Air Source Heat Pumps for London Landlords — A Realistic Guide

Are Heat Pumps Viable for London Rental Properties?

Air source heat pumps (ASHPs) have become a significant topic for London landlords in 2024-2025, driven by government grants, EPC minimum standards (C-rating required from 2025 for new tenancies under proposed legislation), and tenant demand for lower energy bills. But they are not suitable for all London properties, and the economics require careful analysis.

The Boiler Upgrade Scheme Grant

The Boiler Upgrade Scheme (BUS) provides a £7,500 grant towards air source heat pump installation. This grant is available to:

• Owner-occupiers and landlords
• Properties replacing a gas, LPG or oil boiler
• Properties with a valid EPC (unless listed building or no requirement)
• Properties with no outstanding loft or cavity wall insulation recommendations on the EPC (or where these are not practical)

At typical London ASHP installation costs of £10,000-15,000, the £7,500 grant reduces net cost to £2,500-7,500 — making the economics much more attractive.

London Property Types: Suitability Assessment

Victorian and Edwardian Terraces and Semis

These form the majority of London rental stock and present challenges for heat pumps:

• Insulation: Most have solid brick walls (no cavity) — expensive to insulate externally or internally. Without adequate insulation, heat pump efficiency (coefficient of performance/COP) drops significantly in cold weather.
• Radiator size: Victorian-era radiators are often undersized for heat pump flow temperatures. Heat pumps work at lower flow temperatures (45-55°C) than gas boilers (70-80°C). Undersized radiators cannot deliver enough heat — requiring replacement or additional units.
• Garden space: Most London terraces have small rear gardens adequate for an outdoor unit, though many have shared side access paths that complicate positioning.
• Verdict: Viable in well-insulated examples; challenging and expensive in uninsulated Victorian terraces without significant upgrade investment.

Post-War Purpose-Built Flats

ASHPs are generally not suitable for flats because: the outdoor unit requires positioning on the building exterior (requiring freeholder/leaseholder approval), and air-to-water heat pumps typically serve whole properties rather than individual flats. Air-to-air (heat pump split systems) are an option but do not provide domestic hot water.

1930s Semis and Detached Properties

Cavity wall insulation is usually feasible. Better garden access for external unit. These properties are the most straightforward for ASHP installation in the London rental market.

Running Cost Comparison: Gas vs Heat Pump

At current (2025) energy prices:

• Gas boiler: ~6p per unit of heat (at 85% efficiency, gas price 7p/kWh)
• ASHP in well-insulated property (COP 3.0): ~7.5p per unit of heat (at 30p/kWh electricity, COP 3.0)

This means heat pump running costs are currently 20-25% higher than gas in London conditions for typical rental stock — primarily because the electricity-to-gas price ratio (approximately 4:1) outweighs the COP efficiency advantage. This changes if electricity prices fall relative to gas, or with the heat pump tariff discount available from some suppliers.

EPC and Minimum Energy Efficiency Standards

Installing an ASHP typically improves a property's EPC rating because the SAP methodology favours lower carbon intensity of electricity over gas. A Victorian terrace rated EPC D with a gas boiler may achieve EPC C after ASHP installation plus basic insulation improvements.