Air Source Heat Pumps vs Gas Boilers (Compared With Real Examples)

Air source heat pumps can be the most popular type of heat pump on the market and there have been incentives by governments to help increase the uptake of heat pumps in both new and old homes.

On the other hand, gas boilers can be found already installed in millions of households and there is an extensive gas network to provide gas fuel to each of these homes.

Both modern air source heat pumps and gas boilers can be very efficient appliances in terms of using their respective fuels to generate heat, but even though they can both provide heating and hot water for a home there are several differences between them.

Gas boilers use gas as the source of fuel and use the combustion process to generate heat. Some energy is wasted in this process and generates some emissions. Heating can be provided very quickly, and a hot water tank may not be required as domestic hot water can be provided on demand.

Air source heat pumps only use electricity and move heat energy stored naturally in outside air to indoors to heat a home. There are no direct emissions and heat pumps can generate multiple times more heat energy than the electrical energy consumed. Heating is provided more slowly and at lower temperatures, and a hot water tank will be required if using for domestic hot water.

Both appliances use water-based central heating systems to heat a home, although the alternative type of heat pump system, air to air, can provide space heating rather than central heating.

We currently use an air source heat pump for heating and hot water for our home.

Our current home has an air source heat pump that provides both heating and hot water

It’s the air to water type of heat pump system, meaning that it works with a water-based central heating system in our home, consisting of radiators and underfloor heating. As it’s the air to water type, it also allows us to use our heat pump for hot water for taps, showers etc.

Air Source Heat Pump Hot Water Tank
The inside of our cupboard where all our main internal air source heat pump system apparatus is located

For our previous home we had a combi gas boiler system with radiators only.

Air Source Heat Pump & Gas Boiler

We’ve been using both systems for a number of years and understand the benefits that they can bring, but also their limitations.

In this article we explain more about the differences between air source heat pumps and gas boilers. We’ll also weigh the pros and cons to help you know which could be the better choice for your home.

Differences Between Air Source Heat Pumps & Gas Boilers

There are a number of differences between air source heat pumps (ASHPs) and gas boilers.

Both setups require a certain fuel for generating heat and they use different methods, materials, placements for doing so. They can also have different purchase, installation, running and maintenance costs.

If you’re unfamiliar with air source heat pumps you can check out our article on air source heat pumps explained where we go over our own heat pump in more detail.

Here are the main differences between ASHPs and gas boilers:

1) Air source heat pumps use electricity instead of gas

Air source heat pumps are electrical appliances and only use electricity as the form of power.

This means that an ASHP does not need to be supplied with any fuel such as oil or gas to work and simply need to be connected to the mains house electrical supply.

Our heat pump takes electricity from the internal garage it sits next to.

The electrical supply serving our heat pump

On the other hand, our old gas boiler was connected to both an electricity supply and gas supply.

See our article on air source heat pump electrical requirements for more information.

2) Air source heat pumps need to sit outside, while gas boilers are installed inside

To generate heat for a home, air source heat pumps move heat from outdoors to indoors and so the main external heat pump of an overall heat pump heating system needs to be located outdoors.

External heat pump units should be located in an open but secluded location so that they can extract heat from the air. This, among other factors, allows heat pumps to work as efficiently as possible.

Our ASHP is located down the side of our house and is connected to the internal heating apparatus with pipes.

Air Source Heat Pump
The location of our ASHP down the side of our house
Air Source Heat Pump Back
Heat is delivered indoors behind our heat pump through refrigerant in pipes

See our guides on how air source heat pumps work and where to install an air source heat pump for more information.

A typical gas boiler will sit inside a home, whether that’s up against an external or internal wall, or stored away in a cupboard.

Our gas boiler used to sit against the external wall in the kitchen.

Gas Boiler

As air source heat pumps don’t generate heat through combustion, they don’t need an oxygen supply, although they do need air in which to extract heat from. Oxygen, however, plays a crucial role in the burning process of all gas boilers and so typically must have a dedicated fresh air supply.

