Do you need to Calculate the Heater Size for your House?


  1. find your house and zoom to it
  2. click on the corners of your house in the map, so the your home area is covered
  3. select your insulation type
  4. the area and heater load will be displayed
  5. click on the Clear Points button to start again

    Now compare the heater load (kilowatts or BTUs) to your potential heater specifications.

    The Heater Size Calculator

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    House Type:

    Your central heating system is about to pack it in (or already has).  You desperately need a new one.  Preferably before you freeze solid this winter.

    But figuring out what which furnace you need is frustrating.  There's a heap of boilers for houses available, spec'd at different capacities (and prices), but how do you figure out which home heater is right for your house heating?

    A good starting point in selecting a home air heating unit is to figure out the heat load your central heater needs to provide to maintain a comfortable temperature in your house on a cold day in winter.

    To figure out the required heat load of a furnace, you need to take a step back and measure the area/volume that it has to heat.  That means measuring your house size.

    So if you figure out the home area that needs to be heated, and calculate the boiler energy needed, then you can narrow down your list of heaters to those that have the heating energy capacity to heat your home.

    You can use the heater size calculator above to mark out your house on the map, and it will give you a rough indication of the:
    • area in meters squared
    • area in feet squared
    • area in squares
    • heat load in kiloWatts
    • heat load in BTUs (British Thermal Units)
    If you can find the Furnace specifications for the heater your interested it, it will list the kiloWatts or BTU's that the heater is capable of producing.

    You can use the heat load from the heater size calculator map above (in either kilowatts or BTUs), to determine if the boiler you're interested in can do the job of heating your home.

    Information and Disclaimers

    Calculations for the basis of the heater size calculator heat load are based on guidelines in Choosing a Heating System, a document published by the Sustainable Energy Authority VictoriaChoosing a Heating System is recommended reading, and along with other relevant energy advice documents can be found here:

    Heaters should be sized to maintain a comfortable temperature in a room on an average cold day in winter. This "heat load" is determined by room dimensions, insulation levels, window areas and coverings, indoor and outdoor temperatures, etc.

    The Heater Size Calculator gives a very rough (possibly inaccurate) indication of heat load for an area, and does not cater for all possible factors in determining the heat load.

    The Heater Size Calculator assumes a 2.4 meter ceiling height. It does not apply to off-peak electric storage heaters

    The size of your system should always be determined by your supplier. This is especially important when sizing central heating systems.