not at a higher TEMP, but by using a larger storage mass.

Dave

I should have plenty of mass in a 1650 SF frost protected shallow foundation, which will be upwards of 50 tons of concrete counting the footings and beams. I wonder if you could raise its temperature by even 10 degrees over two or three days of wood burning. Cold snap over, it might take another two or three days for the excess heat to dissipate. That's what makes this an intriguing prospect -- the ability to bank heat using radiant's normal parts. But I don't know enough about those parts. If you sized the system to handle the stove, how would it work under the normal, admittedly opposite, parameters of small additions of heat in a stable system? A small stove would narrow the difference. Even if the banked heat only carries the house overnight, I've substituted abundant wood for expensive heating oil at the right moment. Any wood burners out there?