What Size Room Will A 1500 Watt Heater Heat?

One of the most important factors in deciding on the size of a room for a 1500-watt heater is how big the space is. The first step, then, is to measure your living room or bedroom. If you have an open floor plan with no obstructions, any large area will do. 

However, if walls and furniture are blocking your heat source from reaching all areas equally, you may need to purchase a larger unit that can handle more square footage.

What Size Room will a 1500-watt Heater Heat?

A 1500-watt heater that produces approximately 5,100 BTUs will heat most rooms to around 150 to 200 sq ft. 

This is equivalent to a 10 by 15-foot room. If you have an average-sized bedroom, it should be able to keep the room warm for a few hours without issue.

Is 1500 watts a Lot of Electricity?

No, it’s not “a lot.” But the wattage that a 1500-watt heater uses is quite high. In fact, it uses almost double the amount of electricity as a toaster oven! 

Is a 1500-watt Heater Good?

A 1500-watt heater is not the best heating option for a larger room that you want to heat. This type of space heater typically does not have the power needed to effectively warm larger spaces, which may result in uncomfortable conditions throughout your home. A more powerful model should be selected if you want an effective solution.

Do All 1500-Watt Heaters Heat the Same?

No. The size of room a 1500-watt heater can heat depends on the design and insulation. Most models are not built to be adequate for larger spaces. However, some may provide you with enough warmth if installed in smaller rooms or areas which are colder than others. 

To find out how much area your 1500-watt heater can warm-up, use this formula: 

Measure the length x breadth (in feet) = square footage. 

A minimum 400-watt unit will keep about 100 sq ft warm. 800 watts would do 150 sq ft and 1200 watts about 200 sq. ft., etc.

How Many BTUs is 1500 Watts?

A kilowatt-hour (kWh) is a unit for measuring energy or the amount of work done. One BTU equals about 0.293-watt-hours. 1500 watts = 1500 x .000293 kWh = 430123 Wh/hr.

How Hot Does a 1500-Watt Heater Get?

1500 watts is the equivalent of 1800 BTU per hour. With the 120-volt, 1,500-watt heater, you can easily heat small spaces. 

The good thing about it is that it can heat a tiny space quickly and efficiently. It generates 1,500 watts of power each hour and heats up to 5,100 BTUs of air.

How Long Does It Take for a Space Heater to Heat a Room?

A 1500-watt heater can heat a room in about 15 minutes. The space must be at least 100 square feet to ensure it heats the entire area and doesn’t leave any spots chilly or colder than others.

If the space is more than 100 square feet, it may take longer to heat. It also depends on how insulated the room is and what its temperature was before heating started.

If you have a space heater that uses more than 1500 watts, then it won’t take long to heat the room because it has a higher wattage.

How Many Watts Per Square Foot for Electric Heat?

When sizing an electric heater, it is highly recommended that the unit should use 10 watts of power per square foot of heated space.

This is because one watt of power produces 3.4 BTUs of heat. Therefore, 10 watts of power equal to 34 BTUs of heat output for each square foot of room surface area.

If you have to replace your old heater, it’s better to get a replacement with the same wattage as the one you had before.

The heating performance of your heater is determined by the characteristics of your room. If your space has a north-facing wall, lacks insulation, and has a lot of draughty windows, the heater may not be appropriate.

Another reason is the shape of your room. If your area has a distinct form, this may impact air circulation and cause some areas to be colder than others. For example, large bookcases might cause this issue.

Space Heater Sizing

Sizing a space heater is tremendously important because it will help you purchase one that will suit your needs. You need to buy a room heater that is well rated for the approximate square footage or dimensions of your space. Check out below what you need to know.

Why Heater Size is Important

The National Electric Code requires home electric space heaters to have a maximum capacity of 0.9 horsepower and a minimum capacity of 0.5 horsepower (1 hp). If your space heater has greater output, it will use more energy and cause higher utility costs. 

Buying a space heater that is too tiny, on the other hand, will not adequately heat your area. Therefore, you need to find the right balance between the space heater and the size of your space.

Space Heater Square Footage Equation

Determine the perfect sizing by calculating the heater wattage output. For every square foot of floor surface area in the space, you’ll need roughly 10 watts of heating power as a rule of thumb.

When it comes to heating, a 1,500-watt heater can provide enough heat for a 150-square-foot space.

If it’s only used as a supplement to another heating source, though, it covers a considerably larger surface.

