Certain calculations need to be completed before the installation of an Air Source Heat Pump (ASHP) to help it function efficiently.
These calculations are mainly based on the size of the heat pump and household type.
An appropriate size of heat pump
Bigger is not better when it comes to installing an air source heat pump. All properties vary in terms of size and location; therefore, different types of heat pumps are manufactured to meet their individual needs.
As a rule of thumb, the heat pump’s power is directly linked to the demand for heating needs in a household.
For example, you will not require an industrial boiler to heat your two-bedroom flat. The same is the case with an air source heat pump size.
Technically speaking, ASHP has a kW rating, representing their output. Most heat pumps range from 4Kw to 15 kW.
Now you will not be installing a 15-kW heat pump to a property whose heating needs are only 5kW. It will only result in frequent switching off and ultimately high energy bills.
Similarly, a heat pump with too low an energy rating won’t be efficient enough to heat your home and will increase your bills too.
How to calculate the right size air heat pump
To avail the maximum benefit from the air source heat pump, it must be correctly sized for your home and your home must be well insulated.
Failure to choose the right size of heat pump could result in wasted energy, increased electricity bills and unnecessary heat loss.
A Microgeneration Certification Scheme (MCS) accredited heat pump installer will be able to recommend the ideal air source heat pump size for you.
Since the newly built-in UK have a higher standard of insulations, it is ideal and straightforward to install air source heat pumps.
However, you will need a detailed survey for the older building to check their quality of insulation and amount of heat loss.
As a rough guide, you can check the recommended air source heat pump (ASHP) sizes based on your house size and standard of insulation below:
| Household type | Recommended ASHP output |
| 2-bed house/flat | 5 kW |
| 3-bed house with poor insulation | 9 kW |
| 4-bed house with good insulation | 9 kW |
| 4-bed house with poor insulation | 16 kW |
| 5-bed house with good insulation | 16 kW |
How to Find an Ideal ASHP for your home?
The above table just gives you a random idea about the correlation between the size of your property and recommended ASHP output.
In the real world, however, a certified installer takes different factors into account while working out an ideal size of your ASHP. These factors are:
- Size of your property.
- Standard of insulation (good or poor?).
- Numbers of radiators and underfloor heating.
- Location of your house.
- ASHP size and running cost.
- Size of hot water cylinder you need.
Size of your property:
Not all three-bedroom houses are the same. The area of the house is not defined by the number of bedrooms it has but by its covered area.
For example, the rooms in a terraced house would not be as big as in a detached bungalow. So, a three-bedroom detached bungalow will have more heating needs than a three-bedroom terraced house.
Similarly, the number of bathrooms or a kind of lounge a property has makes an important point to consider while working out for an ideal ASHP.
Generally, a heat pump with an output between 4KW and 12 KWs is suitable for most homes.
Standard of insulation
The standard of the insulation in your home links with the kind of ASHP it can have and its efficiency.
A house with poor insulation would not be benefitted from the heat pump as a house with very good insulation.
This is the reason it is much more efficient and straightforward to install an ASHP in new homes since they maintain a very high level of insulation. A heat pump with a lower energy output can perform significantly good in new homes.
On the contrary, old homes must meet the minimum insulation levels required by building regulations. This means that you may need to first improve the insulation of your home before going to install ASHP.
Numbers of radiators and underfloor heating
ASHP requires a larger surface area to keep your home warm because it consistently heats water at a lower temperature than a traditional boiler. A home with underfloor heating can use air heat pumps with lower outputs.
However, you can still install ASHP if you do not have underfloor heating or plenty of radiators.
You just require adding more radiators or upgrading the existing ones to larger designs. This will help to increase the surface area which allows them to reach higher temperatures.
Location of your house
ASHP works more efficiently in a warmer climate because it extracts heat from the air outside.
So, if you are living in an area with warm temperatures most of the year, you do not have to worry about the performance of your ASHP.
On the contrary, an air pump must work harder if you are living in a colder region. In that case, you will need ASHP of higher output, but you do not have to worry about their efficiency. The air heat pumps can perform at a temperature as low as -25C.
But your installer still needs to see the average below the temperature of the area you live in to make the right decision about the input your ASHP requires for better performance.
ASPH size and running cost
A wrong air heat pump size could be very costly. As said above a higher energy rating heat pump for your smaller property will only result in frequent switching off and ultimately high energy bills.
Similarly, a heat pump with too low an energy rating won’t be efficient enough to heat your home and will increase your bills too.
This means that an appropriate size air heat pump should be installed for a greener and more cost-efficient source of heating.
Size of hot water cylinder you need
The right size hot water cylinder is essential to meet your home’s demand efficiently. typically, a 4-person household will need a hot water cylinder that can provide around 200 litres daily.
Having that said you won’t necessarily need a 200-litre capacity hot water cylinder, as some heating systems may partially reheat water throughout the day.
A certified installer after considering different factors will recommend an ideal hot water cylinder size for you that is able to meet the hot water demand of your household.
Air source heat pump calculator conclusion
While ASHP is a sustainable and greener option to meet your heating needs, it should not cost you a fortune.
It is important to take into consideration of different factors when getting ASHP installed which helps to keep its running cost down.
An MCS accredited installer will help you choose the right size of the heating pump while reviewing the size of your home, insulation, heating system and location.
Ends