Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: hondaracer2oo4 on December 10, 2016, 06:20:35 PM
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So I am interested in trying to figure what exactly I am using for real btus to heat my house. So I think I have the calculations right, someone please correct me if I am wrong. So I have a g200 which holds 200 gallons. If I am correct to find out how many btus are available at 180 degrees the calc is 200x8.33x180=299,880 btus. So I have timed how long my blower in the house runs for. It runs for typically 7.5 minutes at a shot. After the blower runs the boiler loses approx 3 degrees. So if my calc is correct that means that 200x8.33x177=294882. If we deduct 299880 from 294882 we get 4998 btus used every time the furnace runs. If we break it down further to btus used per minute we would divide 4998 by 7.5=666.4 btus per minute. Right now it's 15 degrees out and the fan is running 7.5 minutes on and 11.5 minutes off. So that means more or less the blower is running 22.5 minutes per hour. So 22.5x666.4=14,827 btus used per hour. Now that seems awful little btus used per hour to me??? My house is 2800 sqft and is 220 years old. I have I insulate apps and air sealed well but it still seems awful low on the btus per hour. I know my Woodstock fireview wood stove which should be putting out around 30k btus per hour at least can no way handle heating the house at these temps we have right now. I know that air isn't moving like the forced hot air is but still??
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You can skip the 180 from your equation and just multiply by the temp drop instead. You should get the same numbers.
The problem with trying to calculate by water btu capacity is that the boiler itself (steel, refractory, ashes, etc) is storing heat and there is most likely some amount of heat being generated even while the stove is idling.
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Good point on just multiplying the temp drop. Are you saying that the btus used are actually greater than the 3 degree drop I see because the temp of the boiler itself radiates some and keeps the final temp of the water higher than it actually should be?
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Yes, at least some.
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Ya, i think some heat gets radiated from the boiler between cycles. My Central Boiler has a thermocouple in the secondary burn chamber. If you have a good coal bed it can still be 400-500 degrees in there 1\2 hour after it reached its set point and shut off.
Plus, if your pump runs continuous, then the heat exchanger and pex lines in the home are still radiating heat into the home between furnace cycles. I know in my house, if its above 40 degrees, the furnace rarely comes on. Just having the hot water circulating through the lines and heat exchanger dumps enough heat into the home to keep it warm.
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I think my numbers may be closer to correct than I initially thought. I looked at equivalent for oil. Oil has 138k btu per gallon. At 75% efficiency that brings it down to 103k btu per gallon. If I needed 18 k btu per hour x 24 hours= 432000 per day. 432000/103000= 4.1 gallons of oil per day x 1.89 = $7.88 per day x 30 days=$245 per month. Appears somewhat low still but maybe not.
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It could be close. The heat loss from the boiler and underground pipe would offset some of the thermal storage of the boiler itself.
I think fuel oil has lower BTU content since they switched over to ULSD. I have heard 125k BTU but not sure if that is correct.
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I think fuel oil has lower BTU content since they switched over to ULSD. I have heard 125k BTU but not sure if that is correct.
Thats odd, supposedly waste oil has roughly 160,000 BTU per gallon.
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I was taught that heating oil has 144,000 BTU's per gallon.
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Not sure about the calculations you used hondaracer but it is very hard to calculate in all the variables associated with wood burning. The fire box is continually radiating heat unless it goes out. Heat loss in the lines and boiler itself and is your home heating the only load on the boiler, no water heating or other buildings?
A house your size would normally be sized for an 80 to 100 BTU rated high efficiency furnace with an approximate 50% cycle time. That would be for a well insulated home and the rating is normally worse case scenario(-15 to -20 temps).
Slim you are correct about fuel oil, normally 144,000 is number we used for a conversion factor when we used to convert fuel oil furnaces or boilers to natural gas. Different # oils have different BTU content as does regular diesel fuel and ULSD.
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Slim you are correct about fuel oil, normally 144,000 is number we used for a conversion factor when we used to convert fuel oil furnaces or boilers to natural gas. Different # oils have different BTU content as does regular diesel fuel and ULSD.
How much the difference you suppose between old school premium diesel and this new ultra low sulfur crap? Never had algae problems until they took the sulfur out, now we treat it all rather than deal with that happy crap again.
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Yea but sulfer AND wood smoke odor are offensive to some people so the government deems it necesary to take our LIBERTY away AGAIN! Of course I bet there was not a cent exchanged?
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I was taught that heating oil has 144,000 BTU's per gallon.
I think it used to be 144K, then when it went to low sulfur it dropped to 139K, then when it went to ultra low sulfur it went to somewhere around 125-129k.
I may be off a bit on the numbers but I think they are around there somewhere.
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Another beautiful thing about burning wood, our fearless leaders can't legislate/ dictate the BTU's out of it.