Air source heat pumps: a guide to getting the right size
What’s the best heat pump size for your home?
Heat pumps are the eco-friendly way to heat your home, and they’ll save you money in the long run. But for you to get the most out of them, choosing the right size is really important. Get a heat pump that’s too small and it might struggle to keep your home as warm as you’d like. Go too big and it’ll use lots of unnecessary electricity.
Read on to learn what size you need to heat your home efficiently and drive energy costs down.
Get an air source heat pump with Hive
What are the benefits of choosing the right heat pump size?
A heat pump that’s the right size will use less energy without needing to strain and it will cut your heating costs over time. Plus, your home will be more comfortable to live in because it’ll maintain a more consistent temperature. With your heat pump working in harmony with your home it will strain less and last longer.
What determines air source heat pump size?
It stands to reason: bigger homes with large open floor plans need big heat pumps, while small heat pumps are better for smaller homes. But there are a few other factors that play a part too.
How’s the insulation in your home? If it retains heat well, you may only need a small heat pump. And then there’s climate. If you live in Scotland, winters are colder, while on the coast, you’re more exposed to high winds. In both cases the colder temperatures outside mean you’ll likely need a bigger heat pump to compensate.
You also need to factor in air leakage, number of windows and how energy efficient those windows are.
What are the standard air source heat pump sizes – and what size house can they heat?
Air source heat pumps are available in many different sizes. The most common are usually from 3.5kW – 16kW. The correct size will depend on the results of a heat loss survey of your property.
Here’s a simple breakdown:
- Smaller units around 3.5kW are ideal for 1-to-2-bedroom homes or small apartments.
- Medium-sized units between 4kW and 8kW are great for an average two-to-three-bedroom house. Possibly even a four-bedroom house if it’s well insulated.
- If your home is four-bedrooms or above, the chances are you’re looking at a larger heat pump. They range between 10kW and 16 kW. But this could be lower depending on the level of insulation in your home.
- During a heat pump survey, your surveyor will work out what size is right for your home. And give you a personalized estimate of how much it would cost to run.
Small air source heat pumps
If you live in a one-bedroom house or small apartment, a small air source heat pump will work best. They can comfortably heat 500 to 600 square feet, plus they’re quiet and don’t take up lots of room so you won’t bother your neighbours.
A heat pump that’s too small for your home will give you a lot of headaches! It will try to compensate by running more often which will ramp up your energy costs and make breakdowns more likely.
Medium to large air source heat pumps
Medium-sized heat pumps are ideal for homes between 1,000 and 2,000 square feet, while large heat pumps are better for homes over 2,500 square feet. Their larger capacity makes it easier for them to generate enough heat, even when temperatures drop.
Size of home | Estimated annual energy demand | Estimated required heat pump size |
1-2 bedroom | 7,500 kWh | 4W |
2-3 bedrooms | 11,500 kWh | 6-8W |
4 bedrooms | 17,00 kWh | 10-12W |
How to calculate the right size air source heat pump for your home?
To figure out what size air source heat pump is right for you, you need to work out your home’s ‘heat load’. This is the amount of heating it needs to maintain a comfortable temperature. Heat load is usually measured in British Thermal Units (BTUs) or kilowatts (kW). It’ll come as no surprise that a larger heat load needs a larger heat pump!
You can work this out yourself. Equally, any heat pump supplier can do it for you. For instance, if you go with a Hive heat pump, we can arrange a free home visit with one of our trusted installers to work it all out. Here’s what they’ll do:
1. Measure your home: First up, they’ll measure the total heated area of your home.
2. Check insulation: They’ll check how well insulated your walls, floors, attics, windows and doors are.
3. Consider the climate: If you live in a particularly cold or windy part of the country, they’ll factor this in.
4. Calculate your heat load: With all this info – as well as taking any air leakage into account – they’ll be able to accurately calculate your heat load.
Frequently asked questions
How does efficiency and size relate to air source heat pumps?
If your air source heat pump is too big it will switch on and off more often than is needed. This is called short cycling and it’s not great for your pump – it makes it less efficient, causes wear and tear, and means it won’t last as long. On the other hand, if your heat pump is too small it will struggle to keep your house warm. It will try (and fail!) to get the temperature up by running continuously which will waste energy and wear it out.
When should you choose a small air source heat pump?
If you live in a flat, small house or well-insulated home that doesn’t need lots of heat to stay warm, a small pump will do the job. They also work really well as secondary heating for specific rooms, so if you have a home office, extension or guest room it might be worth getting one.
How does the size of an air source heat pump affect its price?
Larger units have higher upfront costs because they have bigger heating capacities and more advanced components. Running costs vary with size too. Large heat pumps use more energy but can be efficient if sized correctly for a larger home, while small heat pumps are more economical for compact spaces.
Basically, if you get the right sized heat pump it will be more energy efficient but if it’s oversized or undersized that’s when inefficiencies creep in and energy bills creep up.
The good news is that the government wants to get you using the best sized heat pump for your home, so they’ve introduced grants like the Boiler Upgrade Scheme (BUS) to help cover costs.
Getting professional advice on heat pump sizing
It takes more than just knowing your home’s square footage to get the right size heat pump, so we’d always recommend using a professional. They’ll have the tools and expertise to accurately assess your home so they can calculate its heat load.
When you buy a heat pump with Hive, you can arrange a free home survey with one of our trusted installation partners, along with a personalised quote tailored to your home.