Patrick Harvie today launched his consultation on draft heat in buildings legislation, which will bring Scottish homes and buildings into a wider plan in Scotland’s push to Net Zero.

Under the Minister for Zero Carbon Buildings, Active Travel and Tenants' Rights’ plans, all homes will need to end their use of fossil fuel emission heating systems by 2045, when Scotland will become net zero in law.

The Green co-leader’s blueprint aims to give “households the information they need to plan” and “businesses the confidence to invest” during the transition period and beyond.

Today’s announcement set a new target, that by 2038 all public buildings will be required to have clean heating systems, although the minister insisted that no requirement will be made of home-owners or businesses until at least 2028.

Heat pumps form a key part of the policy and in recent months detractors and advocates have emerged to express their opposition or provide a glowing reference.

Here the Herald’s Rebecca McQuillan reflects on her own experience and writes about what she learned from having a heat pump installed in her home:

There’s an awful lot said and written about heat pumps. Some of it is sensible comment; some of it unfortunately isn’t. But while there’s a debate to be had about how to decarbonise heating in homes effectively and affordably, and while heat pumps aren’t suitable for every property, they will, as Patrick Harvie made clear writing in this newspaper recently, be an important part of the future mix.

So how good are they in practice?

Before we installed a heat pump in our home, I was supportive of the idea in theory, but had some niggling doubts. We were replacing a gas boiler with an air source heat pump and I was worried that it wouldn’t work very well as our 60-year-old home had radiators, not underfloor heating (which is generally seen as the ideal way to distribute heat from a heat pump). I also worried that we didn’t have enough insulation.

(You might wonder why we did it if we had these concerns. Well, we wanted to cut our carbon emissions, there were – still are – good grants and loans available, and we hoped to save money on our heating bills.) I spoke to three separate lots of people who already had heat pumps, two of them found through Home Energy Scotland (HES). They were reassuring and seemed puzzled by some of my questions about what was, to them, as conventional a heating system as a gas boiler.

But I still worried the place wouldn’t be warm enough. Heat pumps heat water to a lower temperature (around 50 degree Celsius) than gas boilers (at about 60-65 Celsius). So we bought a standalone convector heater on the assumption that our radiators wouldn’t keep the place toasty on some winter days.

Eighteen months on, I look back with a degree of bemusement at my anxiety. The heat pump has been great. When I hear people talk about them as if they’re dodgy technology, I just don’t recognise what they’re on about and wonder where they are getting their information. Yes, it does work. No, we never needed the convector heater. And yes, we have saved money on our heating bills.

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We have saved money on our energy bills

I became a spreadsheet nerd in the first year of our heat pump, comparing our energy usage to the year before. The weather conditions across the two years weren’t markedly different.

We saved around 18 per cent on our energy bills in the first year compared to what we would have spent the previous year if energy had been at the same prices. We had cavity wall insulation installed about three months before getting the heat pump so that will account for a bit of the saving.

Heat pumps in Scotland typically cost £7000-£13,000 to put in, according to HES. HES provides a grant of £7,500 (£9,000 in rural areas) and an interest-free loan of up to £7,500 on top of that. For some people, installing a heat pump will cost around the same as replacing a gas boiler. For larger heat pumps, there will be a longer period of loan payback, hopefully offset by bill savings.

The Herald:

Our cavity wall insulation was enough

Obviously regardless of how you heat your home, the more insulation the better as it helps keep heat inside so your appliance has to work less hard and your bills are lower. Because they operate at a lower temperature than gas systems, though, insulation is even more important with heat pumps. We worried cavity wall insulation wouldn’t be enough but it’s been just fine (grants are available for insulation too, it should be said). We plan to add more insulation in time anyway, but the cavity wall fill is doing the job.

The house is warm enough, even in winter

We set our thermostat to 20 degrees, as before, and the heat pump works efficiently at that level.

Heat pumps are attached to the outside of homes, or to nearby walls, and draw in air from outside. The heat is then removed from the air (this works even on cold days) and put through a compressor to raise the temperature. That heat is then used to warm water for the taps and radiators.

I imagined the water would feel tepid. Daft, really: I should have realised that because 50 degrees is much higher than body temperature, it would be hot to the touch. I was nerdishly thrilled to find we could dry clothes on our radiators just like before.

They’re not noisy

The fan in the heat pump draws in air on one side and expels cold air from the other. I had visions of the neighbours objecting to the hum, but I’m not sure they even realise it’s there. Some models are apparently quieter than others, but you have to be within two or three metres of ours (a Grant Aerona) to detect it. Plus it’s off a lot: it’s thermostatically controlled and goes off when the house is warm enough.

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You need them sized correctly

This point was stressed to us both by Home Energy Scotland and our heating engineer. You want a heat pump that’s sized “just right” – too small and it will have to work too hard; too big and it will be powering up and down too much. Neither is ideal for your heating bills.

Ours must have been sized correctly because for every unit of electricity we put into it, we’ve been getting more than 4.5 units of heat out on average (called the coefficient of performance) – we’re told this is good even for an air source heat pump.

Heat pumps provide a decent hot bath

We were sceptical that an air source heat pump could warm the water enough for a proper hot bath. Well, it does. Even my heat-worshipping husband has to add cold water before he can get in.

Ground source vs air source?

Ground source heat pumps are sometimes held up as the ideal because they are even more efficient than air source heat pumps. But it quickly became clear a GSHP would have cost loads more, required drilling rigs and 150m boreholes, and we’d have been liable for the cost of removing the grit and mud dug up. Air source shouldn’t be seen as second best.