Patrick Harvie’s strategy to replace thousands of gas boilers with heat pumps is under growing pressure after statistics revealed progress in meeting renewable heat targets is "some way off track".

The Green minister for zero carbon buildings is aiming to clean up how one million Scottish homes are heated by 2030 - with the Scottish Government’s preferred option to scale up the number of heat pumps, run off renewable electricity, being installed.

But the Scottish Government remains significantly behind a target due to be met in 2020 for 11% of homes to have renewable heating systems installed – with the initial target due to double to 22% by 2030.

Read more: Gas boilers set to be penalised under energy efficiency overhaul

Data for 2020 shows that only 6.4% of homes in Scotland had renewable heating systems against the Scottish Government target of 11%.

Mr Harvie is currently “considering alternative approaches and metrics” to measure success amid the lack of progress and “will publish an updated target for renewable heat” later this year.

But the Scottish Government has admitted that there “is much more to be done” to scale up progress.

In the latest monitoring report of the Scottish Government’s climate change plan, analysis found that the emissions of buildings has exceeded its targeted pollution by 0.7Mt of carbon dioxide.

Despite statistics being available up until 2020, the latest Scottish Government report indicates it is “too early to say” what the percentage of homes powered by renewable heating systems is. But it is clear that not enough progress has been made.

Read more: Harvie calls for UK action so heat pumps lead to lower energy bills

As part of efforts to keep legal climate targets on track, the Scottish Government committed that “zero emissions heat installations we will need to scale up to provide a total of at least 124,000 systems installed between 2021 and 2026 and peak at over 200,000 new systems per annum in the late-2020s”.

But figures for the installations of heat pumps by the Microgeneration Certification Scheme (MCS), the most common form of renewable heating system, shows that only a fraction of the progress required has been achieved.

In 2020, only 2,440 MCS-certified heat pumps were installed in homes in Scotland, 4,242 in 2021 and 4,712 in 2022.

According to data, £14.3m was handed out to households to install heat pumps in the 2022-23 financial year as part of the Scottish Government’s Home Energy Scotland grant scheme – covering air source heat pumps, ground source heat pumps and water source heat pumps.

The statistics show that only 2,052 air source heat pumps received grant funding in the last financial year, 58 ground source heat pumps received Scottish Government grants and only one water source heat pump was installed with public grant funding.

The Scottish Government said it does not hold information on the proportion of replacement heating systems installed which are zero direct emissions.

Read more: Patrick Harvie cuts funding for solar to push heat pumps strategy

Scottish Conservative MSP Liam Kerr, said: “Patrick Harvie’s rhetoric around heat pumps simply doesn’t meet with reality.

“Most people recognise that heat pumps could play a crucial role in achieving net zero targets, but the Green minister’s dogmatic approach is the wrong way to go about meeting them.

“If he is going to remain inflexible, then he has serious questions to answer over how he will reach targets which are still some way off track.”

The Herald: Liam KerrLiam Kerr

He added: “The SNP-Green government seems wedded to a one-size fits all approach in replacing gas boilers, while delivering a pitiful amount of funding so far to support hard-pressed householders.

“Their plans won’t work for householders, and they won’t work for the environment.”

Mr Harvie has admitted that low temperature air source heat pumps are “deemed to be technically suitable for around 55% to 76% of homes currently existing in Scotland”.

He added: “If homes were to adopt measures to achieve Energy Performance Certificate (EPC) C where technically feasible and cost-effective, then this share would increase to 75% to 77%.”

Mr Harvie stressed that “electric storage heaters are found to be suitable for 82% to 100% of homes before energy efficiency measures are installed, and 95 to 100% after”.

Read more: Patrick Harvie says 100k heat pumps a year will revive climate target

But concerns have been raised over some families being left behind if their homes cannot be converted to a suitable low-carbon heating system.

Scottish Labour MSP Richard Leonard, said: "Yet again, the SNP-Greens' delivery falls a long way short of their rhetoric.

“It is no good talking about a just transition to a greener economy, we need to invest in it to tackle the twin crises of the climate emergency and soaring cost of living."

A Scottish Government spokesperson said: “More than 4,700 MCS-accredited heat pumps were installed in domestic properties in Scotland in the 2022 calendar year.

“The Scottish Government funds climate-friendly heating systems through a wide range of programmes in addition to the Home Energy Scotland scheme including area-based schemes, Warmer Homes Scotland, the social housing net zero fund and the heat network fund.

Read more: Patrick Harvie: Why we need to change the way we heat our homes

“These schemes have supported take-up of heat pumps and other climate-friendly alternatives.

“As well as supporting individual homeowners, we provide SMEs, the public sector and the social housing sector with targeted support, as part of the £1.8bn allocated over the course of this parliament to support heat decarbonisation and energy efficiency, and we are seeing increasing demand across all our funding streams.

“We have made good progress in recent years, but realise that there is much more to be done.

“Our Heat in Buildings Strategy sets out our plan to transform Scotland’s homes and workplaces over the next 24 years – phasing out fossil fuel heat and improving energy efficiency so that our buildings are warmer, greener and more efficient.

“Later this year we will consult on proposals that could inform a Heat in Buildings Bill, and our developing plans for regulation to deliver and accelerate the switch to low and zero carbon heating systems.”