What Size Heat Pump Do I Need?

Installing a heat pump is a huge expense. Before upgrading your central heating system, it’s important to ensure you investigate heat pump sizing and choose the right unit. If not, you’ll be stuck with a heat pump that’s not sufficient to supply your property with hot water and heating. 

Below we’ll include everything you need to know including:

• A quick summary of this air source heat pump sizing page
• Details of our heat pump sizing calculator
• How to calculate what size heat pump you need
• The importance of choosing the right size heat pump
• How big are heat pumps? 

In Summary: What Size Air Source Heat Pump Do I Need?

Don’t have time to read this guide in full? Bookmark it for later and read this quick-fire summary instead…

For residential properties, popular heat pumps come in sizes ranging from 5kW-16kW. Commercial properties tend to use much larger units. 

This isn’t a one size fits all approach. Whilst one 3-bedroom house might see a 7kW unit suffice, another might need a 10kW unit or more. The size of your property, quality of insulation and hot water / heating demand (among other things), all contribute to determining which kW output heat pump is the most suitable for your property.

Most importantly, buying a heat pump that’s too big or small is going to have some repercussions. 

Buy one that’s too big? You’re spending a lot more cash than you need to. Not to mention the fact that the motor constantly cycling on and off isn’t good for its long-term health.

Buy a heat pump that’s too small? The unit will be overworked and wear out well before it’s time. Plus, it’s not going to be able to keep up with hot water and heating demand in your property; showers will be luke-warm and radiators won’t get up to temperature.

And finally, to have a heat pump installed, you’ll need a suitable installation area (usually outside). A Vaillant aroTHERM Plus 7kW for instance, is 110cm x 97cm x 45cm.

The easiest way to check what size heat pump you need? Use our heat pump calculator here. 

Click a few options and we’ll suggest the most suitable unit on-screen, including a fixed price for installation. Our calculator will also let you know if you’re eligible for the Boiler Upgrade Scheme, which could save you £7,500 thanks to government grants!

Heat Pump Size Calculator

You’re probably already realising that calculating heat pump sizing isn’t particularly easy. We fit air source heat pumps from 5kW right through to 16kW (for residential properties, bigger for commercial). 

Put simply, there are dozens of variables that affect the size (in kW) heat pump you need for your property. These include the likes of: 

• Type and quality of insulation
• Size and amount of radiators
• Square footage of your property
• The average temperature you keep your central heating at
• How many bathrooms and separate showers are in your property
• The list goes on…!

That’s why we’ve created a quick and easy to use air source heat pump size calculator. Our heat pump sizing calculator takes into account all the important details that determine the size heat pump you need, and will give you a fixed price on-screen for the most suitable air source heat pump.

As an example, using the heat pump sizing calculator we got this fixed price on-screen within 2-minutes for a Vaillant 7kW unit. We used a 3-bedroom house in this example.

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And whilst the price of £10,000+ is certainly more than an average combi boiler replacement, you can see this qualifies for a government grant. This comes in the form of the Boiler Upgrade Scheme, meaning it would actually cost less than £3,000!

Try it for yourself by jumping over to our heat pump sizing calculator here. 

Calculating Air Source Heat Pump Sizing

As we’ve mentioned above there are dozens of variables that affect the size of the heat pump you need for your property, from the amount of radiators to exactly how big your property is. 

Below we’ve created a table with estimates of what size heat pump you’ll need based on the number of bedrooms your property has, as well as the size of your house (m²).

Please bear in mind these are very rough estimates. Dozens of variables mean that no heat pump installation is the same. For instance, one 3-bedroom house might need a 7kW heat pump, whereas another might need a 10kW or bigger. 

The only way to get an accurate representation of exactly what size heat pump you need is by using our heat pump sizing calculator here. This clickable pump sizing calculator will suggest the most suitable heat pump size from a leading brand with a long warranty.

And if you want to understand how prices vary from property to property, check out our guide to heat pump installation costs here. 

The Importance of Correct Heat Pump Sizing

When sizing an air source heat pump, you always want to go slightly bigger (but not too big). 

By buying a unit that can easily deal with demand for heat and hot water in your property, the pump won’t be overworked. It also means in exceptionally cold winter months, there’s a little bit of wiggle room so that your unit can keep up with the heat and hot water demand in your property.

That said, sizing a heat pump that’s much too large will mean that: 

• The motor runs on short cycles constantly, which isn’t good for the pump’s components and could lead to costly repair bills
• Upfront cost will be far greater than it needs to be, thousands of extra expenditure on a heat pump that’s too big will reduce the overall cost savings you make over the next decade or so
• You’ll need additional space to install it, heat pumps (even smaller 5kW to 7kW units) are large…and fitting a pump that’s 10kW or bigger when you don’t need to, is extra space you’ll need

On the flip side, fitting an air source heat pump that’s too small is going to cause even more problems including:

• The pump will be constantly overworked to keep up with hot water and heating demand, meaning it will wear out years before it should; a costly replacement will be needed
• An undersized pump will have to work at maximum capacity and will drastically increase your electricity bills; a larger heat pump that isn’t overworked will be much more energy efficient
• If the pump is far too small for your property, you’ll find your heating doesn’t ever get up to temperature and water from showers is luke-warm
  
  

Heat pump sizing can be confusing. If you’re still not sure what size heat pump you need, use our air source heat pump calculator here. It’s a clickable form that takes less than 2-minutes to complete.

How Big Is An Air Source Heat Pump?

Now you understand what size heat pump you need, another thing worth considering is how big they are. 

A heat pump will be fitted outside, so if you have plenty of space in a garden or beside your property, this isn’t going to be an issue. But for those with compact gardens (or none at all, such as a small flat), this isn’t the best heating solution for your home.

Typically, a heat pump is going to stand 1m-1.5m high, and the width is likely to be in the region of 0.5m-1m; they’re similar in size to other household appliances such as a dishwasher. 

Using the Vaillant aroTHERM Plus 7kW we mentioned above, the dimensions for that unit are 110cm x 97cm x 45cm.

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