3) Air source heat pump systems can have a higher upfront cost

As gas boilers are already commonplace in many homes and their technology has been around for years, their purchase and installation costs are often less expensive than new air source heat pump installs.

Furthermore, with gas central heating systems so common in households, upgrading to a more modern and efficient boiler can be much less expensive than installing a new ASHP unit and upgrading the indoor heating system alongside it.

We cover how much an air source heat pump can cost to purchase, install and run in another article here, but a new full installation could cost 5-figures.

There are however many financial and other incentives to upgrade to an air source heat pump from a boiler such as the UK’s Boiler Upgrade Scheme, which can help reduce initial costs.

Our ASHP was installed when the house was built and so we’re unsure of how much the total heat pump system cost. However, we can assume that it cost more than a gas system would have cost.

A heat pump system typically costs more to install than a gas boiler

While air source heat pump installations may have a higher initial cost compared to gas boiler systems, there can also be a big difference in the cost of energy and therefore running costs.

Gas can be, on average, cheaper than electricity in terms of energy costs from your provider. However, as air source heat pumps can be much more efficient than gas boilers (which we discuss more about below), the running costs for either a gas boiler or an ASHP can be very similar.

As a result, air source heat pumps can demand overall higher costs and should therefore be considered as a long-term investment to be cost effective.

Gas prices are likely to continue to rise into the future, making running an electrical air source heat pump more cost effective in comparison.

4) Air source heat pumps are more efficient

Air source heat pumps can generate multiple more times more heat energy than the electrical energy consumed.

This is often referred to as the Coefficient of Performance (COP) or for cooling the Energy Efficiency Ratio (EER), or their seasonal counterparts (SCOP & SEER).

In ideal conditions an air source heat pump can be 300% or 400% efficient. For example, our heat pump can have a COP of over 4 (over 400% efficient) in the most ideal conditions.

Air Source Heat Pump Plate
The COP for our heat pump and two different air temperatures

However, it’s not always going to be the ideal conditions for a heat pump to work in and outdoor air temperature can significantly affect the efficiency of an ASHP.

At lower outdoor air temperatures there is greater temperature difference between the outdoor and indoor air temperatures, and so more power input is required to generate the same level of heat, therefore reducing the performance coefficient/ratio.

Air Source Heat Pump Power Input
Power input is increased at lower air temperatures for our air source heat pump, which won’t be a problem for a gas boiler

In comparison, a gas boiler will be less than 100% efficient because not all the energy within the fuel will be converted to useable heat, and there will be some energy wastage.

Our article on air source heat pump efficiency covers this topic in more detail.

5) Gas boilers are only used for heating and hot water, not cooling

Certain types of heat pump systems are able to efficiently cool a home as well as heat.

Air to air heat pump systems, which provide space heating through heated air, can also be very effective as a cooling system by reversing the heating process.

Gas boilers can only provide heating and hot water. Another system for cooling a home would be required, such as air conditioning units.

Air Source Heat Pump Mount
Gas boilers can’t provide cooling and so another system such as air conditioning units will need to be used

Air to air heat pump systems (which work with air handling units) can be more common in warmer climates where cooling is more of a necessity. In milder climates, such as the UK where we live, air to water systems (which work with water-based central heating) are the most common form of ASHP.

Another thing to note is that air to water heat pump systems aren’t typically set up to provide cooling. They can however be used to provide domestic hot water because it’s a water-based setup.

On the flip side, air to air heat pump systems can be just as effective for cooling as heating but can’t be used to provide hot water and so another system would be required.

In our old home we simply had a gas boiler for heating and hot water, with no form of cooling.

See our main article on air source heat pump cooling for more information.

6) Air Source Heat Pumps Have Slower & Lower Heat Output

Air source heat pumps work by extracting heat from outside air. Although this can be a very effective method of heating a home overall, it can take time to extract this heat.

