What Size Heat Pump Do I Need? Your Complete Guide to Heat Pump Sizes

Though not the only factor, the size of your heat pump, measured in kW (kilowatts), is directly proportional to the amount of heat your heating system can generate. Whether it is underfloor heating, water heating, or air-to-air heating, if you want to achieve the desired temperature, you need to select the right heat pump size.

In this blog post, we'll go over everything that goes into choosing the right air source heat pump size for homeowners. If you've always wondered how to achieve ideal indoor temperatures, continue reading!

Does the Size of the Heat Pump Matter?

It is hard to overstate the importance of the heat pump size. It dictates various important aspects of your heating system and its performance:

• Amount of heating the system generates: The heat pump makes the heating system function by leveraging differences between outdoor and indoor temperatures. The size of the heat pump, measured in the energy it handles and not in physical size, is directly proportional to the amount of heating or cooling it can produce. Whether it is a hot water cylinder or underfloor heating, this principle remains constant across all types of heat pumps.
• Amount of energy the system consumes: Naturally, the bigger the size of the heat pump installed, the more energy the system consumes. This isn't bad, necessarily. If you have a bigger or poorly insulated house, you need a higher amount of energy if you want to reach the desired room temperature. This is something you should keep in mind when choosing the size of the heat pump.
• The time it takes to reach desired temperatures: The size of heat pump also impacts the power output it is able to handle. Larger heat pumps have a higher power and heating output, which generally impacts the time it takes to reach an ideal temperature.

Factors That Go Into Choosing the Right Heat Pump Size

Choosing the right size heat pump isn't an easy task, and many factors go into the decision. Understanding these factors and why they matter is important to make an informed decision when buying a heat pump. In this section, we'll go over all of them in great detail!

#1 The Size of Your Home

The biggest and most obvious factor when choosing a heat pump is the size of the home. The bigger your home the more energy it needs to properly heat up, and only larger heat pumps will have the necessary energy output to do the job properly.

There are no hard and fast rules, here, sadly. Heat pump sizes range from 5 kW to over 17 kW. Generally, one or two-bedroom apartments built on an area of 100 square meters of less can be sufficiently heated by a 5kW heat pump. A home that occupies 200 square meters is double the size and likely need double the heating, which means a 10 kW heat pump should do the job properly.

The size of the home isn't the only factor in choosing the heat pump, however, and the above should be looked at more as suggestions as hard-and-fast rules you can strictly apply.

#2 The Type and Efficiency of Your Heating System

There are different types of heat pumps and heating systems - their efficiency and by extension the size of heat pumps they need inevitably vary. When choosing a heat pump, you should take this into account!

The most common types are geothermal, water-source, and air-source heat pumps. Geothermal heat pumps use the ground as a source for heating, water-source heat pumps use nearby water bodies, which generally store heat, and an air-source heat pump extracts heating from the outdoor air to heat indoors.

The purpose of the heating system also impacts its efficacy. Is it only used to provide hot water? Is it used to provide underfloor heating? Is it used to directly change the air temperature? Whether you are using a ground source heat pump or an air source heat pump, heat loss is different across different applications, which impacts the heat pump size you should use!

#3 Heat Loss and Temperature Flow in Your Home

Homes come in different sizes and shapes, and this naturally impacts air flow, temperature flow, and ultimately, heat loss. Add to that the difference in insulation between different houses, and the picture becomes even more complicated. 

A house that has excellent insulation and proper airflow might be able to get by with just a small heat pump. Meanwhile, if the insulation isn't up to par and the house's structure doesn't particularly lend itself to central heating, you'll need a larger heat pump to get to the desired room temperature. 

Here, what's important is calculating heat loss in your home and then choosing the heat pump you need based on that information! 

#4 Local Climate

The bigger the difference between the initial air temperature and the desired air temperature, the larger the amount of energy you need to achieve this. This isn't particularly surprising, but many homeowners simply buy heat pumps based on the size of their house and don't take into account the local temperature. 

If you are living in a relatively temperate area in Southern England where the coldest temperature ever hardly goes below zero, then the size of heat pump you need will probably fall on the smaller side. Otherwise, if you live in far Northern regions of the country and regularly suffer from lower room temperatures, you need larger air source heat pumps to get the job done! 

Conclusion

Choosing the right heat pump size is essential when designing your heating system. Sadly, the process is complex, and there are a variety of factors that should inform your decision: These include the size of your house, the local climate, the insulation, and the efficacy of the heating system! 

Calculating heat loss or coming up with a boiler upgrade scheme that adheres to building regulations can be complicated. This is why here at Culm Stores, we help you find the heat pump you need based on your requirements, climate, heating system, and more! Get in touch now and let's take care of the rest!

Heat Pump Size FAQ

How Do I Calculate What Size Heat Pump Do I Need?

Calculating the heat pump size you need isn't an exact science, but there are a few questions you can ask yourself to get an approximate idea! 

• What's the size of your home? 
• Do you need an air-source heat pump or a ground-source heat pump?
• How insulated is your home and how cold is the local climate? 

What Size Air Source Heat Pump Do I Need for a 4-bedroom House? Does the Heat Pump Size Matter? 

The size of the heat pump is influenced more by the size of the house than the number of rooms it has, but approximately, a 4-bedroom apartment usually occupies 200 square meters, which means a heat pump of about 10 kW should be enough to achieve the desired room temperature!

Is it better to oversize or undersize a heat pump?

Generally, it's better to slightly oversize a heat pump than to undersize it. A small amount of oversizing (up to about 15%) can provide:

• Better performance on extremely cold days
• Faster heating of spaces
• Longer equipment lifespan due to reduced strain

However, significant oversizing can lead to:

• Higher initial costs
• More frequent on/off cycling, which reduces efficiency
• Humidity control issues in cooling mode

The best approach is to size the heat pump as close to the building's needs as possible, with a small margin of extra capacity.

What size room will a 6kW heat pump heat?

A 6kW heat pump can typically heat a room of about 50-60 m² (540-645 sq ft) under average conditions. However, the exact area depends on several factors, including:

• Building insulation
• Ceiling height
• Number and size of windows
• Local climate
• Desired indoor temperature

In a well-insulated home, a 6kW heat pump might heat an even larger area, while in an older, poorly insulated building, it might be insufficient for the same area. It's always recommended to have professional heat load calculations done to accurately determine the required heat pump capacity for a specific room or building.