Heat Pumps in London Period Properties: Feasibility, Performance, and What to Expect

Heat pumps have moved from niche technology to mainstream renovation specification over the past several years. Government incentives, rising gas prices, and improving equipment performance have combined to make them a serious option for London residential properties. The case for them in a well-insulated modern home is clear. The case in a Victorian or Edwardian period property is more nuanced.

Here is an honest account of heat pump performance in the London period property context.

What a heat pump is

A heat pump is a refrigeration device run in reverse. It extracts heat from the outside air (air source heat pump, ASHP) or from the ground (ground source heat pump, GSHP) and transfers it — amplified — into the heating system of the building. For every unit of electrical energy consumed, a heat pump delivers 2–4 units of thermal energy. This ratio is called the Coefficient of Performance (COP).

The COP varies with the temperature difference between the heat source and the heat distribution system. The smaller the temperature difference, the more efficient the heat pump. This has an important implication for period properties: heat pumps work best with low-temperature heat distribution systems, typically underfloor heating at 35–45°C flow temperature. They work less well with conventional radiator systems designed for 70–80°C flow temperatures.

The underfloor heating dependency

This is the central challenge for heat pumps in period properties. A Victorian terraced house was heated (or is now heated) by a gas boiler delivering hot water at 70–80°C to relatively small radiators sized for that flow temperature. If you replace the boiler with a heat pump without changing the radiators, you have a system that produces 45–50°C water going into radiators designed for 70–80°C. The radiators will not produce enough heat output to maintain comfortable temperatures in winter.

The solution requires one of:

1. 1.Replacing radiators with much larger units sized for the lower flow temperature — typically 2–3× the surface area of the existing radiators. This is expensive and disruptive, and large radiators are not always aesthetically acceptable in a period interior.

1. 2.Installing underfloor heating in the ground floor (and ideally all floors) — UFH at 35–45°C flow temperature is ideally matched to a heat pump. This is the best solution but requires significant construction work.

1. 3.Running the heat pump at higher flow temperatures — some modern heat pumps can operate at up to 65°C, accepting a reduced efficiency penalty. This allows existing radiators to be retained at some cost in operating efficiency.

The right approach depends on the renovation scope. In a whole-house renovation where the floors are being opened up, UFH is the natural choice. In a cosmetic renovation, a high-temperature heat pump with oversized radiators may be the most practical compromise.

Insulation requirements

Heat pumps are sized based on the heat loss of the building. A poorly insulated period property with high heat loss requires a larger heat pump and runs it harder, with lower efficiency. The economics of heat pump operation in a poorly insulated house are not compelling.

The practical implication: in a period property, heat pump installation should go hand-in-hand with insulation improvement — loft insulation, floor insulation, and where feasible, wall insulation. The combination produces a building with lower heat loss, a smaller heat pump, and lower running costs.

A heat pump in an uninsulated period property will run continuously on cold winter days, deliver modest CoP, and generate heat bills that may exceed those of the gas boiler it replaced.

Air source vs ground source

Air source heat pumps (ASHP): The standard residential choice. An external unit (similar in appearance to an air conditioning condenser) is mounted on a wall or on the ground in the garden. The unit is connected to the internal distribution system. External noise is a consideration — good quality units from Mitsubishi, Daikin, Vaillant, and Samsung are quiet enough for most residential situations.

For an ASHP in London, planning permission is generally not required under permitted development, subject to conditions: the unit must not be on the front elevation or roof visible from the highway, must be removed when no longer used, and the sound output at 1m must be below 42dB(A).

Ground source heat pumps (GSHP): Uses the relatively constant temperature of the ground (8–12°C year-round in the UK) as the heat source, accessed via horizontal ground loops or vertical boreholes. More efficient than air source (the ground is warmer than outside air on a cold winter day) but significantly more expensive to install. Horizontal ground loops require a large garden area (typically 2–3× the heated area of the house). Vertical boreholes are compact but cost £8,000–15,000 per borehole and require specialist drilling.

For most London properties, an ASHP is the practical choice. A GSHP is appropriate where the garden is large enough for horizontal loops and the client wants maximum efficiency.

Hot water

A heat pump requires a hot water cylinder — it cannot supply instant hot water in the way a combi boiler does. This is a spatial requirement that must be accommodated in the house. A hot water cylinder of 200–300 litres is typically required for a family household. In a renovation, the plant room or utility space should be designed to accommodate this from the outset.

The BUS grant

The Boiler Upgrade Scheme (BUS) provides a government grant toward the cost of installing a heat pump — £7,500 for an ASHP or GSHP at the time of writing. The grant is claimed by the MCS-certified installer (not the homeowner directly) and reduces the invoice price. The scheme has a finite budget and a sunset date; it should be verified as live before assuming it applies.

Heat pump installations must be carried out by an MCS-certified installer to qualify for the grant and to comply with the relevant building regulations.

Realistic costs

ASAAN's approach

ASAAN integrates heat pump installation planning into the broader M&E specification for renovation projects. Where a heat pump is the right choice, we ensure the heating distribution system and insulation programme are designed to support its performance.

If you are planning a renovation that includes heating system upgrade, contact us to discuss options for your property.