I'm getting lost in your calculations, but I have 21392 cubic feet in the house. I attempted to get my gas usage numbers from the online bill pay, but what I can access right now does not include Oct04-Feb05, which are going to be the ones that really count. I should be able to get them tomorrow during business hours and will post gas usage then.
I'm not sure if I'm ridiculously off on my load calc, or if the equipment is ridiculously off. It wouldn't be the first thing about the house that was half-a**ed.