How to Pick the Perfect Size Space Heater for Your Room | NewAir

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NewAir Space Heaters are a reliable way to heat your home, but the wrong size unit can cause some major headaches. If it’s too small, it won’t be able to generate enough heat and it’ll drive up your energy costs as it strains to warm a space beyond its capacity. If it’s too big, you’ll be paying for extra heating capacity you never use. In order to pick the perfect size space heater for your room, you’ll need to take into account several factors, including the degree of insulation, the ceiling height, the windows, and the outside temperature. If you’re using the heater to supplement a central heating system, picking the perfect size space heater is even easier. A few measurements, a bit of math, and you’ll be warm through winter.


When determining the right heater size for your room, there are a few terms you need to be familiar with.

  1. Wattage (Watts). Watts measure the rate of energy transfer in a device: one joule of power per second. The wattage of an appliance is determined by multiplying its amperage (the amount of electricity the machine uses during operation) and its voltage (the electric pressure required to move a charge between two points). All NewAir Space Heaters have a maximum wattage of 1500, except the NewAir AH-400 Portable Oil Filled Space Heater, which has a maximum wattage of only only 400.
  2. BTU (British Thermal Units). BTUs are a standard unit of measurement in air conditioners and heaters. They’re the amount of energy required to raise or lower the temperature of a pound of water by one degree Fahrenheit. In air conditioners, they measure cooling capacity or the amount of energy being removed from the air. In space heaters, they measure heating capacity or the amount of energy being added to the air. One watt equals approximately 3.41 BTUs.
  3. R-Value. An object’s R-value measures its degree of thermal resistance. The higher it is, better is insulates. The recommended R-value for the walls and ceiling of a room depends on the region where you live. Rooms in extremely cold regions have a recommended R-value of 13-21 in the walls and 49-60 in the attic, while rooms in the warmest regions have a recommended R-value of 13-15 in the walls and 30-49 in the attic. Click here to learn the recommended R-value for your home.
  4. Temperature Rise. Temperature rise is the difference between a room’s actual temperature and your desired temperature. It’s an important factor in supplemental heating, as it indicates the amount of energy a heater requires in order to raise the ambient temperature to a comfortable level.

How to Estimate Space Heater Size

Picking the perfect sized NewAir Space Heater depends on several factors, but they’re all built around one basic precept: 10 watts per square foot of space. A 10 ft. x 12 ft. room, for example, requires a 1200 watt space heater (120 sq. ft. x 10 = 1200 watts). This is the quickest and easiest way to size a space heater, but unfortunately, there are a number of factors that can throw it off and have to be taken into account.


Heavily insulated rooms (with approximately double the recommended R-value) require less power to heat them, only 7.5 watts per square foot. Lightly insulated rooms (with approximately half the recommended R-value) require more, roughly 12 watts per square foot. Rooms without any insulation at all – typically garages, basements, and work sheds – aren’t well suited to NewAir Space Heaters. The high degree of heat transfer these rooms experience drains the heat away faster than it can be generated. If you spend a great deal of time in these sorts of areas, consider improving its R-value (read How to Reduce the Energy Costs of Your Garage Heater for tips how) or purchasing a NewAir Garage Heater, which are designed to keep you warm in these types of exposed environments.

Ceiling Height

NewAir Space Heaters work according to the principle of convection. When they’re activated, the air in contact with them heats up and expands upwards, forcing the cooler, denser air above it to sink down and replace it. As the cool air sinks, it comes into contact with the heater and is warmed in turn. As it rises, it displaces more air, continuing the cycle and creating a convection current that gradually raises the temperature of the room. Convection heating is less effective in rooms with high ceilings, anything above 8 feet tall. Hot air gathers there and takes longer to circulate back down to warm the occupants below. To compensate, increase the wattage of your space heater an extra 25 percent for every 2 feet of extra space. For example, a 10 x 12 room with 10-foot ceilings would require a 1500 watt space heater.

