Why Insulation Must Come Before a Heat Pump in a London Home
Installing a heat pump in an under-insulated London home results in high running costs and poor comfort. This guide explains the relationship between insulation and heat pump performance, which insulation measures to prioritise in a London home, and the order in which improvements should be made.
The Relationship Between Insulation and Heat Pump Performance
The efficiency of an air source heat pump is directly linked to the flow temperature at which it operates, and the flow temperature needed to heat a building is directly linked to the insulation level of that building. A well-insulated London home loses heat slowly, and the heat pump can maintain comfort at a low flow temperature because only a modest amount of heat needs to be supplied continuously to replace what is being lost through the fabric. A poorly insulated London home loses heat rapidly, and the heating system must supply a much higher continuous heat output to maintain comfort, requiring a higher flow temperature from the heat pump.
Heat pump efficiency falls significantly as flow temperature rises. An air source heat pump delivering heat at 35 degrees Celsius might achieve a COP of 4.0 or higher. The same heat pump delivering heat at 55 degrees Celsius might achieve a COP of only 2.0 to 2.5. For a London home with a high heat demand that forces the heat pump to operate at elevated flow temperatures, the heat pump will consume much more electricity for each unit of heat delivered, pushing running costs to levels that may exceed those of the gas boiler it replaced. Installing a heat pump without first addressing the insulation of the building is the most common mistake made in the transition from gas to heat pump heating.
Priority Insulation Measures for London Homes Before Heat Pump Installation
The insulation measures that deliver the greatest reduction in heat demand for the least cost should be prioritised before a heat pump is installed. For most London homes, the hierarchy of measures runs from lowest cost and disruption to highest. Loft insulation is the first priority: a London home with less than 100 millimetres of loft insulation should have this increased to 270 millimetres as a minimum before any other measure is considered. The cost is low, the improvement is significant, and the installation is straightforward. If the loft is accessible and the hatch is of adequate size, loft insulation can be installed in a day with minimal disruption to the occupants.
For London homes with cavity walls, cavity wall insulation is the second priority. Cavity walls are found in properties built between approximately 1920 and 1995. Cavity wall insulation is injected into the cavity from the outside by drilling small holes in the mortar joints, injecting insulating material, and repointing. The process takes a few hours for a typical semi-detached house and has no impact on the interior of the property. The improvement in thermal performance is significant: cavity wall insulation typically reduces heat loss through the walls by 30 to 40 percent.
Solid Wall Insulation for London Victorian Terraces
For London Victorian terraces and Edwardian properties with solid walls, the insulation options are more expensive and more disruptive than for cavity wall properties. External wall insulation requires fixing insulation boards to the external face of the building and applying a render or cladding finish. In London conservation areas and on listed buildings, external insulation may require planning consent. Internal wall insulation involves fixing insulation boards or stud work with insulation to the internal face of the external walls, reducing room size slightly and requiring the relocation of electrical sockets and the reinstatement of skirtings and architraves.
The cost of solid wall insulation in London ranges from approximately 8,000 to 15,000 pounds for external insulation on a typical three-bedroom terrace, or 4,000 to 8,000 pounds for internal insulation. These costs are significant but are justified when the alternative is a heat pump system that operates inefficiently due to high heat demand. The Great British Insulation Scheme and the Energy Company Obligation scheme both provide funding for insulation in London homes that meet income or property criteria, and London borough councils administer local area schemes that may provide additional support.
The Correct Order of Improvements for a London Heat Pump Installation
The correct sequence for a London homeowner transitioning from gas to heat pump heating is insulation first, then radiator sizing review, then heat pump installation. The insulation improvements reduce the heat demand of the building, which allows the heat pump to be sized smaller and to operate at lower flow temperatures with higher efficiency. The radiator sizing review ensures that the heat emitters can deliver adequate heat at the lower flow temperatures of the heat pump system. Only once these preparatory steps are complete should the heat pump be installed and commissioned. Prestige Engineers provide whole-house heating improvement consultations for London homeowners and can produce a staged improvement plan that addresses insulation, radiators, and heat pump installation in the correct order for your specific property.