WHEN it comes to shifting to a zero-carbon society, one of the big things that needs to be had is a public conversation around the way we heat and insulate our homes. It doesn’t sound glamorous. Talking about it doesn’t have the allure of the conversation about the latest breed of electric cars – but we need to do it. We need to talk boilers.

Earlier this year the UK Committee on Climate Change report urged a ban on gas boilers and cookers in 2025, and reported that cuts in greenhouse gas emissions from UK housing had stalled. Heat, meanwhile, accounts for half the energy consumption in Scotland. If we don’t decarbonise heat, we don’t have any chance to decarbonise the whole system.

A big question, then, is what does that mean for the gas boiler? Where do the millions of these across the country fit into a Scotland with a target of zero net carbon by 2045? Eighty per cent of our Scottish homes are heated by gas. The majority of newbuilds are still being constructed with gas boilers. Yet methane gas, a fossil fuel, has no real place in a zero-carbon world. Its burning produces half the amount of carbon dioxide as coal and, when methane leaks, it is a powerful greenhouse gas itself.

This boiler question seems particularly pertinent to me because my own boiler is old, on its last legs, and likely to be up for replacement soon. Yet, when I look around, It’s hard to see what the right replacement technology would be.

Of course, a multitude of new technologies do exist, some of them more tried and tested than others, some of them cheaper, some still just only a few steps beyond speculative. There are air-sourced heat pumps, ground-sourced heat pumps, electric storage heaters, solar heaters, biomass boilers, trials of district heating projects and even the prospect of hydrogen gas in our methane gas grid. It’s hard to see the zero-carbon wood for the trees.

There are two chief stages in the decarbonising of our homes. The first is the kind of energy-efficiency measures, like insulation and double glazing, and this has already been promoted by the Scottish Government for more than 10 years. The second, the shift to zero or low-carbon heating, is a project which, though encouraged through the Renewable Heating Incentive, has only so far penetrated a tiny fraction of households.

Progress has been slow. Dr Niall Kerr, a University of Edinburgh researcher in energy policy effectiveness, believes that for Scotland to have a chance of reaching our zero-carbon targets it is going to require an unseen level of effort.

“The rate of change that we have achieved with government policy in the past few years is of a certain level of magnitude," he says. "We need to move from changing a few people, to changing 10 to 20 times as many people every year.”

Kerr says he has a lot of sympathy for government in this area. “The difficult thing is we’re talking about absolutely everybody. Every single home in Scotland. They all have to change.”

The problem, meanwhile, is that the best way to go about that change seems not yet clear, and not singular. Most experts believe that the answer is likely to lie in a variety of different technologies which will each suit different situations.

As Dr Zhibin Yu, senior lecturer in systems power and energy at the University of Glasgow, puts it: “No single technology will solve this whole issue – because we have different users, different scales, different sources.”

One of the biggest questions is whether the solution lies in a decarbonised electrical supply or decarbonising the gas network. Currently, the most promising answer looks to be electricity, since the technologies are mostly already there – and the chief barrier, beyond cost, is the fact that many homes run on gas appliances which will have to be replaced.

Electricity in Scotland is increasingly being generated by renewables, and by 2032 it’s predicted to be largely decarbonised.

Nevertheless, many still see great potential in hydrogen, particularly given it could provide a solution to the fluctuating nature of renewables, and in a UKCC committee report published last autumn, the gas was touted as part of the answer. This is partly because, in the UK, we have one of the best gas grids in the world. Yu observes: “We’ve got a good gas network, why don’t we decarbonise the gas network? We could potentially switch to hydrogen, either as a percentage of the supply or entire supply after upgrading the networks.”

The problem, however, with hydrogen is that there are still various technical challenges to surmount, as well as financial issues, in that appliances will have to be replaced by new hydrogen-friendly cookers and boilers, which are not yet available.

There is also the issue of how hydrogen is produced. If it’s from methane, then the process involves the production of CO2 which then has to be captured, a process that is still in development and expensive. The other is by electrolysis from water, which is comparatively inefficient.

Meanwhile, low-carbon homes do, of course, already exist. In 2017, 22,000 homes in the UK installed heat pumps – which extract heat from the air, the ground or water. But these technologies are not without their critics.

