Air Source Heat Pump Calculator UK

The air source heat pump market has more than doubled in recent years, with thousands of UK home and business owners opting for this energy-efficient, renewable heating system over a traditional boiler.

If you’re considering investing in an air source heat pump, it’s essential to determine the right size for your needs. A properly sized heat pump ensures optimal performance, energy efficiency, cost savings and comfort in your home or place of work.

Cinergi is an accredited heat pump installer based in Hampshire, serving the south coast. Our aim is to achieve maximum efficiency and cost savings for our customers, so we are meticulous when it comes to heat pump sizing calculations. 

To arrange a detailed consultation and property survey, please get in touch.

air source heat pump calculator

Why does the size of air source heat pumps matter?

When it comes to air-source heat pumps, size matters. It directly impacts the heat pump’s efficiency and effectiveness in heating or cooling your space.

If the heat pump is undersized, it may struggle to meet your heating demands, leaving you in the cold. Conversely, oversized heat pumps will cycle on and off frequently, resulting in energy wastage and potential wear and tear.

So to get the most out of the system, it’s essential to have the right size heat pump installed. Determining what size is appropriate for your property requires detailed calculations based on many different variables. That is why it is wise to enlist the services of an experienced HVAC professional like Cinergi.

What size air source heat pump do I need?

Air source heat pumps are sized in kilowatts. For UK homes and commercial properties, the typical range is 4KW to 12KW.

Larger or more complex buildings may require heat pumps with higher capacities to meet their heating demands effectively. Professional assessment and sizing by qualified HVAC experts is crucial to determine the correct size of a heat pump required.

How to determine the right size air source heat pump for your home or business

To determine the size of the air source heat pump you need, our experienced HVAC engineers take various factors into account, including:

  1. Property type, size and layout
  2. Insulation levels
  3. Heat loss/gain calculations
  4. Regional climate data
  5. Desired indoor temperature
  6. Hot water demand
  7. Type of heating emitter
  8. Coefficient of Performance (COP)

It’s important to note that all these factors are interrelated, and a comprehensive assessment of the property by a qualified HVAC professional is essential to accurately size an air source heat pump.

1. Property type, size and layout

The size and layout of the property, including floor area, ceiling height, number of rooms, and window sizes, are crucial factors in determining the heating or cooling demands of the space. A larger property with more rooms and larger windows may require a higher-capacity ASHP to meet the heating or cooling requirements effectively.

2. Insulation levels

The insulation levels of the property play a significant role in heat retention and energy efficiency. Well-insulated properties with proper roof insulation, wall insulation, and double glazing reduce heat loss and improve the heat pump’s overall performance, potentially allowing for a smaller-capacity unit.

New build properties meet the minimum insulation levels required by building regulations, so they are prime for heat pump installation. However, many older properties have poor insulation levels, and the property may require an insulation upgrade before heat pump installation.

3. Heat loss/gain calculations

Heat loss and gain calculations involve assessing factors such as property orientation, thermal bridging, and air leakage to determine the amount of heat that needs to be supplied or removed from the space. Accurate calculations help size the heat pump appropriately to meet the thermal demands of the property.

4. Regional climate data

Colder regions of the UK may require heat pumps with higher heating capacities to ensure sufficient heating output even during the coldest days.

5. Desired indoor temperature requirements

Personal comfort preferences are considered to ensure the heat pump can maintain the desired temperature levels.

6. Hot water demand

If the air source heat pump is intended for domestic hot water production, the hot water demand of the property is taken into account. This includes factors such as the number of occupants, hot water usage patterns, and required flow rates, ensuring the heat pump can meet the property’s hot water needs.

7. Type of heating emitter

Radiators and underfloor heating systems have different heat distribution characteristics and requirements. Radiators typically operate at higher water temperatures, requiring a heat pump with a larger capacity to meet the heat demand.

The number and type of radiators will have an effect on what size heat pump is suitable, and some homes may require radiator upgrades to maximise the heat pump’s efficiency.

Underfloor heating systems are better suited to air heat pumps, as they utilise a large surface area and heat water at a lower temperature, leading to a smaller heat pump requirement and greater efficiency.


Ask Cinergi for Calculation Advice

Ready to experience the benefits of an air source heat pump for your home or business? Contact Cinergi today to ask for help calculating your requirements.


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Air Source Heat Pump Calculator

Please note due to the complex nature of calculating exactly what size heat pump you need, we recommend contacting us in the first instance. We’ll be able to advise you on your requirements, and be able to provide an accurate quote.

Properties vary, of course, and these figures are intended as a rough guide only. An accurate assessment of what size heat pump is appropriate for your property requires a thorough on-site inspection.

Does air source heat pump size affect running costs?

An undersized air source heat pump may struggle to meet the heating demands of the property, leading to decreased efficiency and potentially higher running costs as it works harder and operates for longer durations.

Conversely, an oversized ASHP may experience frequent cycling, reducing efficiency and causing unnecessary wear and tear. Properly sizing an air source heat pump to match the heating requirements of the property ensures optimal energy efficiency and can help minimise running costs.

What size hot water cylinder do you need?

Unlike combination boilers, heat pumps do not provide hot water “on demand”. Heat pumps work by extracting heat from the air and storing excess heat during low-demand periods. Therefore, you need a hot water cylinder to store the hot water the pump produces. This helps to increase system efficiency and prevent short cycling of the heat pump, which can impact its lifespan.

Generally speaking, the size of the hot water tank required is 15 litres of water per 1 kW of heat pump capacity. Let’s consider an example based on a 4-bedroom property.

Assuming that the property requires an average output of 12 kW from the air source heat pump to meet its heating needs: 12 kW x 15 litres/kW = 180 litres

Contact Cinergi for an air source heat pump quote

With over 40 years of experience in heating homes, Cinergi can determine the best heating solution for your property. Our aim is to make your property more energy efficient and save you money on your energy costs. So we are meticulous when it comes to making our calculations on the right size of heat pump for each property.

As well as specialising in air and ground source heat pump installation, we are experts in traditional gas, oil and LPG boilers. This enables us to offer a wide range of heating solutions tailored to your specific needs and budget. Whether you require a heat pump, a replacement boiler, or a hybrid of the two, our independent advice will ensure you can make an informed decision.

Ready to experience the benefits of an air source heat pump for your home or business? Contact Cinergi today to schedule a consultation.