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Too Big, Too Small, Just Right; Goldilocks & Heat Pump Sizing

There’s a lot of factors that contribute to deciding if a heat pump is right for your home. From what source of heating you current use, and how much you are spending and what you stand to save, to the upfront cost of a heat pump and the available rebates and financing.

But if after all of this you decide that you are going to take the dive into heat pump you are still left with the question of what size heat pump is right for you? Let’s take a look at the factors at play in this decision and why a bigger heat pump is not always better.

How Is Your Home Laid Out?​​​​

The floorplan of your home has a considerable impact on the size of heat pump you will require.

For example, if your main goal was to add air conditioning to a master bedroom of around 300 square feet, then a 9,000 BTU mini-split heat pump would be more than adequate.

Whereas a space that is closer to 700 square feet, such as an open concept living room, kitchen area may require a 12,000 to 15,000 BTU heat pump.

What are BTU’s? 

BTU (British Thermal Unit) is a measurement of the amount of energy in the form of heat that is required to raise the temperature of one pound of water by one degree Fahrenheit.

When used in relation to heating and cooling devices the measurement is actually BTU per hour, though is frequently shortened to BTU.

Here’s a quick reference guide to estimate BTU per sq/ft for sizing

9,000​​​​​ BTUs

300 - 450 sq.ft

12,000 BT​​​​​Us

500 - 600 sq.ft

15,000 BTUs

600 - 850 sq.ft

18,000 BTUs

1,000 sq.ft +

Additional Considerations For Sizing

If your home has lots of windows, they will generate heat and this can be used to your advantage. This is what is referred to as solar gain, and it can lower the size of heat pump required.

Similarly, if your home is well insulated you may be able to use a smaller machine, as there will be very little heat loss. Conversely, if your home has higher heat loss through old windows and doors or poor insulation then you might require a larger heat pump to compensate. These factors will all be taken into account when your heat pump is installed by a certified professional.

Bigger Doesn't Mean Better

It’s an easy assumption to make that a larger heat pump will be more efficient and provide better heating and cooling capabilities. This is often far from the truth.

Heat pumps are most effective when they can maintain a temperature for an extended period. They draw the most power when they first turn on and are heating or cooling a room to temperature. They are at their most energy efficient once the desired temperature is approached and they can slow down enter a “cruise control” mode.

If a heat pump is too large for the space it's in, then it will achieve temperature too quickly and will shut off without entering the power saving cycle. This lead to the heat pump only entering the high power consuming startup cycle.

It can also lead to another unforeseen, and potentially very damaging issue.

During the winter your heat pump has to run for at least 15 minutes to enter a “defrost cycle”. This keeps ice from building up on the outdoor unit by melting it off. If your heat pump is constantly stopping and starting, it may never get the chance to defrost allow ice to form on the unit. At best this will restrict airflow, at worst it could burn out the motor if the vent is completely blocked. It could even lead to broken fan blades if the ice gets inside the unit. 

A properly sized heat pump is the only way to get the full power saving benefits that should come with a heat pump. To ensure that you are able to receive these benefits make sure to have your home assessed by a professional who can help you select the proper size unit for the area.   

  • Heat pumps too big, or too small don't operate efficiently 
  • A properly sized heat pump maximises savings 

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