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Hello all - fantastic site you guys have here - immensely informative, nice community - a really great find. I'm a newbie to this, not a professional in the heating/comfort industry(a scientist/doctor type, actually), but I love learning and am pretty handy, and I'm trying my hand at designing a radiant hot water system for my house. I've got Siegenthaler's book (and have been doing the problems!), and I've been reading the Idronics semiannual publications, reading the installations manuals for Triangle Tube and Viessmann modcons, essentially reading reading reading all I can.
I'm starting out with a heat loss calculation, as advised. I'm wondering if any have come across this site:
It seems to actually calculate UxAxdT, and takes into account different building materials and windows and such, as well as air infiltration, and I'm getting numbers that seem to make sense.
I have a 105 year old frame house in Seattle, some insulation and window upgrades, but we still have some big singe-pane bay windows with that cool old wavy glass that I just don't have the heart to rip out - however they leak heat like a sieve.
(Presently we have gas forced air, the plant at the end of its life and needing replacing.) The house has about 700 sq-ft on the first and second floors, and the same size heated basement.
From the builditsolar.com site calculator, I'm getting a total heat loss of 46870 BTU/hr. When I look at my gas bill over the past year, the biggest monthly use was 7.5 therm/day this past February - or 31250 BTU/hr on average. I went back and looked at daily temps around here that month, and on only two days did we get down to the design temp of 20'F. On average we were 38.3'F for the lows - or about 18.3'F higher than design temp. I took the dT at design (68-20) and the dT that month (68-38.3) and ratio'd them and got 0.62. Dividing the ave BTU/H that month (31250) by this ratio (0.62) and I get 50400 - which agrees pretty closely with the prior calculation.
Am I on the right track?