How to Use the Electric Heater Sizing Calculator
An undersized heater takes forever to reach the target temperature, while an oversized one wastes electricity and adds overheating risk. This calculator takes your space's length, width, and height along with the desired temperature rise (°F) and insulation level to estimate the required heater capacity in kW and BTU/hr.
It uses a practical rule-of-thumb formula — volume x temperature rise x a heat-loss coefficient — applying a lower coefficient for well-insulated spaces and a higher one for poorly insulated spaces, since poor insulation needs more capacity to hit the same temperature rise.
This is a steady-state estimate; real-world capacity needs also depend on air infiltration around doors and windows, ventilation rate, and desired warm-up time. For industrial or commercial spaces, run a full heat-load calculation or consult a mechanical/electrical engineer before finalizing equipment.
Frequently Asked Questions
Pick Good for new or well-insulated construction, Average for typical existing buildings, and Poor for spaces with heavy outdoor exposure, like warehouses or temporary structures. Poorer insulation needs more heater capacity for the same temperature rise.
Yes. This is a steady-state heat-loss estimate, so adding a 10-20% margin is common practice to account for door/window infiltration and faster warm-up times.