What Size Space Heater for 150 Square Feet?

A 150 sq ft room with average insulation and an 8 ft ceiling needs about 1,500 W of heat (5,118 BTU per hour), which is one 1,500 W heater. Running it flat out costs $0.26 an hour at $0.17 per kWh.

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Heater size needed

1,500 watts

In BTU per hour: 5,118 BTU/hr
1,500 W heaters needed: 1 heaters
Room area: 150 ft²

Running cost at full output

Cost per hour: $0.26
Cost per 8 hours: $2.04

A thermostat cycles the heater on and off, so real running cost is usually lower than full output. Plug 1,500 W heaters straight into a wall outlet, not an extension cord, and keep them clear of anything flammable.

Before you buy: round up to whole packs, check the size printed on the label, and add a little spare. Your supplier has the final say.

Heater watts for 150 sq ft, by insulation and ceiling height

A 150 sq ft room is a typical bedroom or a small den, and is the size a standard 1,500 W heater is usually rated for. The rule of thumb is about 10 W per square foot for an average room, 8 W for a well-insulated one and 12 W for a drafty one, scaled up for ceilings over 8 ft.

Insulation	8 ft ceiling	9 ft ceiling	10 ft ceiling	1,500 W heaters (8 ft)
Well insulated	1,200 W	1,350 W	1,500 W	1
Average	1,500 W	1,688 W	1,875 W	1
Poor or drafty	1,800 W	2,025 W	2,250 W	2

What it costs to run, at $0.17 per kWh

The cost of 1,500 W for 8 hours a day, 30 days a month. Change the price to your own rate in the electricity cost calculator.

How it runs	Per hour	Per 8-hour day	Per month
Flat out (no thermostat)	$0.26	$2.04	$61.20
Thermostat, cold room	$0.19	$1.53	$45.90
Thermostat, cycling about half the time	$0.13	$1.02	$30.60

One heater or more for 150 sq ft?

One standard 1,500 W heater covers 150 sq ft at average insulation, since the room needs 1,500 W. It draws 12.5 A on a 120 V outlet, so plug it straight into the wall and keep other big loads off that circuit.

Choose a heater with a thermostat, tip-over and overheat protection, and keep it 3 ft from bedding and curtains. The space heater sizing guide covers the types of heater, and the running cost guide compares prices.

Want to change anything else? The calculator above is the full Space Heater Size Calculator: edit any number and the results update instantly.

Tools & materials for this project

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Ceramic space heater Oil-filled radiator Draft stopper Window insulation film Smart thermostat

Frequently asked questions

What size space heater do I need for 150 square feet?

About 1,500 W (5,118 BTU per hour) for a room with average insulation and an 8 ft ceiling. A well-insulated room needs 1,200 W, and a drafty one 1,800 W.

How many 1500 watt heaters for 150 sq ft?

1 at average insulation. In a drafty room with 10 ft ceilings it is 2.

How much does it cost to heat 150 sq ft with a space heater?

Running 1,500 W flat out at $0.17 per kWh costs $0.26 an hour, $2.04 for an 8-hour day and $61.20 a month. With a thermostat cycling about half the time it is closer to $30.60 a month.

Related sizes and guides

Related sizes

Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.

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