What Affects Heat Pump Efficiency?

Unlike gas boilers, air-source heat pumps can work at more than 100% efficiency – the higher the efficiency of the heat pump, the less power it needs to output the same heat for your water & radiators. Using less power for the same heat output translates into two key benefits:

1. Higher efficiency is better for the environment because less power needs to be generated from fossil-fuel sources
2. Using less power means lower energy bills

Air Source Heat Pumps (ASHPs) can actually work at efficiencies between (and frequently over) 300-400% – but only if they’re installed & designed thoroughly by real experts. This 300-400% figure is usually the average efficiency rating over a whole year, and we do everything in our power to squeeze as much efficiency from your system as possible.

But what affects heat pump efficiency? Here are all the things we discuss:

Outside temperature

Your home’s ‘heat loss profile’

Radiator sizes

Heat pump & radiator settings

Air Source Heat Pumps work by maximising the difference in temperature between a refrigerant liquified gas and the outside air. The refrigerant gas can get as low as -35°C, so whenever the ambient air temperature is above that figure, the heat pump will be able to extract heat from the air. 

They can extract heat from the outside air in temperatures down to -28°C, but the warmer the outside temperature, the more efficient your system will be.

So it’s clear why ASHPs are so suitable for the climate in most of the UK’s regions! The ambient air temperature rarely gets below 0°C in large parts of Britain.

For added peace of mind, we design all our systems down to -5°C. MCS standards & requirements state that the system should be designed to -1.8°C for a UK installation – which means we go the extra mile to ensure you’re kept warm for those few occasions when the temperature does drop. As a bonus, we also ensure your home is warmer than the requirements set out by MCS.

You may be wondering if they’re still better than a traditional boiler given the seasonal changes in performance. Well, an air source heat pump’s efficiency is lower during the coldest times of year because there’s less of a temperature difference to tap into.

But, when the ambient air temperature is higher during the hotter summer & spring months, the heat pump system can operate at a much higher efficiency. Making the average performance of a heat pump over the whole year much more efficient than a boiler – we expect this to be between that key 300-400% mark.

The outside temperature is, however, not something you can control – but something you can control is your home’s ‘Heat Loss Profile’ (HLP).

When heating up a space, you need to account for how much (and how quickly) that space loses heat. Some materials, like masonry, take longer to absorb heat and hold on to it for much longer than, say, wood panelling. As a rule of thumb, the denser the material, the more it reflects heat.

The heat loss profile of your home is therefore largely a measure of how well insulated it is. And this is, in many cases, a balancing act between being able to absorb heat from the sun while also limiting how much heat escapes from your home.

Luckily, most of the heat in a reasonably insulated home is lost through windows and the roof – both of which are relatively straightforward to insulate by upgrading to newer, thicker windows and adding loft insulation.

What’s more, any walls shared with neighbours don’t usually lose a great deal of heat because neighbours usually heat their side of the wall too.

By making sure your home loses as little heat as possible, you make sure that your boiler doesn’t need to provide as much heat as regularly. So, rather than cycling repeatedly, your air source heat pump can operate at a much lower, more constant flow temperature to trickle heat into your home throughout the day to keep it consistently comfortable.

The size of a radiator affects how much heat it can effectively radiate. That is, hot water passes through a radiator and makes the metal of the radiator hot – the more surface area a radiator has, the more heat it can release at any one moment.

How much heat a particular radiator can release depends a lot on the design and style of the radiator.

Gas boilers tend to be run at a much higher “flow temperature” (the temperature flowing through your central heating system’s pipes & radiators) than ASHPs, so smaller radiators are installed because, with a higher input temperature, they can output the required amount of heat.

The key for air source heat pump efficiency, however, is being able to run the flow temperature as low as possible. This is why we sometimes recommend upgrading your home’s radiators.

Sticking with small, old single-panel radiators won’t stop your system from running, it’ll just run at a lower efficiency.

For the most part, a key benefit of an air source heat pump is that you can set it and forget it – but it’s worth staying aware of how you’re using your heating for the first while.

Our engineers will always leave you with the best settings to maximise efficiency, so you shouldn’t ever have to adjust the settings, but there may be efficiency gains if you change your home’s temperature. Lower thermostat temperature, for example, can often increase your SCOP.

The three main ways to maximise system efficiency through the way you use the system are:

1. Get the weather compensation right
2. Check that your hot water’s not set too hot
3. Make sure all radiator valves are turned on (even in rooms that don’t need to be heated)

If you’re thinking of making the leap to completely sustainable heating with an Air Source Heat Pump or you’re having problems with your system, our expert engineers are always happy to help. Let’s talk.

Give our experts a call on 01255 821443. Alternatively, you can fill out a call-back request form and a member of the team will be in touch.