Specific heat matters
The default specific heat of 1 fits liquid water in common HVAC-style estimates. Other materials need their own specific heat values.
Example
Heating 100 lb of water by 20 F with a specific heat of 1 requires about 2,000 BTU in an ideal calculation.
How to use the result
Use the estimate for simple heat-energy comparisons. Real heating systems need more energy because of losses, equipment efficiency, standby time and surrounding conditions.
Limitations
This calculator does not size HVAC equipment by itself. Building load, insulation, air leakage, climate and equipment efficiency all matter.
Last reviewed: 2026-05-17