Space Heater Sizing Chart

Square Footage of Your Space Watts
75 sq. ft. 750 watts
100 sq. ft. 1,000 watts
125 sq. ft. 1,250 watts
150 sq. ft. 1,500 watts
200 sq. ft. 2,000 watts
250 sq. ft. 2,500 watts
300 sq. ft.  3,000 watts
350 sq. ft.  3,500 watts
400 sq. ft. 4,000 watts


Factors to consider when sizing a space heater

There are several factors you need to consider when sizing a space heater. Below we’ll go over those factors to help you understand them better.


Rooms that are heavily insulated (with an R-value of approximately double the recommended amount) require less power to heat. They require only 7.5 watts per square foot. 

Lightly insulated rooms (with an R-value of approximately half the recommended amount) need more, about 12 watts per square foot. 

Rooms without any insulation at all like Garages, basements, and work sheds aren’t usually well suited for various space heaters.

The high amount of heat transfer that these rooms experience rapidly removes the heat they produce. 

Consider enhancing the R-value or buying a space heater designed to keep you warm in such exposed settings if you spend a lot of time in these sorts of places.

Ceiling height

Convection is a basic principle of many space heaters. When they’re switched on, the air in contact with them heats up and expands upwards, forcing the colder, denser air above it to sink and be replaced. 

As the chilly air sinks, it comes into touch with the heater and is warmed.

As it rises, it displaces more air and continues the cycle, generating a convection current that gradually heats the space. Convection heating is less efficient in rooms with lofty ceilings.

It’s the same reason why chilly air takes longer to rise in a basement apartment. The cold air lingers there for longer, slowing down the circulation of warm air back down into the space. 

You can increase the wattage of your space heater by 25% for every 2 feet of extra height to make up for it. A 1500-watt space heater would be required in a 10 x 12 room with 10-foot ceilings.

A 10 x 12 room with a 12-foot ceiling requires an 1800-watt space heater.

1200 watts x 0.5 = 600 watts

600 watts + 1200 watts = 1800 watts


Even the best windows are ineffective insulators. Windows account for approximately eight percent of a home’s total surface area, but up to 25% of its heat loss. 

Thermal emissivity is the term used to describe this property. Emissivity is the measure of a material’s ability to radiate thermal energy. 

A high rating implies they absorb heat; a low rating implies they reflect it. Because window glass has an emissivity value of 0.91, it absorbs and emits 90% of the thermal energy it receives.

Outside Temperature

The amount of heat loss your house suffers is not only determined by its construction, but also by the environment in which it is located. 

Although no home is 100% energy efficient, homes in very cold areas where the temperature drops to around 20°F regularly will lose heat at a greater rate than houses in warm or moderate regions. 

If you reside in such an area, when measuring space heater size, go up from 10 watts per square foot to 15 watts per square foot.

Supplemental Heating

It’s more difficult to determine the amount of heat needed to raise the temperature of a space by a few degrees than it is to calculate how big a heater will be required for a certain room. 

To begin, subtract the present temperature from the desired temperature and then determine what temperature rise is required. 

The 10°F temperature difference between 60°F and 70°F would result in a volume increase of 50%. Then measure the area you want to be warmed (length x width x height).

This might be the whole room or just a small section surrounding your desk. A typical bedroom, for example, is 12 ft. x 12 ft. x 8 ft. and has 1152 cubic feet of air. 

To determine how many BTUs, it will take to raise the temperature in the average bedroom to the desired level, multiply the space’s volume by 0.24 and the desired temperature increase.

Best 1500-Watt Space Heater

PELONIS PH-19J 1500W Space Heater


  • It comes with widespread oscillation function
  • The heater is quite safe to use
  • It provides fast and efficient heating
  • Equipped with programmable thermostats for optimal heating temperature


  • Unfortunately, the item is not durable enough as one would expect
  • It may cause a fire because the cord tends to heat a lot when functioning

The PELONIS space heater is designed to work fast and efficiently. It features a compact size and can work excellent as a personal heater. 

You get two heating options, which are the high and low modes that help you achieve a comfortable temperature with maximized efficiency.

Thanks to its special design, you can use this space heater wherever you are such as in your office or bedroom. This space heater can easily increase the heat dissipation by 20 percent more than other heaters. 

Therefore, it’s worth checking it out to see if it can comfortably suit your needs.

1 thought on “What Size Room Will A 1500 Watt Heater Heat?”

  1. Hello. I was looking for the way to figure out what size space heater I need. This article should be very helpful. One question: I always thought square footage formula was length x width. Period. Never heard of dividing it by two. I looked it up, and l x w is the standard formula. What am I missing here? You give a different formula. Thx for your time.

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