Air Source Heat Pump vs Gas Boiler

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Air Source Heat Pump vs Gas Boiler

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When weighing up an air source heat pump vs a gas boiler, the heat pump wins on efficiency, lifespan, and running costs on the right tariff, while a gas boiler wins on upfront cost and installation speed. For most homeowners replacing an aging boiler, a heat pump is the stronger long-term choice.

Our guide compares the two across how they work, efficiency, upfront and running costs, installation, maintenance, lifespan, and grants. It also explains why the electricity tariff you choose has such a big impact on which system is cheaper to run.

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Air Source Heat Pump vs Gas Boiler: Quick Comparison

Here's how the two systems compare at a glance before we break each factor down in detail.

Factor

Air Source Heat Pump

Gas Boiler

Efficiency

350–500% (SCOP 3.5–5)

Up to 90%

Upfront cost (installed)

£8,000–£18,000

£2,000–£4,000

Government grant

Up to £7,500 (BUS)

None

Running cost (typical 3-bed)

~£270/year on a time-of-use tariff

~£985/year

Lifespan

20–25 years

10–15 years

Maintenance

Service every 2–3 years

Annual Gas Safe service

Carbon emissions

~850kg CO₂/year

~2,500kg CO₂/year

Installation time

2–5 days

~1 day

Heating type

Steady, low-temperature

Fast, high-temperature

Cooling function

Yes (some models)

No

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ASHP vs Gas Boiler: How Each System Heats Your Home

The biggest difference between a gas boiler and a heat pump is where the heat comes from.

How a Gas Boiler Works

A gas boiler burns natural gas to heat water, which is then pumped to your radiators and taps. A combi boiler heats water on demand, while a system boiler stores hot water in a cylinder for use around the home.

Boilers produce high flow temperatures of 60–80°C, so radiators heat up quickly and deliver warmth in fast bursts.

How an Air Source Heat Pump Works

An air source heat pump extracts heat from the outside air, even in sub-zero temperatures, and uses a refrigerant cycle to raise it to a useful temperature. It runs on electricity rather than gas, with no combustion involved.

Heat pumps operate at lower flow temperatures of 35–45°C and deliver steady, consistent warmth rather than rapid bursts. Hot water is stored in a cylinder, so a hot water tank is part of the setup. Our guide on how air source heat pumps work explains the process in full.

Will My Home Feel Different?

A well-designed heat pump system keeps your home at a steady, comfortable temperature throughout the day rather than heating up fast and then cooling down. Many homeowners find the consistent background warmth more comfortable once they adjust to running the system at a lower temperature for longer periods.

Is an ASHP More Efficient than a Gas Boiler?

Efficiency is where the two systems differ the most dramatically.

A modern gas boiler is up to 90% efficient, meaning it turns 90% of the gas it burns into usable heat, with the rest lost through the flue. In reality, unless your boiler is fairly new, it's likely operating closer to 80% as efficiency drops with age.

An air source heat pump is 350–500% efficient, measured as a Seasonal Coefficient of Performance (SCOP). Most modern systems achieve a SCOP of 3.5–5.0, meaning that for every 1kWh of electricity they use, they produce 3.5–5kWh of heat.

This is possible because a heat pump doesn't create heat by burning fuel. It moves existing heat from the outside air, which takes far less energy than combustion.

Electricity costs more per unit than gas, so high efficiency alone doesn't guarantee lower running costs. The tariff you're on is what determines whether a heat pump is cheaper to run.

Gas Boiler vs Heat Pump: Installation Costs Compared

A heat pump costs more to install than a gas boiler.

A gas boiler replacement costs £2,000–£4,000 depending on the type and complexity of the job, such as switching from a conventional boiler to a combi or relocating the unit. An air source heat pump costs £8,000–£18,000 depending on your property size and system requirements.

However, the Boiler Upgrade Scheme offers a £7,500 grant towards installing an air source heat pump. The grant is not means tested, so anyone replacing a gas boiler can qualify. With the average ASHP installation costing around £12,000, the grant brings the total down to roughly £4,500.

The higher upfront cost is offset by lower running costs and a longer lifespan. A gas boiler lasts 10–15 years, so over the 20–25 year life of a heat pump, you'd typically replace a boiler at least once. Factoring in two boiler installations plus higher running costs narrows the lifetime cost difference considerably.

Running Costs: Is a Heat Pump Cheaper Than Gas?

The honest answer is that it depends entirely on your electricity tariff. On a standard tariff, a heat pump and a gas boiler cost roughly the same to run. On a time-of-use tariff, a heat pump is considerably cheaper.

On a Standard Tariff

On a standard electricity tariff of around 26p/kWh, a heat pump using 3,000kWh of electricity would cost around £780 per year. A typical 3-bed semi using 12,000kWh of gas pays roughly £985 per year on heating (at around 7p/kWh plus the standing charge). The heat pump is slightly cheaper, but not by enough to make a dramatic difference on its own.

