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How to Find the Correct BTU size for a Ductless Heat Pump that is right for My House Size?

Wednesday, August 20, 2014

Heat pumps provide an extremely effective source of heating and cooling and, due to the efficiency of the refrigeration cycle, would typically generate three to four times more heat energy than is used by its compressor. Heat pumps are efficient and more economical than gas fired furnaces.

Ductless heat pumps are usually split with an indoor unit containing an air circulating fan and a heating coil connected to an external system unit housing the compressor. As with any heating and cooling equipment, correct BTU sizing is important for comfort because a unit that is either too small or too big will not operate properly.

Available Systems

Ductless heat pumps are supplied in various configurations. The simplest is a single zone heat pump that has an outdoor unit connected to an indoor air handler, which is discreetly mounted on the wall. An alternative is a multi-zone heat pump that has a large outdoor unit connected to several internal units. Individual temperature control of each indoor unit is possible, providing flexible control of heating and reducing energy usage.

Heat Pump BTU Sizing

It is important to size the ductless heat pump correctly. If it's too small it will run continuously and not provide sufficient heat, leading to discomfort and potential failure of the heat pump compressor. If it is too large, the compressor will cycle frequently and room temperatures will fluctuate with poor humidity control.

Although it is recommended that sizing of multi-zone systems is done professionally by a qualified contractor, there are simple guidelines to estimate the required unit size. The method is as follows:

  • Calculate the floor area of the room to be heated by multiplying its length by its width.
  • If the area is calculated in square feet, multiply the area obtained by 20. If metric units are used, multiply the area by 200.
  • The answer is the approximate BTU required.
  • Repeat this calculation for each room.
  • If using a multi-zone ductless heat pump, add up the BTU calculated for each room to give the total BTU required.
  • When selecting a heat pump choose one that is slightly larger than your calculated value.

If you have any doubts, get professional advice before deciding on the size of the heat pump.

Benefits of a Ductless Heat Pump

Ductless heat pumps provide several benefits that improve comfort and reduce utility bills:

  • Energy Usage: Your heat pump costs less to run than a gas furnace. An Energy Star® rated heat pump works down to minus 30°C; thereafter, use your gas fired furnace. Judicious use of your heat pump means you will save money.
  • Summer Cooling: The heat pump operates as an air conditioner so you have the dual benefit of heating and cooling.
  • Selective Heating: The temperature in each room with an air handling unit can be individually controlled.

Designed for Canada

At one stage it was believed that Canada was too cold for heat pumps, but the introduction of high energy-efficient units has changed this and their installation is supported and encouraged by the Department of Natural Resources Canada.

Ductless heat pumps save energy, heat and cool your home, and although not a DIY job are easy to install while requiring minimal interference to the home. Establishing the correct BTU for your home size is relatively straightforward, although it is important to be aware of how well your home is insulated, one of the reasons why having it sized professionally may be wise. Heat pumps complement your central heating system and can be used in conjunction with your furnace.


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