1200 watts * 0.25 = 300 watts

 300 watts + 1200 watts = 1500 watts

And a 10 x 12 room with 12-foot ceilings would require an 1800 watt space heater

1200 watts * 0.5 = 600 watts

600 watts + 1200 watts = 1800 watts


Windows are poor insulators, even the best ones. Windows make up approximately eight percent of a typical home, but are responsible for up to 25 percent of its heat loss. The cause is a property known as thermal emissivity. Emissivity measures how effective a material is at emitting thermal radiation. A high rating means they absorb heat. A low rating means they reflect it. Window glass has an emissivity rating of 0.91, so they absorb and emit over 90 percent of the thermal energy they’re exposed to.

NewAir AH-470 Flat Panel Micathermic Space Heater

As the convection currents from your space heater makes contact with the window glass, it absorbs the energy in the air and radiates it out into the external environment. As the air loses energy, it condenses and sink towards the floor, pulling in warm air after it that’s cooled and condensed in turn, creating a secondary convection current that starts pulling heat out of your home. Air is also lost through cracks and gaps in the weather stripping around the frame, which allows warm air to seep out of your home and through infrared radiation – electromagnetic heat waves emitted by people and objects. Infrared radiation is absorbed by walls and furniture, but not by glass, which lets it pass straight through.

The only way to compensate for this persistent heat loss is to lower the U-value of your windows (U-value is the opposite of R-value. It measures how well materials transfer thermal energy) or increase the wattage of your space heater. How much is difficult to estimate because it depends on the size, number, and quality of the windows in question, but a room with a large number of large windows may require an increase of fifty percent or more. Check the U-value of your windows and the integrity of your weather stripping. The better they are at trapping heat, the less additional wattage your heater requires.

Outside Temperature

The degree of heat loss your home experiences is not only dependent on its construction, but also its environment. No home is 100 percent energy efficient, but homes located in extremely cold regions, where the temperature regularly falls to around 20°F, will lose heat at a higher rate than homes in warm or mild regions. If you live in such an area, increase the wattage ratio from 10 watts per square foot to 15 watts per square foot when you’re estimating space heater size.

Supplemental Heating

One of the most common uses of space heaters is to supplement existing heating systems in homes and offices. Because the amount of warm air produced by a central heating system is based on the average temperature of the entire building, they often create under heated areas. The cause may be drafts, high ceilings, poor insulation, large windows, poor ventilation, or just heavier exposure to the weather outside. If increasing the temperature setting on the furnace isn’t practical – it may, for instance, over heat the rest of the building – a NewAir Space Heater is your best option.

Calculating the amount of heat necessary to raise the temperature of a space by a few degrees is more complicated than estimating the size of the heater required for a given room. First, you need to determine the necessary temperature rise by subtracting the current temperature from the desired temperature. If the room is 60°F and you want it to be 70°F, the temperature rise would be 10°F. Next, measure the volume of the space you want to heat (length x width x height). This may be the entire room or just the area around your desk. The average bedroom, for instance, is 12 ft. x 12 ft. x 8 ft. and contains 1152 cubic feet of air. It takes 0.24 BTUs to heat one cubic foot of air by one degree Fahrenheit, so to figure out how many BTUs it would take to raise the temperature of the average bedroom to your desired level, you would multiply the room’s volume by 0.24 and the desired temperature rise.

Volume * 0.24 * Temp. Rise = BTU

Using the example above (12 x 12 bedroom, 10°F temperature rise), the formula would be:

1152 * 0.24 * 10 = 2765 BTU

To convert that figure into watts, divide by 3.41.

2765 BTU/3.41 = 811 watts

So the minimum space heater size you’d need is 810 watts. Like most space heaters, NewAir Space Heaters have programmable temperature settings that allow you to adjust the amount of heat they produce, so if you can’t find a heater with exactly the right power, your best option is to choose a heater with a slightly higher wattage and dial back its heat production to a comfortable level.

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