Thanks for the reality check on the radiant heat output HM, that will give me a bit better idea... The other option of course is that since the living room (which is the only "problem" room for heating, BTU requirement wise) has the woodstove in it already, and that won't be taken out, is to go for the 25-30 BTU/ hr / sq ft range, and figure on using the woodstove on those days when the radiant isn't quite enough...
The basement construction discussion is also interesting - the basement in our circa 1980 built house is poured concrete, presumably w/ rebar, I think 10-12" thick. It sticks up about 4' above grade, and 4' below grade, with the local water table not much below that during at least some parts of the year. Currently most of it is finished w/ 2x4 studs, fiberglass bats and individual board panelling. The floor is a concrete slab w/ carpetting glued down on top of it. I like the look of the board paneling, but the insulation doesn't seem to do much, as the basement stays cool to cold year round, and by the Slantfin heat loss program seems to be the biggest single heat loss in the house... When the GF bought the house she had a radon test done, and got mixed results - essentially they said it was probably higher than would be OK for someone living in the basement, but not a problem for using the space otherwise. We have a sump pit, and the pump runs heavily during the spring thaw season, and sometimes after extended rains, otherwise not. No direct signs of moisture otherwise, but the dehumidifier we keep down there runs quite a bit.
I would like to pull down and salvage the panelling, redo the walls and floor w/ better insulation, and put the panelling back up. Presumably it would be nice to also do something that would reduce the radon, and avoid any moisture related issues.
From what I've seen mentioned, it sounds like frost in the basement walls is not a big concern? I haven't seen any real concensus on how best to approach redoing the basement insulation. Digging down to insulate the exterior seems problematic, as does covering the outside completely due to the potential insect problems.
As best I can get from the Building Science website, the best approach to dealing with insulating on the interior is to cover up to about grade level with a vapor permeable foam, and above grade level with a vapor proof foam so that the concrete could dry to the inside below grade, and to the outside above it. The floor they said should be covered w/ a layer of "Enkadrain" (presumably tieing into the sump pit in some way) and then a vapor barrier and floor system - I'm thinking of one of the "foam mushroom" type panels (Creteheat or one of the similar items) with radiant tubing in it, and concrete, w/ tile or laminate on top - does this make sense?
Gooserider