One issue has been that air-sourced heat pumps have not, for instance, produced as good results here in the UK as they have in some countries. Among the reasons for this has been that the UK has higher humidity levels and in the colder months there is the issue of frost accumulating on the pump as it might on a freezer.

Gillian Stirton is an early adopter of the air-source heat pump and had one installed in 2011 when she and her husband converted an 18th-century derelict house. Her experience, she says, has been overwhelmingly positive. “We decided to go for air source because it was not such a massive amount of infrastructure as something like ground source.”

It was only after they committed to the heat pump that they realised they qualified for a grant for putting it in. “That took some of the sting out of the cost – it was something like 40%. A couple of years after that the domestic renewable heat incentive came in, and again it hadn’t been part of our plan, but we fell on our feet. We qualified for it. It’s not a massive amount – £300 a year – but it takes the sting out of your heating bills.”

They also were able to take advantage of the highest tariff for photovoltaic cells. “Our total energy costs for the year are just under £1,000 and from renewable heating incentive and the tariff we’re getting back certainly more than that – £1,400 a year. But even if you just look at our energy consumption, without those tariffs, the cost for power and energy is remarkable. Even without the incentives I’d do all that again.”

Another zero-carbon possibility is the designing of new homes so well insulated and sealed that they don’t need heating. At the heart of this approach is the passive house movement. John Kinsley is the architect behind Bath Street Collective, a custom-build set of eco-flats designed according to passive house standards, in which his family and three other families live.

“We were keen to make the building as energy efficient as possible and to consider sustainable materials, and attempt to make it fossil fuel free," he says. "We took the decision very early on not to bring gas into the building, even though there is gas in the main road outside.”

The house, since it is airtight and insulated, with mechanical ventilation and heat recovery, doesn’t need heating. It keeps warm just from other appliances, like the fridge, being turned on, and the people within the building. His monthly electricity bill – the sole energy used in the home – is around £60.

This kind of build is something that is already being incorporated into social and affordable housing – Glasgow City Council announced last May that it was committed to delivering many hundreds of social housing units in the city to the passive house standard. Passive house pioneer Gordon Drummond, who recently consulted on five newbuild homes for Shettleston Housing Association, describes the approach as “very much a key way to fight both fuel poverty and climate change”.

This links up to one of the key challenges we face. How to meet our decarbonising targets, and tackle fuel poverty, here in Scotland, where in 2017, nearly one-quarter of all households were estimated to be fuel poor.

As Caroline Rance of Friends Of The Earth Scotland points out: “A large proportion of Scotland’s climate emissions every year come from heating our buildings. Over a million homes are cold and draughty, wasting energy, wasting money and contributing to climate change. Energy-inefficient homes keep more than one in four households in fuel poverty, often forcing people to choose between heating and eating.”

One of the big questions, says Niall Kerr, is: “How you achieve fuel poverty targets, which basically means making energy cheaper for about 30% of the properties, while changing their heating systems and retro-fitting their homes, which is going to cost a hell of a lot of money?” His conclusion is that more public money is going to have to be spent: “Where that comes from is a critical question.”

It’s just one of many big questions on the zero-carbon journey – and Kerr says the public needs to be engaged in them. “We need to have a conversation with the general public that makes them aware of the changes that are coming – like what is already happening in transport – and bring them round to the day-to-day changes that are going to happen, and acknowledge that this is going to cost money.

“If the Government pays for it all then that’s going to have impacts on public services. If private citizens contribute they’re going to have to be happy to do so.”

Gas high efficiency condensing boiler

Cost incl installation: £2000-2500

Cost per kwh: 3.7p

Grants: Available for home owners on benefits replacing old inefficient boilers.

Air-source heat pump

Cost incl installation: £6000-£8000 (Energy Savings Trust)

Cost per kwh: 4.26p

Incentives: Renewable Heat Incentive of £600-£1,297, depending on house size (Which)

Ground source heat pump

Cost incl installation: £10,000 to £18,000 (Energy Savings Trust)

Cost per kwh: 4.26p

Incentives: Renewable Heat Incentive of £1500-£3300 (Which)