The Truth About Heat Pumps

Decarbonisation of the grid has a huge part in helping us to achieve the emissions reduction targets we have set ourselves. In doing so, it means heating our homes using electricity becomes an even more appealing alternative vs older carbon-heavy heating systems such as Gas or Oil. The most efficient way to do this is via a heat pump, so below, we hopefully will answer some basic questions you may have on these systems.

Img: Illustration of an air source heat pump

What are the different types of heat pump?

All of us have grown up with heat pumps in our houses, we just never used that term. A heat pump uses refrigerant to extract heat from a colder place and transfer that energy to a warmer place. A refrigerator in your kitchen uses this process to keep your food cool, hence why the back of your fridge will always be warm.

So, in essence, when we talk about Heat pumps as a heating system, we are talking about extracting heat from the outside (it doesn’t need to be warm to do this as there is always energy present) and using that energy internally to heat our homes.  

This energy can be extracted in a few ways, from either the Ground (a Ground Source Heat Pump GSHP) or from the Air (an Air Source Heat Pump ASHP) and that energy can be delivered via a wet system (radiators or underfloor heating) of via Air (forced air)

Pros and cons.

The internal heating system you choose is dependent on your personal choices, but in the UK, for the most part, a “Wet system” will be used.

When choosing between a Ground Source and an Air Source system, the deciding factors are usually costs and space. A Ground source system will more often than not provide a predictable operation in terms of efficiency as the soil is less likely to see fluctuations in temperature unlike with the Air. However, GSHPs are usually much more expensive to install, can require a large amount of space and can often be more challenging to maintain due to their construction.

Hence why an “Air Source to Water” heat pump is the most common system installed in the UK.

Who are they suitable for?

With the exception of the above limitations heat pumps should be a viable option for most properties. If they replace a Gas or Oil boiler, they will give significant carbon savings. If they replace a current electrically heated home, they will also offer carbon savings but this will be due to their efficiency rather than fuel source.

That last part is important, a gas or oil boiler may have an efficiency anywhere between 60 and 90% dependent on how old and how well the unit was installed. Electric resistant heaters will have an efficiency of 100%. That means for each kWh of energy you use with a 90% efficient gas boiler, you will generate 0.9kwh of heat.

An ASHP, on the other hand, may have an efficiency of 300% or higher, dependent on the installation, model, climate etc.

Let’s say for example, you switched out a Gas boiler with 90% efficiency and replaced it with an ASHP with an efficiency of 300%. Then let’s say you need 8000kwh of heat a year to heat your house.

With the gas boiler, you would need to use (8000/0.9) 8889kwh of energy to generate the heating demand.

With the ASHP, you would need to use (8000/3) 2667kwh of energy to generate the heating demand.

Why is this important?

If we focus on the carbon savings, it’s a no brainer, 2667kwh of electric vs 8889kwh of gas, so a big win for the ASHP.

However, when we look at current energy prices, the discussion is a little more complicated. In our example above the difference in cost for the gas (8889x 3.5pence/kWh) £311 vs the cost for the electricity (2667 x 34pence/kWh) £907, is considerable.

What this means is that although an ASHP can offer considerable carbon savings, its installation needs to be carefully planned around the actual heat loss of the property in question. In the above scenario, if that heat loss can be reduced, not only do we narrow the bridge between costs, we also reduce the amount of energy being used also, so a win win.

The above sets out to simplify this process, whereas in reality, there are many factors that can influence these options, so we would always advise speaking to a qualified professional before embarking on any measures.


What should you consider before installing?

Planning. Some properties may require planning consent before installing a heat pump often with limitations on where the external unit can be placed so always check with your local building authority.

Maintenance. The internal and external units should be installed in a location that allows easy to access for maintenance and that location shouldn’t compromise the operation of the system.

Noise. Many newer models are extremely quiet when running but do plan ahead for this in areas that maybe particularly vulnerable.

Existing Heating system. Depending on several factors a heat pump may require upgrades to the existing system, bigger radiators etc, or a change of heating system entirely, from electric panels to underfloor heating etc, so take good account of this.

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