As a result, the output temperature from an ASHP can be much lower than that of a gas boiler and therefore a heat pump will need to be run for a longer period of time to reach for it to produce the same internal temperatures.

As air source heat pumps are so efficient, this doesn’t necessarily affect the running costs but means that the internal heating apparatus need to be able to work alongside how a heat pump performs and release the lower temperature heat into a home as efficiently as possible.

That’s why ASHPs will be paired with underfloor heating and modern and large radiators. Their large surface area helps to release the heat more effectively.

Air Source Heat Pump Radiator
The use of large surface area radiators is more important with air source heat pumps than gas boilers

As air source heat pumps deliver lower temperature heat and at a slower rate, there is an increased importance put on the insulation levels of a house.

A home that isn’t well insulated can lose heat too quick for a heat pump to bring indoor temperatures up to a sufficient level.

A gas boiler is able to provide very hot water and central heating within a very short period of time.

Furthermore, during colder temperatures there’s less heat to extract from the outside air and so the performance of an air source heat pump can be affected. At extreme temperatures this can affect output temperatures.

For example, the graph below shows how the output water temperature from our heat pump lowers at outdoor air temperature reach the minimum operating temperature of our heat pump of -20°C (-4°F).

How the output water temperature from our heat pump is affected by decreasing outdoor air temperatures below freezing

However, for milder climates such as the UK these extreme temperatures can be much less common and so output temperatures from an ASHP realistically may not be affected regularly.

A gas boiler will typically be able to generate the same level of internal heat no matter the outside temperature.

7) Air Source Heat Pumps Will Require A Tank For Hot Water

As air source heat pumps deliver heat more slowly and at lower temperatures, they can’t provide domestic hot water on demand and so must be paired with a suitable hot water storage tank.

The use of a hot water tank allows domestic hot water temperatures to be built up over time so that they’re at temperatures users would deem as ‘hot’.

We have a hot water tank as part of our heat pump system in which our hot water is stored.

Air Source Heat Pump Water Heater Tank
Our heat pump requires the use of a hot water storage tank, where as our previous combi gas boiler didn’t need one

A hot water tank suitable for use with an ASHP system may also have one or more built-in electric immersion heaters to help keep temperatures topped up when demand for hot water is high.

A traditional gas boiler may also be used alongside a hot water tank, but the use of a combi-boiler allows hot water to be provided on demand without the need for a storage tank.

See our article on air source heat pumps and hot water tanks for more information.

8) Gas Boilers Have Direct Emissions

Gas boilers use the combustion of gas as fuel to generate heat.

This means that there will other byproducts of the emissions process, such as waste gases.

A gas boiler therefore needs a flue to vent waste gases to the outside air. By heating a home with a gas boiler, these waste gases are being released into the atmosphere.

On the other hand, air source heat pump are electrical appliances and don’t generate heat through combustion.

As a result, heat pumps don’t directly generate emissions, although the electricity used to power an ASHP may have come from a non-renewable source of energy with its own emissions.

An air source heat pump could be combined with solar panels for a more sustainable system.

Pros and Cons of Gas Boilers & Air Source Heat Pumps

Advantages of Gas Boilers

  • Quick heat. Burning gas is currently one of the quickest ways to heat your home.
  • Higher temperature output. A gas boiler can have a higher temperature output thanks to using the combustion of fuel to deliver quick and high temperature heat.
  • Less expensive to install. A gas boiler install is typically cheaper in comparison to an air source heat pump install, especially when an existing boiler is being replaced and the indoor heating system is already setup.
  • Still effective at very cold temperatures. As gas boiler won’t be affected by freezing outside temperatures.

Disadvantages of Gas Boilers

  • Higher emissions. A gas boiler will emit waste gases into the atmosphere during operation.
  • Can’t be used for cooling. Gas boilers can only be used for heating purposes and another system would be required for cooling.
  • Need both gas and electricity. A gas boiler will require both a gas and electrical supply, where as an air source heat pump only required electricity to work. Not all areas will have access to the gas network.
  • Gas boilers being phases out. As countries look to meet emissions targets, gas-powered heating appliances are looking to be phased out.

