Quote Originally Posted by JimmyP View Post
That company showed up and did some measurements and came up with 38000 BTU's/ hr heat loss. So a 3 or 3.5 ton system needed.

My electrical utility bill average for Dec to Feb was 1500kw /month this is 170500 btu's day and 12 hours / day ( darkness without solar gain) of usage would be 14208 btu's/hr. There is no way I would need 38000btu's hr.
Maybe he likes to size for -6 'F with an assumed HIGH infiltration rate.
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One needs to review electric usage by the hour if you wish to establish heat capacity required
based on power usage
and equipment heat output
or one must compensate for Heating Degree Days (HDD) versus Design Temperature.

PEAK LOAD might be 1.5 to 2.5 X the Average usage depending of the day, week or month.
For example, Design Temperature = 10'F and Average Temperature = 30'F ( HDD = 65 - 30 = 35)

dT Design = 70 -10 = 60
dT HDD = 70 - 35 = 35
60 / 35 = 1.7

dT HDD = 70 - 45 = 25 for a warmer month, week or day
60/ 25 = 2.4

If your average temperature for Dec - Febr was 30'F ( HDD = 35 * 90 days = 3150),
one would use 1.7 * portion of electric bill used for heating IF electric strip was used.

X C.O.P. if heat pump is used.