ECD Insights: What comes first, fabric or heat pumps?

Cut away of Cambridge housing retofit showing heat pumps and fabric first

May 2, 2024


What comes first: fabric or heat pumps?
By Loreana Padron
May 2024

Many in the industry are currently debating if heat pumps should be installed as a first step in homes where fabric measures (such as internal and external insulation) are too costly or disruptive (or there are technical, heritage or planning constraints) or simply when gas boilers break down. This heat pump first notion comes from the need to replace fossil fuel heating now (for space and hot water) and make a big jump in the decarbonisation of our homes. Now that the efficiency or COP (coefficient of performance) of heat pumps is getting closer to the difference in price between gas and electricity, heat pumps can potentially cost the same to run as gas boilers. These costs, however, may still be too high for residents in fuel poverty and, on their own, heat pumps will not improve homes with condensation and mould – in fact, it could make things worse if the homes are heated less.

The cost-effectiveness of heat pumps relies on their efficiency (COP), which is directly related to the water flow temperature in the system. The lower the temperature, the more efficient and cheaper they are to run. The question then is: what do we need to do in the building to create the conditions to be able to heat with low flow temperatures? This can be done by reducing the heat losses (and therefore the heat load) or by increasing the size of the radiators, or both. Heat pumps can cost the same to run as an 85% efficient gas boiler, only if their COP is about 3.4, which generally requires a flow temperature of 45⁰C.

If heat pumps are installed on their own, on leaky and cold homes with small radiators, then they will need to run at high temperatures and low efficiencies (COP), which can result in uncomfortable low temperatures and/or high energy bills. If heat pumps are installed at scale under these unfavourable conditions, they need more energy to run and will apply even greater pressure on the electricity grid, which needs to cope with its own infrastructure improvements and increased capacity, not even mentioning the public outrage at heat pumps if electricity bills rise abruptly.

Installing heat pumps as a first measure is all well and good if decarbonisation is the only goal when retrofitting homes; but this is often not the case. For some residents and clients, the main motivation is to reduce carbon emissions, but for others it is to improve comfort and health and/or to reduce energy bills. We, therefore, need to be clear of these motivations, as well as the considerations above, so that we can advise our clients in the best possible way.

Rather than fabric or heat pump first, we must place the priority on the residents. Each home should have a specific and tailored retrofit plan based on people’s health, wellbeing and affordability. 85% of homes still use gas for heating and/or cooking and, whilst it is imperative to decarbonise the housing sector, it must also be a priority to do so focusing on the people and communities that are being involved. Therefore, decarbonisation in the domestic retrofit sector must come together with reduction of fuel poverty, improved comfort and health, as well as providing future climate resilience.

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