a follow-up:
Quote:
The heat*producing capacity of fuel products is measured in British thermal units (Btus). A Btu is the amount of heat required to raise
the temperature of one pound of water by one degree Fahrenheit. One gallon of no. 2 heating oil contains approximately 138,000 Btu.
One gallon of no. 6 residual fuel oil contains approximately 148,000 Btu. The Btu content of no. 4 fuel oil depends on the percentages of
the distillate and residual components of the blend, but is commonly 143,000 Btu per gallon. Thus, all other factors being equal, a build*
ing will require less no. 6 oil than no. 4 oil or no. 2 oil to heat the same amount of space because it has the highest Btu content per gallon.
The higher the Btu content of the fuel, the less of it you need attain the same results.
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I won't vouch for the credibility of this source, but here's the URL:
http://www.castleoil.com/content/media/pdf/MannRpt200610.pdf
They are claiming a 7.2% higher BTU content of #6 than #2, and a 3.6% higher BTU content of #4 than #2... I'd go with the #4 because it should be run-able in a SVO system, but I'd worry about heating the #6... they need fairly high temperatures to run it effectively... over 200°F if I remember correctly.