Tips & Advice

How To Choose The Right Size Heat Pump

To get the most out of a heat pump, it's important to choose an efficient model and use it properly. That means having the right size heat pump for the room you want to heat. If it's too small, it may cost you more by working too hard to provide enough heat. If it’s too big, it will emit too much heat, which will go to waste. 

What sizes do heat pumps come in?

Heat pump size doesn’t mean its literal physical bulk (although there are options in that department) but rather it's heating (or cooling) output, which is given in kW, eg. 3.5kW. Heat pumps can range from as low as 1.2kW to 10kW and beyond. The cooler the climate you live in, the more heating capacity or higher kW you’ll need. But that’s just one thing that will affect choosing the right size heat pump; there are many! 

What factors need to be considered?

When choosing the right sized heat pump here’s what you’ll need to keep in mind:

  • Is it mainly for heating or cooling?

  • What’s your local climate like? (eg. it tends to snow at least once every winter, or hot and humid, etc.)

  • What are the average seasonal high and low temperatures?

  • Is your home old and poorly insulated, brand new, well insulated and airtight, or somewhere in between?

  • Do you want to heat single rooms, multiple rooms or an open plan area?

  • How big are the rooms you want to heat?

  • How high are the ceilings?

  • Do you have single or double-glazing?

  • How many people live in your home?

  • Does the room you want to heat get a lot of direct sun?

  • Does your home experience any solar gain?

Calculating size

As you can tell from this extensive list above, calculating the exact requirements for a heat pump is no simple task and must factor in a lot of variables. It’s always best to talk to a heating specialist but if you are wanting to work out a rough idea to help you research the right heat pump, here’s a basic calculation from consumer.org.nz you can try.

Step 1 – Calculate the room’s volume in cubic meters.

Step 2 – Multiply that by 44 watts.

Step 2 - Add 10% to large window areas and a further 10-20% for partial or no insulation.

Step 3 - Multiply this figure by 1.5 for living areas, 1.2 for a bedroom, and 0.8 for other areas.

Example: A partially insulated lounge, 4m x 5m x 2.4m high + 10% for lack of insulation = 53 cubic metres room volume (rounded up). Multiply by 44watts = 2332, now by 1.5 because it’s a lounge = 3498 watts. This means you will need a 3.5kW heat pump.

 Other tips for getting the best performance from your heat pump

  • Check the Energy Rating Label – the more stars, the more energy efficient.

  • Ask the supplier if it performs well at low temperatures (some heat pumps struggle when it dips to almost zero or below outside).

  • Make sure it’s installed in the right location in the room.

  • Get the right type for the space you’re heating (eg. single or multi-split system, high wall or floor mounted, etc.).

  • Clean the filters often and have it professionally serviced at least once a year.

You may even be wondering if a heat pump is even the right solution. Download our free guide to help you decide. If you are keen to learn more about what size heat pump might be right for your home, you’ll get sound advice asking us. Since 1986 we’ve been providing a comprehensive range of climate control solutions, helping families to stay comfortable year-round.

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