Isnt the heat loss calculated at something like the 90% factor temperature.. like where the temp is higher than that point, 90% of the time (in the heating season) ?
Anyhow.. Im still reading this thread (Im not a post and vanish kind of guy).. Im just having a hard time finding that 'design temp' for this area to redo my loss. Nothing via google yet, but Ill keep looking. (Its Thunder Bay, Ontario in case someone has a table etc).
So, for -24F, the Slantfin app says I need 75000 btu/h.
My avg oil use seems to be about 2400L, or 87Mbtu (and at 80% eff 70Mbtu actual heat.) (heh,i forgot to incl my actual energy used in my first post).
So, is it possible to say set up a graph, with one axis +65 to -24 (or hdd's), and the other axis 0-70.. ? What shape would the line be ? Sunny days like you say would put you lower (btu input required) than the line and cloudy or night would push you above it ?
Actually, now that i think of it.. the higher the required input (high hdd's / low temp), the more the boiler is running and the more efficient it is (less standing stack loss too).
Sorry if Im gettin kinda weird on yas.. this stuff interests me.