Choosing the right space heater for the room is important. There are three steps to follow in order to know what you'll need to get the room warm.

  1. Determine cubic foot volume for the room to be heated (length x width x height of the room = cubic foot).
  2. Find your heating zone on the sizing chart below.
  3. Determine the BTU/HR by multiplying the cubic volume by the heating factor from the sizing chart (Heating Factor x Cubic Feet = BTU per Hour).
    1. The exception here is Zone 5. See below.

Here's an example to help clarify:

Say that you would like to provide additional heat for a 20' long by 15' wide by 8' high room that is located in Richmond, VA. So multiply 20 x 15 x 8 to get the answer of 2400 cubic feet (length x width by height = cubic feet). Next, locate Richmond on the Sizing Chart below (that would be Zone 4).

Now you'll need to figure out how much BTU per hour you'll need. Notice in the Heating Factor chart below that Zone 4 has a heating factor of 7.5. So multiply 7.5 x 2400 to get 18,000 BTU per hour (Heating Factor x Cubic Feet = BTU per Hour).

Look up 18,000 BTU/Hr in the Vent-Free Heater Chart below and you'll see that an SR18, SR18T, or an HR18 is the space heater you want to warm the room sufficiently.

Chart of the United States showing sizing chart by region.

Heating Factor Chart
Zone Heating Factor
1 4.0
2 4.8
3 5.5
4 7.5
5 See Below

Getting the BTU for Zone 5

Say your house is of average construction, and you want to use a thermostatically (TStat) controlled vent-free space heater. Find your Heating Factor using the chart below. Then take the cubic feet from the example above (2400) and multiply it by the heating factor from the chart (4.05) to get your BTU/HR (9720) or Cubic Feet x Heating Factor = BTU/HR. This is the maximum BTU output of a vent-free heating appliance for this room so you would need the SR6, HB06, or HR06 space heater.

Heating Factor Chart for Zone 5
Heating Region House Construction
Loose Average Tight
Appliance operation
TStat Manual TStat Manual TStat Manual
Heat Factor
Region 5 5.55 4.50 4.05 4.50 4.05 4.05

Choose your space heater with your BTU/HR allowance

Space Heaters By BTU/HR
Model BTU/HR
SR6, HB06, HR06 6,000
SR10, SR10T, BF10, HB10, HR10 10,000
HR15 15,000
HR17 17,000
SR18, SR18T, HR18 18,000
BF20, HB20, HR20 20,000
HR25 25,000
SR30, SR30T, BF30, HB30, HR30 30,000

A word of advice:

Make sure to leave proper clearance, as defined by the manufacturer and codes, from all flammable objects such as curtains, drapes, furniture, etc. Also, be sure to be mindful of the safe clearance space when moving furniture around the room.


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