Heat Pumps: What They Are and How They Work

27th Feb 2024
Daniel Frogley

Climate change is the single biggest issue facing the planet, so is it any wonder that we are looking for alternative ways to heat our homes.

Gas boilers have been the mainstay of home heating in the UK for generations. The modern gas boiler can trace its roots back to 1868, when Benjamin Waddy Maughan developed an instantaneous gas heater for domestic water. 

Even though his “Geyser” boiler had no flue and was prone to exploding, it was still popular. Britain’s love affair with the gas boiler has been a long time in the making. 

But, it seems the glory days are over for the humble gas boiler. Fossil fuels are polluting the planet, and we need a greener way to heat our homes. 

The Government is recommending a switch to heat pumps, in a bid to phase out gas boilers, as we move to more sustainable energy solutions. Say hello to the heat pump. 

What Is a Heat Pump?

A heat pump is a system that moves heat from one source to another via a compressor and liquid refrigerant. Think of it as a fridge in reverse. Instead of taking warm air and cooling it using refrigerant, it draws cool air and warms it. 

Heat is extracted from an outside source through the compressor and pumped inside your home. Heat pumps are more efficient and use less energy than other electrical methods of creating heat. Plus, you can reverse the process in the summer to provide air conditioning. 

Heat pumps are about 300% more efficient than gas, oil, and other electrical systems that create heat. Despite this, the UK lags behind other countries because of our fixation with gas boilers. 

This is about to change because the current Government is looking to consign gas boilers to the annals of history. To help with this transition, the Government has offered incentives to help the public move away from gas boilers.. 

Heat Pump Costs

Heat pumps are not a cheaper alternative to gas boilers. The typical cost of a gas boiler will set you back between £1,500 and £2,500, depending on the size of the boiler. You won’t get much change from £3,500 after you factor in the installation, but these costs are tiny when compared to heat pumps. 

Heat pumps start at about £9,000 but can cost as much as £25,000, depending on the type of pump, system requirements and size of your home. 

Maybe now we can see why gas boilers are so popular in the UK. However, with recent fuel price hikes, that popularity is waning. The government will soon offer £5,000 grants to help with purchasing and installing a heat pump, but it still doesn’t match the price of a gas boiler.

As technology improves and the take-up increases, the price is sure to drop, but that takes time. Weaning the British public off their reliance on gas is not going to be easy.

Different Types of Heat Pumps

Essentially, there are three types of heat pump - air source, water source and ground source - which you choose depends on many factors. 

Air Source

Air source heat pumps are the most popular because they are easier to install and involve minimal disruption to you and your home. 

They extract air from the outside and pump it through liquid refrigerant and a compressor to deliver heat inside your home. Air source heat pumps are probably the most accessible in terms of cost, making them the obvious choice when gas boilers are phased out.

Water Source

Water source heat pumps create heat by either drawing water through the system or a series of coils laid under the water. These coils are filled with a special refrigerant liquid that draws heat from the water. 

Water source heat pumps are between 300% and 600% efficient. So, for every pound you spend generating heat, the system returns £3 to £6 in efficiency savings. When you compare that to the average modern gas boiler at 95%, you can see why heat pumps are better for the environment and your wallet. 

Now for the elephant in the room. Not everyone lives near a body of water, making water source heat pumps a niche way to heat homes.

Ground Source

Ground source heat pumps operate on the same principle as water-based heating systems by using the planet’s natural resources to extract heat. So, how do they work exactly?

A series of coils filled with a liquid refrigerant (usually antifreeze and water) are laid under the ground just below the frost line. The temperature below the frost line (about four to six feet down depending on where you live) stays at a constant 50 degrees Fahrenheit in northern latitudes and 50 to 70 degrees Fahrenheit in the south.

These coils are laid either vertically or horizontally, depending on the geology and exterior space you have available. 

The advantage of ground source heat pumps (commonly known as geothermal heating) is they are green, cheap to run and as efficient as water source heat pumps. Also, the heat source will never expire as long as the world keeps turning.

The downside with ground source heat pumps is the cost. An entire system can cost between £15,000 and £25,000, which puts it well out of the reach of most people. You also need a decent-sized garden because the coils take up a lot of space when laid horizontally. 

The other issue with this form of heating is the suitability of your garden. Before geothermal heat pumps are installed, a thorough geological survey is needed to establish the feasibility of the ground conditions. 

Granite beneath your feet will seriously ramp up the costs because you will need specialist equipment to bore down into the rock.

Are Heat Pumps Safe?

Heat pumps are entirely safe because they don’t use combustion to heat your home. Compare this to a gas boiler which uses combustion, and you can see why they are safe. Also, when you consider that gas boilers create carbon monoxide, a heat pump is a much safer option.

Do Heat Pumps Require More Maintenance?

Heat pumps have fewer moving or mechanical parts compared to gas boilers, so they are less likely to break down. This makes them easier to maintain and manage.

Heat Pump Running Costs: Are They Cheaper?

Aside from efficiency savings, swapping gas for a heat pump means you spend on average about £500 less heating your home annually. With the increase in gas prices (and the likely upward trend for the longer term), you could see the savings increase further. 

Given that air source heat pumps typically last 15 years with the right amount of maintenance and servicing, a £500 annual saving equates to £7,500 over the lifespan of your heat pump. Working on the basis that a heat pump will cost around £12,000, it should pay for itself if you factor in the £5,000 Government grant. 

Water and ground source heat pumps can last for between 30 and 50 years, which means you are sure to get your money back in energy savings and reduced fuel costs. 

These kinds of savings make installing a heat pump a wise move. Not only does it save you money, but it also helps the planet. It’s a win, win for you and Mother Nature.

Advantages of a Heat Pump

  • Much safer than combustion systems.
  • Cheaper to run than gas or oil boilers.
  • Reduces your carbon footprint.
  • Gives a high energy to heat conversion.
  • Requires minimal maintenance.
  • Longer lifespan than gas boilers.
  • Eligibility for Government grants.
  • Provides air conditioning in the summer.

Disadvantages of a Heat Pump

  • High initial outlay.
  • Can be tricky to install. Some heat pump systems require geological surveys.
  • Some refrigerants are environmentally questionable.
  • Difficult and disruptive installation process for some types of heat pumps.
  • You will need special planning permission for water and ground source installations.
  • There are very few heat pump installers in the UK.  

Getting a Heat Pump Installed

The Government estimates that the number of qualified heat pump installers in the UK is between 3,000 and 4,000, but the industry widely disputes those statistics. According to Professional Heating and Plumbing Installer magazine (sounds like a fun read), there are only 600 qualified and accredited heat pump installers in the UK. 

Whatever the correct numbers, there is a bottleneck coming down the line, where demand will outstrip supply, putting strain on prices, materials, and timescales. When that happens, typically, prices will rise in the short term.

So, you might be waiting for a long time before you can switch from gas to a heat pump.

Will a Heat Pump Add Value to My Home?

A heat pump will add value to your home because of the energy savings and fuel efficiency of the system. The new owners will reap the benefits annually when they start paying their fuel bills. 

Air source heat pumps add the least value, although they still have a positive effect on the house price compared to gas boilers. Water source and ground source heat pumps add the most value because they are efficient and considered to be the greenest type of domestic heating.

Keep In Mind: Ground and water source heat pumps may add the most value, but they also cost several times the amount of a gas boiler.

A house with geothermal heating removes the uncertainty about fluctuating fossil fuel prices, which gas-heated homes still rely on. It puts you in control and keeps your energy bills at a sustainable level.