There is much debate at the moment amongst advocates of both heat pumps and hydrogen boilers, but the fact is the UK is going to need both to decarbonise domestic heating.
It is an important discussion – about 20% of UK carbon emissions are generated by domestic heat – but vested interests and entrenched positions have meant that the discussion has at times been more of a shouting match.
Heat pump proponents are fond of pointing out their superior energy efficiency versus hydrogen boilers – between three and six times according to estimates – and often rest their case at that point as if this was the only determining factor.
The main hurdle to the universal adoption of heat pumps, yet one that is regularly overlooked, is the UK’s housing stock. Some 15% of homes in the England were built before 1900, with that figure rising to 23% in Wales. About 46% of English homes were constructed between 1930 and 1982.
Three fifths of homes in England and Wales have low energy ratings, according to the government data.
This indicates approximately 60% of English and Welsh homes are currently unsuitable for heat pumps, which require a well-insulated home to work effectively. However, there is no shortage of unscrupulous vendors who will install one regardless of whether the property is suitable, leading to numerous reports of poor performance.
Heat pumps generally need to sit on the ground outside a property meaning that most flats and many terraced houses can’t accommodate them. Then there is the internal space required for a hot-water tank, something many properties do not have.
There is also the cost of installation. For the 85% of UK homes that use mains natural gas in their property, switching to hydrogen is likely to mean a new boiler, although hydrogen ready boilers that work with both natural gas and H2 will mean it will be negligible switching costs for many. New hydrogen gas hobs and fires will also be needed, and several are already in development.
Purchasing and installing an air source heat pump, by contrast, costs between £7,000 and £14,000 while a ground source heat pump will set you back between £15,000 and £35,000.
For those who put performance over cost, heat pumps will also take longer to heat most houses because of the lower temperature – 65C versus 75C – of the water they send to your radiators compared with a gas boiler. For some homes, this will mean they can’t heat their homes adequately at all and will need to install larger radiators.
A domestic heating system built entirely on heat pumps would have another unintended side effect: the stress they would put on the electricity grid. While natural gas and hydrogen can be stored for use at peak times, electricity needs to be generated almost simultaneously to its use. The UK curtailed a record 2.1 TWh electricity in 2021 at a cost of £507 million. As we build more wind and solar energy capacity this is only going to increase unless we can store the output as clean hydrogen.
Despite all these challenges, heat pumps should still be the system of choice for many existing homes and most new builds. When they are designed into the fabric of a well-insulated home, they are cheaper to run.
For the majority of existing UK homes on the gas grid, a switch to hydrogen provides better performance whilst taking up less space and with a projected lower overall cost. With the UK’s general hydrogen infrastructure continuing to develop at pace hydrogen is the solution for decarbonising those homes for which heat pumps are not a viable option.
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