Home Problems
One Room Colder Than the Rest of the House? Causes and Fixes
One room always colder than the rest of the house? Blocked vents, duct leaks, missing insulation and drafts are the usual causes. Here are 9 fixes, cheapest first.
6 min read
Free tool
Space Heater Size Calculator
Enter your room size, ceiling height and insulation to see the space heater wattage you need, in watts and BTU, and how many 1,500 W heaters it takes.
How to use the Space Heater Size Calculator
- Enter the length, width and ceiling height of the room in feet.
- Choose how well insulated the room is and whether it is a cold spot.
- Read the watts and BTU you need and how many 1,500 W heaters that means.
How the space heater size is calculated
Watts needed = floor area × 10 watts × (ceiling height ÷ 8), then adjusted:
| Condition | Adjustment |
|---|---|
| Good insulation | Multiply by 0.8 |
| Average insulation | No change |
| Poor insulation or drafts | Multiply by 1.25 |
| Over a garage, north side or lots of glass | Multiply by 1.2 |
One watt gives off about 3.412 BTU per hour, which is how the BTU figure is worked out. This is a rule of thumb. The best fix for a room that will not warm up is often to find out why, as described in one room colder than the rest of the house.
Pick a safe heater
- Choose a model with tip-over and overheat shutoff.
- Plug it straight into a wall outlet, never a power strip or extension cord.
- Keep it 3 feet away from curtains, bedding and furniture.
- If the breaker trips, read why a space heater trips the breaker.
- Work out the running cost first with the space heater cost calculator or the guide on what a space heater costs to run.
Frequently asked questions
What size space heater do I need for my room?
A common rule is about 10 watts per square foot for a room with an 8 foot ceiling and average insulation. A 12 by 12 foot room (144 sq ft) needs about 1,440 watts, so a 1,500 W heater fits.
How many square feet will a 1,500 watt heater heat?
Roughly 150 square feet in an average room. A poorly insulated room, a high ceiling or a cold location cuts that figure.
Is a bigger space heater better?
No. Most plug-in heaters top out at 1,500 watts because that is what a standard 15 amp circuit can safely carry. A heater that is too big for the room cycles on and off, and one that is too small never catches up.
Can I run two space heaters in one room?
Only on separate circuits. Two 1,500 W heaters on the same circuit will usually trip the breaker, and can overheat the wiring if the breaker fails.
Learn more
Home Problems
Space Heater Keeps Tripping the Breaker? Causes and Safe Fixes
Space heater tripping the breaker? An overloaded circuit is the usual cause. Check what else shares the circuit, try the low setting and know when it's a fault.
3 min read