Electric Heater Sizing Calculator
kW of electric heating for a room from volume, insulation and design temperature lift.
Resistance heat is 100% efficient but expensive per kWh — this same number halves (or better) with a heat pump at COP 2–4.
Formula
Electric Heater Sizing Calculator is a free heater size calculator for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Electric Heater Sizing Calculator
kW of electric heating for a room from volume, insulation and design temperature lift. The calculation implements P = V × (1.2–2.6 W/m³·K by insulation) × ΔT (CIBSE Domestic Heating Design Guide (simplified)). Resistance heat is 100% efficient but expensive per kWh — this same number halves (or better) with a heat pump at COP 2–4.
How to use Electric Heater Sizing Calculator
- 1Enter Room volume in m³.
- 2Enter Temperature lift (in − out) in °C.
- 3Enter Insulation quality (1 good · 2 average · 3 poor).
- 4Read Heater size, Watts per m³ instantly — no submit button needed.
- 5Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Electric Heater Sizing Calculator?
- ✓Implements the standard formula — P = V × (1.2–2.6 W/m³·K by insulation) × ΔT
- ✓Reference cited on-page: CIBSE Domestic Heating Design Guide (simplified)
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Electric Heater Sizing Calculator use?+
It computes P = V × (1.2–2.6 W/m³·K by insulation) × ΔT, per CIBSE Domestic Heating Design Guide (simplified). The formula is displayed under the result.
What should I keep in mind when using this calculator?+
Resistance heat is 100% efficient but expensive per kWh — this same number halves (or better) with a heat pump at COP 2–4.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Electric Heater Sizing Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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