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calculating BTU output for liquid fuel furnaces
#1 Posted : Thursday, October 24, 2013 3:31:54 PM(UTC)
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Does anyone know of a good way to "clock" a furnace if it is propane, kerosene or oil for btu ouput rating? this is needed for an accurate weatherization assistance audit, but often the nameplate is missing from the furnace. I have been searching the web a bit but so far not much help. Thanks!
Tim Lenahan
#2 Posted : Thursday, October 31, 2013 2:56:25 PM(UTC)
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You can get an estimate of the btu/hr input for oil and kero by looking at the burner nozzle size which is in gals/hr. This number is good for a pump pressure of 100 psi and most burners run 140 psi so you need to adjust the nozzle flow accordingly with charts supplied by the nozzle manufacturers. A .75 gal/hr nozzle flows at .89 gal/hr at 140 psi. Multiple that by the heat content per gallon to get the btu/hr input. Multiple your steady state efficiency for the output.

For propane, use the rating on the heating system label as there is less chance the orifices have been changed. Use your actual steady state efficiency to adjust for the output.

You should be close enough for your audit inputs.
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