On a Heat Pump Tariff

A heat pump tariff is a type of time-of-use tariff designed specifically for heat pump owners. It offers much cheaper electricity rates during several low-cost periods throughout the day (as low as 7–9p/kWh) in exchange for higher rates during peak hours.

Heat pumps are ideally suited to this because they run steadily and can be scheduled to do most of their heating when electricity is cheapest. A combi boiler can't take advantage in the same way, as it heats on demand in short, high-temperature bursts.

On a heat pump tariff at 9p/kWh, that same 3,000kWh of electricity costs approximately £270 per year. Remove the gas supply entirely, including the standing charge, and the net saving works out at £700–£750 per year.

Pair a heat pump with solar panels and battery storage and you can run it partly or fully on self-generated electricity, cutting running costs further still.

Installation Timeline

A gas boiler swap is quicker and simpler. A heat pump installation takes more planning, but it's straightforward with a qualified installer.

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  • 1

    Gas Boiler Installation

    A like-for-like boiler replacement typically takes one day, with minimal disruption and no external works. Switching the boiler type or moving it to a new location adds complexity, often extending the job to two or three days and increasing the cost.

  • 2

    Heat Pump Installation

    A heat pump installation takes 2–5 days depending on your property and any additional works. It requires a location for the outdoor unit with adequate airflow, a hot water cylinder, and possibly radiator upgrades to suit the lower flow temperature.

    A home survey will assess all of this before installation, and a good installer will handle radiator upgrades as part of the job where needed. An MCS-certified installer will also manage the BUS grant application and the DNO notification on your behalf.

  • 3

    What Your Home Needs

    To install an ASHP your property needs space for an outdoor unit, roughly the size of a small chest freezer, and space for a hot water cylinder in an airing cupboard, utility room, or garage. These units are getting smaller with each generation, and most aren't as large as people expect. Reasonable insulation helps the system perform efficiently, and your installer can assess whether any improvements are worth making beforehand.

Maintenance & Lifespan

A heat pump lasts longer than a gas boiler, though both need an annual service.

A gas boiler requires an annual Gas Safe service, which is important for both safety and warranty validity, and lasts 10–15 years. A heat pump also needs an annual service to maintain its warranty and keep it running efficiently, but it has no combustion parts or flue to maintain and carries no carbon monoxide risk. It lasts 20–25 years.

Over a 25-year period, you'd typically replace a gas boiler at least once, sometimes twice, for the same coverage one heat pump provides.

Which Is Right for Your Home? Heat Pump or Gas?

The right choice comes down to your property, your budget, and how long you plan to stay.

For most homeowners facing a gas boiler replacement, a heat pump is the stronger long-term investment. But if your current boiler is young and working well, there's no urgency to switch before you need to.

A Heat Pump Makes Sense If

  • Your boiler is over 10 years old. If you're facing a replacement anyway, the real cost comparison isn't £12,000 vs £0, it's £12,000 (minus a £7,500 grant) vs the £2,000–£4,000 you'd spend on a new boiler that lasts half as long.

  • You can switch to a heat pump tariff: Heat pump tariffs usually offer multiple low-cost periods through the day, which suits the way a heat pump runs. If you're able and willing to switch, a heat pump becomes genuinely cheaper to run than your gas boiler.

  • You have the space. Room for an outdoor unit and potentially a hot water cylinder is essential. Most homes with a driveway, garden, or utility space can accommodate both.

  • You're staying put for 8+ years. This gives the lower running costs time to offset the higher upfront cost.

  • You want to lower your carbon footprint. A heat pump produces roughly a third of the carbon emissions of a gas boiler for the same heating.

A Gas Boiler Might Still Suit You If

  • Your current boiler is only a few years old. If it's working well and running efficiently, there's little financial sense in replacing it before the end of its life.

  • You need the cheapest possible replacement right now. If your boiler has failed and budget is the priority, a like-for-like swap is the lower upfront cost, even if it works out more expensive over time.

  • You genuinely have no space. Flats and terraced homes without outdoor access or room for a cylinder may not be suitable for a heat pump right now. However, smaller indoor units designed for flats and terraced homes are in development.

  • Your home is poorly insulated and can't be improved yet. A heat pump in a draughty, uninsulated home will struggle and cost more to run. In that situation, improving insulation first is the sensible call. Get in touch and we'll let you know whether we can help with this.

Gas vs Heat Pump: Final Thoughts

An air source heat pump is the better long-term choice over a gas boiler. It's three to four times more efficient, lasts roughly twice as long, qualifies for up to £9,000 in grants, and on the right time-of-use tariff costs significantly less to run, saving a typical 3-bed home £700–£750 a year.

A gas boiler still has its place for those needing the cheapest immediate replacement or without space for a heat pump. But with grants closing the upfront cost gap and running costs falling on a suitable tariff, the case for switching has rarely been stronger.

Request a free quote and we'll assess whether a heat pump is right for your home.

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