A heat pump is a brilliant way to reduce your carbon footprint and increase your home’s energy efficiency. Not only are heat pumps low maintenance and have a long service life, but they are also a sustainable and emission free way of heating and providing hot water to your home.
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Heat pump sizing: What size heat pump do I need?
Understand how to select the right size heat pump for your property’s needs.
How big is a heat pump?
When asking, ‘What size heat pump do I need?’ you are referring to its power output, measured in kilowatts (kW). This indicates how much energy the heat pump can generate for your home.
The size of the heat pump directly impacts its initial cost to purchase and install. Higher power output means a higher cost for both the appliance and its installation.
If you're wondering about the physical size of a heat pump, you’re asking about its dimensions. Heat pumps, particularly air source heat pumps, are generally compact units, about the size of two domestic wheelie bins, so they won’t take up too much space.
However, you still need to ensure you have enough room for correct installation and airflow.
The size of a heat pump can vary by manufacturer. Below is a breakdown of Vaillant heat pump sizing:
Height (mm) | Width (mm) | Depth (mm) | |
|---|---|---|---|
| aroTHERM plus 3.5kW | 765 | 1,100 | 490 |
| aroTHERM plus 5kW | |||
| aroTHERM plus 7kW | 965 | ||
| aroTHERM plus 10kW | 1,565 | ||
| aroTHERM plus 12kW |
Height (mm) | Width (mm) | Depth (mm) | |
|---|---|---|---|
| aroTHERM plus split 3.5kW | 765 | 1,100 | 490 |
| aroTHERM plus split 5kW | |||
| aroTHERM plus split 7kW | 965 | ||
| aroTHERM plus split 10W | 1,565 | ||
| aroTHERM plus split 12kW |
Height (mm) | Width (mm) | Depth (mm) | |
|---|---|---|---|
| aroTHERM 5kW | 840 | 980 | 408 |
| aroTHERM 8kW | 975 | 1,103 | 463 |
| aroTHERM 11kW | |||
| aroTHERM 15kW | 1,380 |
Height (mm) | Width (mm) | Depth (mm) | |
|---|---|---|---|
| flexoTHERM 5kW | 1,256 | 1,192 | 785 |
| flexoTHERM 8kW | |||
| flexoTHERM 11kW | |||
| flexoTHERM 15kW | |||
| flexoTHERM 19kW |
Understanding heat pump sizing
Heat pumps are rated based on their heating and cooling capacities, typically measured in British Thermal Units per hour or tonnes. One tonne is equivalent to 12,000 BTUs per hour. The size of the heat pump you need depends on various factors, including the size of your home, the local climate, insulation levels, and the number of windows and doors.
Your installer will be able to advise on the best heat pump for your property, but factors influencing the size of your heat pump may include:
-
Home size and layout
The larger your home, the more BTUs you will need to maintain a comfortable temperature. Apartment buildings or multi-story homes may require additional consideration, as heat distribution can vary between floors.
-
Climate
The local climate plays a significant role in determining the size of your heat pump. All Vaillant heat pumps have been tested in a variety of climates and can operate in temperatures down to -25°C. Vaillant heat pumps also have salt corrosion protection to aid longevity if your property or heat pump is near the shore.
-
Insulation
The correct level of insulation will reduce the load on your heat pump by maintaining the desired temperature more efficiently. Homes with poor insulation will require a larger heat pump to compensate for the heat loss or gain. Cavity wall insulation, double or triple glazing, and loft insulation are all types of insulation that will improve the ErP rating of your property.
Different types of insulation -
Occupancy and usage
The number of people in your home and their typical activities can also influence the size of heat pump you need. You should consider how many bathrooms your property has so that your heat pump can meet your heating and hot water needs.
How to calculate the heat pump size that you need
For accurate heat pump sizing, get in touch with one of our Vaillant installers. They can perform a detailed heat loss calculation and recommend the best heat pump size for your home. They can also help with selecting the correct Vaillant heat pump, control and cylinder to help meet your heating and hot water requirements.
Find out more about how to buy a Vaillant heat pump.
Space needed for a heat pump
External space needed for an air source heat pump
Air source heat pumps are usually installed on the exterior of properties. You may be able to install the heat pump against an exterior wall, but you will need to leave a small gap.
When installing a heat pump outside your property you will need:
- A flat solid surface to mount your heat pump.
- Enough space to account for the width and height of your chosen heat pump.
- At least 1.5 metres of clear space in front of the heat pump fans to maintain proper air flow and avoid recirculation of cold air.
- Space for pipes to deliver heat into your property, the size of which will vary. This needs to be close to your property to feed pipes and electric cables.
Be aware that certain heat pumps, like the aroTHERM plus air source heat pump, use an R290 natural refrigerant which needs certain clearances.
Internal space needed for an air source heat pump
You will need interior space for:
- A hot water cylinder, like uniSTOR, which is compatible with Vaillant heat pumps (126.5cm H x 59.5cm W). If you are upgrading to a heat pump from a system or regular boiler, you will already have space for a cylinder.
- A heat exchanger unit which is roughly the size of a regular gas boiler (e.g. aroTHERM heat exchanger 50cm H x 36cm W)
- A heating control like the sensoCOMFORT (10.9 cm H x 17.5cm W)
- The myVAILLANT connect internet gateway (9.6 cm H x 12.2cm W) to allow full system control via the myVAILLANT app.
Save money on heat pumps
If you are installing a heat pump and are based in the UK, be sure to find out if you are eligible for a UK heat pump grant.
As of 2024, there are a range of grants available, including:
SUMMARY
Properly sizing your heat pump is key for comfort, energy efficiency, and system longevity.
Consider factors like property size, climate, insulation, and usage to determine the right size for your needs. Consulting a professional ensures you get the best advice and most suitable heat pump. Whether installing a new heat pump or replacing an old one, taking these steps will help you achieve the best results.