FBWNDR wrote:

At a
very rough guess, I would assume a 3000 square foot house in the
midwest would require at least 100,000 BTU/hr furnace, probably a
little larger.

"A 3000 square foot house" has no meaning unless you know what the
outside temperature is. It may be a 'true', but useless number.

Your calculation is a real interesting approach.

--
bud--