Are Heat Pumps for Everyone?
Possibly. The government scheme to encourage take up of heat pumps as part of the Net Zero challenge to counter human induced climate change (no, it’s not ‘just weather’) known as the Boiler Upgrade Scheme, offers £7,500.00 towards installation costs. Heavily marketed, the scheme and heat pumps as a technology have received extensive media coverage generating a degree of confusion around the efficacy of wide scale take up for a diverse range of property types and forms of construction.
Divesting from non-renewable energy usage seeks to move away from heating homes and providing hot water services via gas consumption towards renewably generated electricity. This is a steady process. Install a heat pump today and 38% of the electricity used to power the pump with will be through the burning of gas. Progress is being made – the generation of electricity in the UK from the burning of coal ceased in September 2024, 43% of electricity is from zero carbon sources, briefly hitting a peak of 87% in January 2025.
Heat pumps operate on a reverse refrigeration cycle utilising the generated heat to provide space heating and contribute to the provision of hot water services (via a thermal store). At optimum operation a heat pump will provide three units of energy to every one unit of input energy.
So, what’s not to like? The issue is not heat pumps per se; it is the built envelope that the service is being introduced into. Optimum heat pump operation is most effectively achieved in new builds where a truly airtight structure can be fabricated. Utilising Under Floor Heating (UFH) via the thermal mass of a screed to the ground floor slab and insulated cassettes to the first floor is most effective in utilising the (relatively) lower temperature heat from the heat pump. A sealed envelope requires the installation of a Mechanical Ventilation and Heat Recovery system to remove stale air and crucially to avoid the formation of mould.
Installing a heat pump to an existing unmodified property is likely to result in sub-optimal performance. What and how to modify an existing building requires careful consideration. Retro sealing a property is likely to lead to mould formation without the installation of a MVHR system. Retro fitting a MVHR system may not be a straightforward or an inexpensive operation. Historic England commissioned M&E consultants Max Fordham LLP to undertake a review of heat pump operation in a variety of preexisting buildings. This excellent report entitled ‘Heat Pumps in Historic Buildings. Air Source Heat Pump Case Studies – Small Scale Buildings’ provides a review and guide to strategies for successfully accommodating heat pumps in existing buildings and can be found at https://historicengland.org.uk/advice/technical-advice/building-services-engineering/installing-heat-pumps-in-historic-buildings/ .
Heat pumps for everyone…probably….but not without very careful consideration of the existing fabric of the subject property and likely significant expenditure in addition to the cost of the heat pump.
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