I would like to hear opinions on if I can get benefits of thermal mass by stacking bricks or if it's better to use firebricks around my woodstove? -Thanks, I'm sure there are people more knowledgeable than on this subject. We live in Saskatchewan,Canada and we get winters with at least 2-3 weeks of -40 if not real degrees, the wind chill factor and the rest of the winter is -25 to -30 Celsius.
I'm actually thinking about doing something similar with my woodstove. One thing I would make sure of is to get some dense bricks. We'd picked up some bricks off craigslist a few years back, in hopes of adding mass to our stove. But, the bricks are really light and porous. They barely get warm, and don't stay warm for very long. I'd love to get some soapstone bricks, as those heat up welll, and stay for a loooong time, but they do look terribly expensive...
I don't think there is any significant difference in thermal mass and storage in a refractory brick versus a regular fired red brick, or even concrete. I expect the difference would be <5% between them. The biggest difference is the refractory brick will survive to 2000F or so, and it's ugly. Lots of mass does wonders in the woodstove surround. If you want to spice it up a bit, you could put some phase change material behind the thermal mass. Phase change material works like a thermal battery, storing energy until it's chemical threshold is reached, then it dumps out the energy very fast. You can make your own if you were a quick study in Chemistry in HS or college. Many put it in PVC pipes, but it's also sold commercially in bubble wrap sheets for green buildings behind drywall. It's very compact for it's energy storage capabilities.
As someone mentioned above, Soapstone has the largest thermal mass capability, but it's expensive.