Propane for a Season Calculator
Work out the propane gallons, tank refills and cost a whole heating season needs from your furnace load and run hours.
How it works
season BTU = heat load × run hours/day × days · gallons = season BTU ÷ (AFUE × 91,500 BTU/gal) · refills = ⌈gallons ÷ usable tank⌉
Propane delivers about 91,500 BTU per gallon — roughly a third less than heating oil — so a propane season burns more gallons for the same heat. The furnace’s AFUE sets how much of each gallon actually warms the house. Because tanks are only filled to about 80% for safety, a 500-gallon tank gives roughly 400 usable gallons per fill, which is what sets how many deliveries the winter takes.
Worked example
A 30,000 BTU/hr load running 14 h/day for 150 days is 63 million BTU. At 90% AFUE each gallon yields 0.90 × 91,500 ≈ 82,350 usable BTU, so 63M ÷ 82,350 ≈ 765 gallons. That’s two fills of a 400-gallon-usable tank and about $1,913 at $2.50/gal.
Sources: Propane - Wikipedia
Frequently asked questions
Why does propane use more gallons than oil for the same house?
Propane holds about 91,500 BTU/gal versus 138,500 for heating oil — about 34% less energy per gallon. For identical heat you burn roughly 1.5× the gallons, though the price per gallon is usually lower.
Why can’t a 500-gallon tank hold 500 gallons?
Propane is stored as a liquid that expands with temperature, so tanks are filled to about 80% to leave a vapor cushion. A "500-gallon" tank therefore delivers roughly 400 usable gallons per fill.
Should I lock a price or fill in summer?
Propane is usually cheapest in the off-season (summer) when demand is low. Pre-buy or budget-plan contracts can smooth the cost, but read the cap and fee terms before signing.
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This calculator is for educational purposes. Double-check important results before acting on them.