The UK aims to phase out the installation of new and replacement domestic gas boilers by 2035 as part of its 2050 net-zero strategy. But the low-carbon alternatives, such as electric heat pumps, have their own cost and feasibility challenges that could limit the UK’s decarbonisation of heating this decade.

The government’s Heating and Buildings Strategy sets an ambition to install 600,000 heat pumps a year by 2028, up from the current annual rate of about 35,000. To date, 265,000 heat pumps have been installed—accounting for less than 1pc of the country’s total heat capacity.

The UK has lagged behind mainland Europe in heat pump installations in part due to its historic dependence on North Sea gas and extensive investment in gas infrastructure. In contrast, European nations such as France—where nuclear energy is dominant—have seen higher gas prices compared with electricity, pushing households toward electric heating.

The government plans to provide grants of £5,000 ($6,700) from April this year to encourage homeowners to install low-carbon heating systems. But this may not be enough to cover the full cost of installation.

While replacement gas boilers cost roughly £2,500 to install, heat pumps can cost £8,900-14,500, according to Martyn Bridges, director of technical communication and product management at boiler and heat pump manufacturer Worcester Bosch.

£5,000 – Government grant for low-carbon heating

The UK currently has 17mn homes using combination boilers, which heat water directly without requiring a hot water storage tank. Retrofitting a heat pump therefore requires additional work to install a new hot water tank. “Most boiler exchanges can be done in a day or a day-and-a-half. Depending on the amount of remedial work, a heat pump would be double that,” says Bridges.

And while the government intends for heat pump costs to fall by 25-50pc by 2025 as demand scales up, Bridges argues the cost of production has already been optimised to meet the scale of demand in Europe. “We do not see us being able to take 50pc out of the price of a heat pump that we sell. You might get 1-2pc.”

Heat pump production costs are likely to increase due to rising raw material costs, Bridges adds.

Heat pumps also face additional costs during operation. Domestic electricity costs 18.32p/kWh, while gas costs 4.6p/kWh, both of which are expected to increase due to the current wholesale gas price spike.  However, the balance could be tipped to favour electricity over gas if stricter carbon prices are set.

Hydrogen not ready

Hydrogen for use in heating is unlikely to be feasible before 2030 due to several factors, says a recent paper by university Imperial College London.

Low-carbon hydrogen supply is extremely limited. Although the UK could have 5GW of low-carbon hydrogen capacity in place by 2030, hard-to-decarbonise industrial uses are likely to take priority over domestic heating.

Even with sufficient supply, hydrogen will require infrastructure retrofits, the paper says. The UK’s distribution and service pipelines, which feed gas from the grid into homes, are either made from polyethylene or are due to be replaced with the plastic by 2032. But the high pressures of hydrogen gas cause steel transmission pipelines to become brittle and increase the risk of damage, meaning 100pc of the current transmission pipe network needs to be replaced.

And while most appliances manufactured since the mid-1990s are able to run on a 23pc hydrogen blend, they will need to be adapted or replaced to run on pure hydrogen. The H21 project run in 2016 found that, even with mass manufacturing of hydrogen appliances, the effort to make pipework, boilers and appliances safe for running on hydrogen would cost £3,078 per property.

The relative carbon intensity of hydrogen compared with heat pumps may also limit its rollout.

£3,078 – Cost per household for hydrogen retrofit

Air- and ground-source heat pumps respectively produce 0.11kg and 0.1kg CO₂e/kWh of thermal energy due to the UK’s gas-dominated electricity generation. Natural gas boilers are more than twice as carbon intensive, at 0.24 kg CO₂e/kWh thermal energy.

While the direct carbon intensity of hydrogen boiler thermal generation has yet to be determined, production of the fuel alone can be carbon intensive depending on source. A kilogram of green hydrogen produced by wind-driven electrolysis is estimated to produce 0.97-2.21kg CO₂e. Blue hydrogen is estimated to produce 3.4kg CO₂e/kg, while grey hydrogen produces 8.9-12.9 kg CO₂e/kg.

Low pressure

While these debates rage in industry and academia, the public is largely unaware of the scale of change necessary to decarbonise household heating. According to surveys performed by government research centre Energy Systems Catapult, while 65pc of respondents said climate change was a “very serious” problem, less than half agreed that switching to a heat pump or hydrogen boiler would reduce their personal impact on climate change. And less than a fifth said they were likely to move to a low-carbon heating system when replacing their current boiler.

“We tend to run boilers to destruction,” Bridges says, noting most customers will replace a boiler only if their existing one is irreparable, unreliable or impossible to buy spares for.

Only 19pc of the public would consider replacing a working heating system with a low-carbon option, according to a survey by the UK’s Department for Business, Energy and Industrial Strategy.

The Imperial College London paper notes that households are likely to prefer hydrogen boilers due to familiarity with their existing systems.

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Author: Polly Martin