Gas Boiler vs Heat Pump for London Properties in 2025: A Practical Comparison

Gas Boiler vs Heat Pump for London Properties: The Honest Picture

The push toward heat pumps as a replacement for gas boilers is real, and the technology has matured significantly. However, the practical reality for the majority of London properties in 2025 is more nuanced than the headlines suggest. This comparison covers how each technology works, the specific constraints London properties present, running costs at current energy tariffs, and an honest verdict on which makes sense for different property types.

How Heat Pumps Work

An air source heat pump extracts latent heat from outdoor air and compresses it to raise the temperature, then delivers that heat into the property through radiators or underfloor heating. The key operational difference from a gas boiler is the flow temperature: a heat pump delivers heat at 45 to 55 degrees Celsius, compared with 70 to 80 degrees Celsius for a typical gas boiler. This lower flow temperature is more efficient for the heat pump but has important implications for the existing heating system.

Ground source heat pumps extract heat from the ground via buried loops or boreholes. They are more efficient than air source units but require significant outdoor space for the ground array and substantially higher installation costs. Ground source is rarely practical in a London setting.

The London Flat Reality

Most London properties are flats, and flats present specific barriers to heat pump adoption. Air source units require outdoor space with at least one metre of clear space on all sides for airflow. Many London flats, particularly those in converted Victorian and Edwardian terraces, lack this space entirely. Where an outdoor location is available — a rear courtyard or flat roof — planning considerations often apply.

Under permitted development rights, air source heat pumps can be installed on houses without requiring a full planning application, subject to specific conditions including the one-metre setback rule and a maximum of one unit per property. Crucially, permitted development does NOT apply to flats. Any flat installation requires a formal planning application, which adds time, cost, and uncertainty to the project. Listed buildings of any type require listed building consent.

Radiator Sizing: A Hidden Cost

Existing radiators in most London properties were sized to operate at a flow temperature of 70 to 80 degrees Celsius. At the lower flow temperatures a heat pump delivers, the same radiator outputs significantly less heat into the room. Many properties will need larger radiators, additional radiators, or underfloor heating to compensate. The cost of this upgrade can add £2,000 to £5,000 to the overall project, and in some properties with solid walls or tile floors, the disruption is substantial.

Running Costs at 2025 Energy Tariffs

Electricity costs approximately 3.5 times more per kilowatt-hour than gas at 2025 standard tariff rates. A heat pump with a coefficient of performance of 3 delivers 3 kilowatt-hours of heat for every 1 kilowatt-hour of electricity consumed. The net running cost is therefore broadly similar to a gas boiler at current tariff ratios. The advantage of a heat pump on running costs depends heavily on the property being well insulated: a poorly insulated property will see the coefficient of performance drop, eroding the cost advantage. In well-insulated properties with underfloor heating, a heat pump can deliver meaningful running cost savings.

Boiler Upgrade Scheme: The Government Grant

The Boiler Upgrade Scheme offers a £7,500 grant toward the installation of an air source heat pump as of 2025. A typical installed cost of £10,000 to £15,000 reduces to £2,500 to £7,500 after the grant. This substantially improves the financial case, but the grant does not eliminate the need for radiator upgrades or resolve the planning constraints affecting flats.

Verdict: Which Technology Is Right for Your London Property?

A heat pump makes strong sense for a well-insulated detached or semi-detached house in London with adequate outdoor space, modern double or triple glazing, and loft and wall insulation already in place. The combination of the Boiler Upgrade Scheme grant and lower running costs in a well-prepared property creates a genuine long-term financial case.

For the majority of London flats and for older terraced houses with solid walls or poor insulation, a gas boiler remains the practical and cost-effective choice in 2025. The planning restrictions on flats, the absence of outdoor space, and the cost of radiator upgrades make heat pump installation impractical or uneconomic for a large proportion of the London housing stock. This assessment may change as electricity tariffs converge with gas and as the planning framework for flats evolves, but in 2025 the gas boiler remains the default choice for most London homes.