What size space heater for a home office?
A home office of about 100 sq ft needs roughly 1,000 W, so a 1,000 W heater. A small 750 W heater under the desk is often enough.
Method: About 10 watts per sq ft, the standard rule behind the 1,500 W = 150 sq ft guideline, adjusted for insulation and ceiling height.
Heater power needed
1,000 W
3,412 BTU/h for 100 sq ft
| Power needed | 1,000 W |
| Heat output | 3,412 BTU/h |
| 1,500 W heaters | 1 |
- • Plug heaters straight into the wall, never an extension cord or power strip, and don't share the circuit with other big appliances.
- • A space heater warms the room it's in. It's for supplemental heat, not for heating a whole house.
Space heater size chart
Based on 10 watts per sq ft, an 8 ft ceiling and average insulation.
| Room size | Power needed | Heater to buy |
|---|---|---|
| 100 sq ft | 1,000 W | 1,000 W |
| 150 sq ft | 1,500 W | 1,500 W |
| 200 sq ft | 2,000 W | 2 × 1,500 W or 240 V |
| 300 sq ft | 3,000 W | 2 × 1,500 W or 240 V |
| 400 sq ft | 4,000 W | 3 × 1,500 W or 240 V |
How the calculation works
The standard rule is about 10 watts per square foot, so a 1,500 W heater warms about 150 sq ft. This calculator uses 8 W per sq ft for a well-insulated room and 12 W for a drafty one, and scales up for ceilings above 8 ft. Plug-in heaters stop at 1,500 W because that is the most a standard 15 A outlet can safely supply.
More space heater guides
Frequently asked questions
What size space heater for a 200 sq ft room?
About 2,000 W by the 10 watts per sq ft rule. That is more than a single plug-in heater, so use two heaters or a 240 V wall heater, or accept slower heating from one 1,500 W unit.
Is a 1,500 W heater enough for a bedroom?
Yes for most bedrooms up to about 150 sq ft. It is also the largest size that plugs into a normal outlet.
Are more watts better?
More watts means faster heating and more electricity. Bigger than you need just cycles on and off.
Which is cheaper to run, a space heater or central heat?
A space heater is cheaper only if it lets you turn the rest of the house down. Heating one occupied room can save money. Heating everything with them does not.