Advantages of Air Source Heat Pumps

  • Can help save money in the long run. Increasing gas energy costs can help make the running of an air source heat pump more affordable than a gas boiler.
  • Both air to air and air to water systems. Whatever your existing or proposed internal heating setup you can choose between either an air to water or air to air heat pump system. Air to air heat pumps will work with a space heating based internal setup such as air handling units and ducts. Air to water heat pumps will work with a water-based central heating setup such as radiators and underfloor heating.
  • Choose ductless or ducted ASHPs. Air to air heat pumps can work with both ducted and ductless systems. If a home has existing ductwork, a central air handling unit can be used for whole-house heating and cooling.
  • Air source heat pumps both can heat and cool a space. They’re excellent for year-round performance. You can quickly adjust the thermostat to make the building much more comfortable, unlike a gas boiler that only provides heat. However, a downside to this is that only air to air heat pumps are set up for cooling, not air to water heat pump systems.
  • Extremely efficient. Air source heat pumps are much more efficient on paper compared to gas boilers and can provide multiple times more heat energy compared to the electrical energy consumed. A gas boiler will have some wastage through the combustion process and will be less than 100% efficient.

Disadvantages of Air Source Heat Pumps

  • Higher upfront costs. Installing an air source heat pump system is typically more expensive than installing a gas boiler system, and if moving from an existing gas boiler to a heat pump, the internal heating apparatus may also need to be upgraded to work with a heat pump, which can be added cost. However, this upfront cost needs to be weighed up against all the other benefits of ASHPs.
  • Lower & slower heat output. Air source heat pumps deliver lower temperature heat and at a slower rate compared to gas boiler heating systems. However, this can be worked around by heat pumps running for longer periods of time and using modern and efficient heating equipment such as underfloor heating and large radiators.
  • Increased electricity energy costs. A heat pump will consume more electricity than a gas boiler, albeit not use any gas as the fuel.
  • Noise. External air source heat pumps need to be located outside and can make noise during operation due to the fan(s). This noise needs to be considered when choosing where to install an ASHP and also for neighboring properties. See our article on air source heat pump noise for more information.
  • Can’t always provide domestic hot water. Air to air heat pumps can’t be used for domestic hot water and so another system must be used. Air to water heat pumps systems however, which work with water-based central heating rather than space heating, can work alongside a hot water storage tank to provide hot water.
  • Sufficient home insulation required. A home needs to have a good level of insulation to make the most out of a heat pump. If insulation is insufficient, heat can be lost from a home as quickly as it’s released by an ASHP heating system.
  • Long term investment. Air source heat pumps should be considered as a long-term investment to help make them a better overall financial commitment.

See our article on the pros and cons of air source heat pumps for more information.

Air Source Heat Pump Or Gas Boiler?

If you’re thinking about getting a gas boiler or an air source heat pump, consider the following:

  • Gas boilers will require a gas supply to the home. Air source heat pumps only need an electrical supply.
  • Gas boilers are likely to be phased out in the future.
  • How long will you be living in your home? You can help to future proof your home by installing an air source heat pump, with the downside being increased upfront installation costs.
  • There are incentives for installing air source heat pumps, such as the UK’s Boiler Upgrade Scheme.
  • The current level of insulation in your home, and the age and efficiency of your current heating system to work with a heat pump.
  • The space requirements for an ASHP system, both indoors and outdoors.
  • A heat pump can need to work harder in colder temperatures, with increased energy usage, and noise levels may increase.

Further Reading

Air to Air & Air to Water Heat Pumps Explained

Do You Need A Boiler With An Air Source Heat Pump?

Parts Of An Air Source Heat Pump System Explained

How An Air Source Heat Pump Works

Can An Air Source Heat Pump Replace An Oil Boiler?