Every heating-cost comparison starts with one number: how much useful heat (in BTU) your home needs per winter. Get this right and the calculator results are meaningful; guess wildly and they aren’t. Here are three ways to estimate it, from quick to accurate.
Method 1: square footage × a climate band (quick)
Multiply your conditioned floor area by a per-square-foot annual heat band that rises with climate severity. This is what our calculator uses by default:
| Climate zone | Planning band | 2,000 sq ft home |
|---|---|---|
| Mild | 8,000 BTU/sq ft/yr | ~16 MMBTU |
| Mixed | 18,000 BTU/sq ft/yr | ~36 MMBTU |
| Cold | 28,000 BTU/sq ft/yr | ~56 MMBTU |
| Very cold | 38,000 BTU/sq ft/yr | ~76 MMBTU |
It’s a planning band, not a measurement — an old leaky house lands at the top, a tight new build at the bottom.
Method 2: back it out of your bills (most accurate)
If you heat with gas, oil or propane, your bills are a measurement of your home:
- Gas: heating-season therms × 100,000 BTU × AFUE (e.g. 0.95) = delivered BTU.
- Oil: heating-season gallons × 138,500 BTU × AFUE (e.g. 0.85).
- Propane: heating-season gallons × 91,500 BTU × AFUE (e.g. 0.92).
Subtract any summer baseline (water heating, cooking) so you count only space heating. This delivered-BTU figure is the gold standard to feed into a fuel comparison.
Method 3: heating degree-days
For the technically inclined, annual demand ≈ HDD × 24 × (design heat loss ÷ design temperature difference). Local HDD data and a Manual J load calculation give the most rigorous answer — and an HVAC pro will do exactly this when sizing equipment.
Then compare systems
Once you have a heat-demand figure, the calculator prices it across a heat pump, gas, propane, oil and electric resistance at your state’s fuel prices. And remember: the cheapest BTU is the one you don’t need — insulation and air sealing cut demand for every system at once.