How Heat Pumps Compare to Gas Boilers

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Choosing between a heat pump and a gas boiler for your home's heating system involves considering several factors including how each system works, their efficiency, costs, environmental impact, and suitability to your home. Here's a comprehensive comparison to help you decide.

How Heat Pumps Work

A heat pump operates like a fridge in reverse: it extracts heat from the outside air, ground, or water—even in cold weather—and transfers this heat indoors to warm your home. Using a refrigerant cycle, it absorbs ambient heat and compresses it to a higher temperature, then releases that heat inside through your heating system such as radiators or underfloor heating.

Unlike gas boilers that burn fuel to create heat, heat pumps move heat, making them highly energy-efficient.

Efficiency: COP vs Boiler Efficiency

• Coefficient of Performance (COP): Heat pumps typically have a COP between 3 and 5. This means for every unit of electricity consumed, they deliver 3 to 5 units of heat energy to your home—effectively 300% to 500% efficiency.
• Gas Boiler Efficiency: Modern condensing gas boilers operate at about 90% to 95% efficiency, converting almost all of the gas energy into heat but never exceeding 100% efficiency.

Because heat pumps move existing heat rather than generating it, their effective efficiency can surpass traditional boilers, although this depends on outdoor temperature and system design.

Typical Costs for a Mid-Sized Home

Upfront Costs

• Gas Boiler: Typically £2,000 to £4,000 (including installation), often requiring minimal changes to your existing heating system.
• Air Source Heat Pump (ASHP): Generally £8,000 to £18,000 before grants, including the unit, installation, and required system modifications (such as larger radiators and a new hot water cylinder). Grants like the UK Boiler Upgrade Scheme may reduce costs significantly.

Running Costs

• Gas Boiler: Annual heating and hot water costs usually range from £800 to £1,500+, depending on gas prices and home energy needs.
• Heat Pump: Although electricity is typically pricier than gas, a heat pump’s higher efficiency means running costs can be comparable, ranging roughly between £900 and £1,800 annually, influenced heavily by electricity tariffs, home insulation, and system efficiency.

Performance in Cold Weather

Heat pumps are designed to operate efficiently well below freezing (down to around -15°C or lower with specialized models). While efficiency (COP) decreases in colder temperatures, they still provide heat effectively, often better than direct electric heating.

Features like automatic defrost cycles prevent ice build-up on outdoor units. Some systems incorporate supplemental electric heaters or hybrid setups with boilers for extreme cold, though these are typically used sparingly.

Suitable Homes and Required Adjustments

Heat pumps perform best in well-insulated, airtight homes with lower heat loss. Upgrades to insulation (lofts, walls, floors, windows) significantly improve performance and comfort.

Because heat pumps operate efficiently at lower water temperatures (35-50°C), radiator systems may need to be modified or upsized to emit sufficient heat. Alternatively, underfloor heating or fan-assisted radiators can optimize heat delivery.

A new, larger hot water cylinder compatible with heat pumps is usually necessary, as heat pumps heat water more slowly than boilers.

Carbon Emissions Over Lifetime

• Gas Boilers: Directly emit CO2 by burning natural gas. Emissions remain constant through their lifespan.
• Heat Pumps: Indirect emissions depend on the electricity’s carbon intensity, which is decreasing steadily as grids integrate more renewables. Heat pumps' lifetime emissions will likely reduce substantially over time, making them a much lower carbon option, especially in regions with clean electricity.

Noise and Lifespan

• Heat Pumps: The outdoor unit produces a noticeable but generally quiet hum around 40–55 decibels (similar to a quiet fridge or conversation). Proper placement can minimize perceived noise. The indoor unit is typically very quiet.
• Gas Boilers: Operate quietly indoors with virtually no noticeable noise.

Regarding durability:

• Gas boilers usually last about 10 to 15 years.
• Heat pumps often have a longer lifespan, typically 15 to 20 years or more.

Summary of Key Trade-Offs

Final Advice

Heat pumps offer a sustainable, energy-efficient alternative to gas boilers, especially as electricity grids become greener. They require greater upfront investment and may need home improvements like insulation and radiator upgrades but provide lower carbon emissions and potential long-term savings.

Gas boilers remain a lower-cost, straightforward solution, particularly suitable for homes not ready for insulation upgrades or large system changes.

Consult with qualified installers and consider professional heat loss assessments to identify the best solution tailored to your home’s specifics, climate, and budget.

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References:

Heat pumps vs boilers: the key things you need to know - Which?
Heat Pumps vs Gas Boilers: Efficient Home Heating Solutions - The Eco Shift
Air Source Heat Pumps vs Gas Boilers - Cost, Efficiency and Savings | EDF
Gas Boilers vs Heat Pumps: A Comparison – Eco Friendly Home and Garden
What are heat pumps and can they save you money in the long-run? | The Independent
Total cost of ownership of heat pumps and policy choice: The case of Great Britain