Can air source heat pumps work with radiators?

Air source heat pumps (ASHP) are becoming more popular as people look for ways to become more sustainable. Lower their energy bills. Whilst at the same time playing their part in helping the environment.

However, there is one common question when switching from a typical heating system. For example, a gas heating system to an air source heat pump. Do they work with radiators? 

There are three main factors. Apart from the flow temperature. That will determine what size radiators you need to compliment your ASHP and help it to run at its maximum efficiency. 

What is an air source heat pump?

Simply put it is a way of extracting the heat from the air outside and bringing into your home to provide you with heating and hot water. An external unit is placed outside and the air is drawn in as a liquid. This is then turned to a gas and a compressor further heats this. It is then distributed to your heating and hot water circuits within your home.

There is an internal unit, typically smaller than a standard boiler, which is connected to the external unit. 

You may wonder what happens in winter when the temperature regularly drops to below freezing.

Air source heat pumps are designed to be able to provide you with a warm home and hot water with temperatures up to minus fifteen degrees. It may require more electricity to do this, but your heat output will not be affected no matter what the weather is like. 

There are two types of systems available.

Air to Air systems and Air to Water systems. 

Air to air

Will provide you with space heat but not hot water. The system requires a warm air circulation unit to distribute the heat around your home. 

Air to water

This is the most common type of system used within the UK and will provide you with both space heat and hot water. It is distributed around your home via your wet central heating. 

So can you use radiators with your potential new air source heat pump?

Yes. 

However the next question is, can you use your radiators that you have been using with your current heating system?

This is where it gets a little more tricky.

The most ideal situation would be to use underfloor heating with your heat pump and if you were building a new home this would be a lot easier to implement. However, it is not always feasible to start ripping all of your floorboards up. For this reason radiators are the next best option.

Radiators have to be sized for the correct flow temperatures. A typical boiler works with a flow temperature of between 70-80 degrees whereas a heat pump’s flow temperature is typically around 35-50 degrees.

As the flow temperature decreases the larger the heat emitting surface area needs to be. Heat pumps work more efficiently at lower temperatures.

They are designed to provide a lower heat over a longer period of time so therefore they typically need a larger sized radiator than with a gas central heating system. The chances are that your current radiators would be too small. You would then have the choice of replacing your radiators with larger sizes or adding more radiators to the system for your heat pump to work efficiently. 

What size radiators do I need?

There are three main factors. Apart from the flow temperature. That will determine what size radiators you need to compliment your ASHP and help it to run at its maximum efficiency. 

  • The size and shape of the room.
  • How well your home is insulated. A heat pump works best with a well insulated house, helping to keep the heat in the home. 
  • Ambient temperature of the room. You will more than likely require certain rooms to be warmer than others. For example, you may not want your bedroom as warm as your living room. 

Now this may seem a bit daunting and you’re thinking that you have no idea where to start.

Your engineer that installs your air source heat pump will be able to assess your flow temperature. The amount of heat loss and will be able to accurately size the best radiator to compliment your air source heat pump. To keep your home warm and comfortable all year round. 

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