Are Scotland's heat pump plans threatening to boil over?

The Scottish government is launching a consultation on plans to downgrade the energy efficiency ratings of homes with gas boilers.

It is part of a strategy aimed at removing fossil fuels from heating in more than one million homes by 2030, a key milestone on the journey to reach a headline net-zero target by 2045.

Zero Carbon Buildings Minister Patrick Harvie argues the change would accelerate the uptake of more environmentally-friendly central heating systems such as heat pumps.

But others question their suitability for many Scottish properties, and warn that homeowners could be landed with huge costs.

The Scottish government estimates about 20% of Scotland's carbon emissions come from heating buildings.

Mr Harvie wants to revamp the Energy Performance Certificate (EPC) ratings, meaning homes with gas boilers would be downgraded compared to those with climate-friendly systems such as heat pumps.

The government has pledged that all residential homes will meet band C in energy performance certificate standards by 2033, "where technically and legally feasible and cost-effective".

Such requirements could potentially be enforced at certain trigger points, such as when houses are bought and sold, but the government is yet to set out the legal framework for its rules.

Ministers have launched a consultation on proposals to reform EPC ratings and draft legislation for the Heat in Buildings Bill is yet to be published.

Under current legislation, gas boilers will be banned from new-build homes and other buildings seeking a building warrant from next April.

The Scottish Conservatives said Mr Harvie's plans would be "deeply concerning" for homeowners with gas boilers.

The UK government has set a target of 600,000 heat pump installations per year by 2028 and said sales of gas boilers would be banned from 2035.

But currently fewer than 50,000 heat pumps are fitted in British homes annually and the UK is bottom of the heat pump installation league table in Europe.

According to Scottish government statistics from 2021, only about 11% of households - approximately 278,000 - have a renewable or very low emissions heating systems, such as a heat pump, biomass boiler or electric storage heating.

Heat pumps are favoured by ministers because they are extremely efficient - producing up to three units of heat for every unit of energy put in to the system.

A heat pump is an electrically-powered device that absorbs heat from the air, ground or water around a building.

For example, air-source pumps suck in outdoor air and pass it over tubes containing refrigerant fluids to extract the heat.

Typically, it costs about £10,000 to buy and install a heat pump although that can vary depending on the property.

To tackle the costs, the Scottish government currently offers a grant of £7,500 towards the cost of a heat pump, plus interest-free loans to cover the remainder of the installation.

This is higher than a £5,000 grant offered in England, Wales and Northern Ireland.

A World Wildlife Fund (WWF) report published earlier this year said most households with oil or electric heating would see significant falls in energy bills with a switch to heat pumps.

But the cost implications for homes with gas boilers are less clear. Although heat pumps are efficient in how they draw heat from the atmosphere, they themselves are powered by electricity which is currently three times more expensive than gas.

Heat pumps are also not considered suitable for tenement buildings - which Scottish government research published this year estimates make up 40% of Scottish housing stock.

A government working group is currently coming up with alternative proposals for such properties.

Heat pumps produce hot water at lower temperatures than gas boilers, meaning homes may require larger radiators and microbore piping will have to be removed.

They work best in homes with high levels of insulation.

So further costs may come, in the form of work to add insulation or double-glazing to homes, to make the systems more effective.

Alternative electric heating systems include immersion boilers, electric fires, fan heaters and infra-red radiators, for example, but none are considered as efficient as heat pumps.

Hydrogen-powered boilers are another option.

They work similarly to gas boilers, except they burn hydrogen instead of natural gas, meaning there would be no need to replace radiators.

However, processes for extracting and producing hydrogen are not as well developed as other fuels and could prove to be less efficient than using electric heat pumps.

The Scottish government's plans are being spearheaded by Mr Harvie after the Greens entered government under the power-sharing Bute House Agreement in 2021.

Since then, two key Green policies - Highly Protected Marine Areas and the deposit-return scheme - have been shelved following dissention at Holyrood and objections from Westminster.

This has contributed to unease about the power-sharing relationship within SNP ranks. In the leadership contest to replace Nicola Sturgeon in early 2023, only eventual winner Humza Yousaf committed to upholding the Bute House Agreement.

Ministers will be eager to avoid any further controversy about Green-led policies, but concerns were raised by opposition figures following Mr Harvie's announcement about EPC ratings.

Scottish Tory net zero spokesman, Douglas Lumsden, said the proposals were "hugely naïve" as he accused Mr Harvie of "typically acting like he knows best by ploughing ahead with these plans".

Labour peer and businessman Lord Haughey, whose company is one of Scotland's leading suppliers of heat pumps, told BBC Radio's Good Morning Scotland that electric boilers would be more cost-effective and environmentally-friendly options for most Scottish homes.

He also said heat pumps do not work as efficiently in Scotland as they do in other countries, with some liable to malfunction at temperatures of minus 5C (23F) or lower.

Mr Harvie responded by arguing that European countries where heat pumps are more common, such as Norway, Sweden and Finland, also have some of the coldest winters.

"It's going to take us to 2045 to decarbonise our buildings, but we're starting now and we need to accelerate," the green minister said.

"So this is not far-off, futuristic technology - heat pumps are a very well tried-and-tested technology."

He told the BBC that companies were investing in smaller, more efficient heat pumps, adding: "That's where the innovation is going. That's where the industry is going."

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