Sizing electric baseboard
The standard rule is 10 watts per square foot for averagely insulated rooms in a cold climate — this tool lets you shift between 8 and 12.5 W/sq ft for insulation quality and climate. Standard electric baseboard delivers about 250 watts per linear foot, so a 150 sq ft bedroom needing 1,500 W takes roughly 6 ft of baseboard, ideally placed under the windows.
Electrical planning (the part people forget)
Baseboard heaters are permanent loads, so the 80% rule applies: a 20 A / 240 V circuit may carry at most 3,840 W of heater continuously. Practical circuit loads: 15 A/240 V → 2,880 W, 20 A/240 V → 3,840 W. Use 240 V heaters wherever possible — 120 V models draw twice the amps for the same heat and eat circuit capacity fast. Thermostats: line-voltage wall thermostats or smart line-voltage models (double-pole preferred, they fully disconnect).
| Room | Watts (avg insulation) | Baseboard length |
|---|---|---|
| 10×10 bedroom (100 sq ft) | 1,000 W | 4 ft |
| 12×14 bedroom (168 sq ft) | 1,700 W | 6–7 ft |
| 15×20 living room (300 sq ft) | 3,000 W | 12 ft (2 units) |
Frequently asked questions
How many watts of baseboard heat per square foot?
Use 10 W/sq ft as the baseline for average insulation in a cold climate; 8 W for well-insulated rooms and up to 12.5 W for drafty older rooms or very cold regions.
How many feet of baseboard do I need?
Divide required watts by 250 (standard baseboard output per foot). A 1,500 W room needs about 6 feet — as one long unit or split under two windows.
Can I put baseboard heaters on a regular outlet circuit?
No. Baseboards are continuous loads that belong on dedicated circuits sized with the 80% rule, almost always 240 V. Have an electrician run the circuit.
Are electric baseboards expensive to run?
They are 100% efficient but electricity is a costly heat source — typically fine for single rooms and additions, expensive as whole-home heat compared to heat pumps at 300%+ effective efficiency.