Common question: what size stove do I need? Here is one way to answer that question based on my house in northern MN. I picked Dec 25 because we were visiting family and the house was heated with electricity Dec 23-26. We have a separate meter to measure electricity used for heat; normal heat is the wood stove in the living room with open design living room, dining area, kitchen. With the wood stove the open design area is heated to about 70F and two bedrooms, bathroom and hall to the back door are cooler.
Calculate your numbers and plug them in, and you should be able to get a good estimate of the btuh size of stove you need.
Ambient exterior temperature = -15F average on Dec 25
House: 1500 sq ft main level; 1500 sq ft walkout not occupied in winter.
Heat: electric baseboard both levels; main level 60-62F and walkout 50F on Dec 25
kWh used: main level 109, lower level 13, total 122 kWh.
Heat value of kWh = 122 x 3412 / 0.98 = 424,760 btus (assumed electricity efficiency 98%)
Btuh = 424,760 / 24 = 17,700 btuh
Heat loss = 17,700 btuh
Heat value of seasoned wood, assumed 20% MC and 400F stack temperature = 6,050 / lb
Efficiency rating of our wood stove = 68%
Wood needed to heat house to same degree as electric: 17,700 / 6,050 / 0.68 = 4.3 lbs/hr
Wood needed per 24 hrs = 4.3 x 24 = 103 lbs
Size of wood stove needed: heat loss btuh / stove efficiency = continuous btuh stove output required
17,700 / 0.68 = 26,000 btuh continuous output. But wood stove output varies, so I would think that average output under a good burn would be about 50% of maximum rated output.
In my case, the stove is rated at 55,000 btuh on high burn. Using 50% of rated burn btuh as the average btuh: 55,000 x 50% = 27,500. This is slightly more than the calculation, but the calculation only provides what I think is a good estimate in sizing a wood stove.
If you don't heat with electricity: LP btu/gal = 91,333; oil btu/gal = 138,500; NG = 100,000 btu/therm
Comments appreciated.
Calculate your numbers and plug them in, and you should be able to get a good estimate of the btuh size of stove you need.
Ambient exterior temperature = -15F average on Dec 25
House: 1500 sq ft main level; 1500 sq ft walkout not occupied in winter.
Heat: electric baseboard both levels; main level 60-62F and walkout 50F on Dec 25
kWh used: main level 109, lower level 13, total 122 kWh.
Heat value of kWh = 122 x 3412 / 0.98 = 424,760 btus (assumed electricity efficiency 98%)
Btuh = 424,760 / 24 = 17,700 btuh
Heat loss = 17,700 btuh
Heat value of seasoned wood, assumed 20% MC and 400F stack temperature = 6,050 / lb
Efficiency rating of our wood stove = 68%
Wood needed to heat house to same degree as electric: 17,700 / 6,050 / 0.68 = 4.3 lbs/hr
Wood needed per 24 hrs = 4.3 x 24 = 103 lbs
Size of wood stove needed: heat loss btuh / stove efficiency = continuous btuh stove output required
17,700 / 0.68 = 26,000 btuh continuous output. But wood stove output varies, so I would think that average output under a good burn would be about 50% of maximum rated output.
In my case, the stove is rated at 55,000 btuh on high burn. Using 50% of rated burn btuh as the average btuh: 55,000 x 50% = 27,500. This is slightly more than the calculation, but the calculation only provides what I think is a good estimate in sizing a wood stove.
If you don't heat with electricity: LP btu/gal = 91,333; oil btu/gal = 138,500; NG = 100,000 btu/therm
Comments appreciated.
