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re: jotul stoves?
16 oct 2000
rs191 wrote:
>the castine is 50k btu, the tried-and-true oslo model is 60k btu.
that's btu per hour...
>any ways to figure out the size of the wood stove we should get?
>the only formula i've seen says multiply the cubic feet in your
>house by 4.5 to get the btu needs.
sure. "ohm's law for heatflow," replacing amps with btu/h, voltage
difference with temperature difference, and electrical resistance with
thermal resistance. find the total thermal conductance of your house (g)
and multiply by the indoor-outdoor temp difference on a cold day to find
the heat power needed to keep it warm.
for instance, a 32x32x8' tall house with 80 ft^2 of r2 windows and r10
walls and an r20 ceiling with lots of air leakage, 2 housefuls per hour
(2 ach) has a thermal conductance g = 80ft^2/r2 = 40 btu/h-f for the
windows plus 944/10 = 94 for the walls plus 1024/20 = 51 for the ceiling
plus about 2x32x32x8/60 = 273 btu/h-f for 273 cfm of air infiltration,
a total of 458 btu/h-f. on a 10 f day, it needs (70f-10f)458btu/h-f
= 27,500 btu/h (27.5k btu/h) to stay 70 f inside. on a -10 day, it needs
(70-(-10))458 = 36.6 k btu/h.
with r4 windows and r20 walls and an r40 ceiling and 0.5 ach, g = 161,
so it only needs (70-10)161 = 9,660 btu/h on a 10 f day.
reducing air leakage might be an inexpensive first step, followed by
attic insulation, then walls, then windows.
4.5x32x32x8 = 36.8k btu/h.
nick
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