How To Not COP It - Part 3: Low Carbon Heating

This next post in my short series of positive stories on how you can take action and do your bit to be more eco-friendly is about low carbon heating and other measures. Learn how to stay warm for less.

I was recently having a clear out and found an old book, Save The Earth by Jonathon Porritt. Flicking through, a lot of the issues are still very relevant and it could have easily been published this year (with a bit of editing). However, it was actually published 30 years ago in 1991, in time for the Earth Summit in 1992. This was the precursor to COP, of which we are now on the 26ᵗʰ! Will our leaders do better this time or will they fail? It’s time for us all to act.

We have made great progress on acid rain, ozone depletion and phasing out toxic leaded petrol (which was only completed this summer and the lead still remains in our environment). However, we still have a long way to go on other forms of pollution and are in a much worse situation now than if we had acted.

As the famous ancient Chinese proverb goes:

The best time to plant a tree was 20 years ago. The second-best time is now.

We can’t change the past but we can act now.

A big part of the problem is how we warm our homes. While gas boilers are better than the Dickensian practice of burning dirty coal in an open fire they still emit CO₂ and other pollutants. Plus the methane (CH₄) they burn is more potent than CO₂ and the inevitable leaks are problematic. It is clear that we need to immediately stop installing gas boilers in new buildings and replace the ones we have at the end of their useful service with better solutions. However, we need to choose the right solutions that actually solve the problem and don’t create new issues.

What Not To Burn

The proverb above provides insight into why burning wood is no solution. Burning any carbon-based fuel is bad but wood has often been marketed as renewable. Unfortunately it is not carbon-neutral within the timescales that we need, now that we have left things to the last minute. Trees take decades to grow, even if you plant new ones to replace the ones you have burnt then they won’t absorb the carbon quick enough. Planting trees is a fantastic thing to do but we also need to stop burning them.

There are quicker crops (and by-products) but biomass burning doesn’t make sense unless you scrub the exhaust of pollutants (capturing and storing the carbon plus filtering out all of the toxic gases and harmful particulates that damage people’s health). I like the romantic idea of a fire as much as anyone else but you can’t get away from the fact that burning wood in a residential area is irresponsible and discriminatory towards children and vulnerable adults. You see “smokeless” fuels on sale but these are merely lower-smoke and still produce harmful pollutants, many of which stay inside the home. The only true solution is to stop burning stuff. Some small sacrifices are required and we have the technology to do better.

The World Health Organisation says of air quality:

From smog hanging over cities to smoke inside the home, air pollution poses a major threat to health and climate. The combined effects of ambient (outdoor) and household air pollution cause millions of premature deaths every year, largely as a result of increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer and acute respiratory infections.

It is clearly inevitable that motor vehicles will eventually be relegated from their role as ubiquitous tools and replaced by much better electric versions. They will only remain as expensive leisure toys like horses, steam trains and canal or river boats (which can also be electrified). The only question now is; are we nearly there yet?

Will chimneys become architectural curiosities with people wondering what they were once used for? I am confident that if we get through this, future generations will consider our pollution of the gossamer veneer of air that we all breath (and that controls our climate) in the same way that we think of previous generations pouring excrement into the sewer of the street. They both cause disease, are antisocial and stink.

We compost our garden trimmings (and food peeling/scraps) at home in a compost bin at the bottom of the garden and it doesn’t stink. I don’t consider these valuable resources waste as they produce a useful product at the end. This is better than buying compost (peat-free of course). The council also (sometimes) collect garden and food “waste”, a service we use when our bin is full or for the small amount of food scraps that can’t be composted at home. It’s mad to pay for garden trimmings to be trucked away from your home and composted so that you can drive to a garden centre to buy it back. Compost is valuable so it is even crazier to burn biomass on a bonfire in your garden or in a stove inside the home.

There are also virtuous circles and positive feedback loops at play here. You probably realise how a greater number of people walking and cycling creates a friendlier environment for even more people to walk and cycle. You may not have considered that if the air doesn’t smell of smoke then more people will dry their clothes outside, use less energy and make it easier for everyone to run heat pumps. Similarly, now that smoking inside has been banned clothes don’t need washing as much.1

You’ve Got To Pump It Up

In the UK, it looks like heat pumps will be the best technology to replace the primitive technique of simply burning stuff. Our relatively mild climate makes them quite effective but they still work at low temperatures (there is plenty of heat around if you measure in Kelvin). Why set fire to things when we have the technology to capture energy directly from the sun or wind and then use it to extract heat from air?

It is sometimes claimed that because heat pumps run on electricity (which is currently more expensive than gas) that they are far more costly to run. Let’s do some rough estimates and see if this claim holds water (or your coolant of preference).

I am currently being warmed by an air-to-air heat pump with a claimed COP (not that COP, coefficient of performance) of 4.61 according to the data sheet. Let’s round this down to 4. This means that for every kWh of electricity it uses, I get 4 kWh of heat out. This is because it is not simply converting the energy to heat (like a fan or immersion heater) but it is moving it in from elsewhere (in my case from the air outside).

Gas boilers are not 100% efficient (unlike an immersion heater). The Seasonal Efficiency of a Domestic Boiler in the UK (SEDBUK) rating of A-G covers 70-90%. Let’s be incredibly generous and assume a brand new boiler with an efficiency of 95%.

If you pay 4p for a kWh of gas then in our model it costs you 40.95 = 4.21p to get 1 kWh of heat in your house. An old boiler with 70% efficiency might cost you 5.71p/kWh.

So the cost of electricity at which the heat pump becomes cheaper is 4.21×4 = 16.84p. This is more than my peak rate but let’s be generous again and simply assume that a heat pump is roughly the same price to run as a gas boiler at peak electricity prices.

We are on an older fixed rate so if we redo the calculation with the current prices of a variable rate supplier such as bulb (edit: bulb has gone bust) or a variable tariff such as Flexible Octopus then we get a unit price of about 20p. The 5x price differential is not so much down to the market but the government price target cap and many suppliers will charge the maximum allowed of about 4p/kWh for gas and 20p/kWh for electricity (it’s more complicated than this due to standing charges and regions but this is an estimate).

Assuming a 5x price differential and 4x COP then this would mean that a heat pump has similar running costs to a D-rated boiler with 80% efficiency (e.g. one from about 15 years ago). This is not considering the annual inspection and service a boiler requires to stay safe (a heat pump is unlikely to poison you with carbon monoxide if it goes wrong, unlike burning gas or other carbon-based fuels).

However, I don’t run my heat pump on peak electricity. We are on the Octopus Energy “Go” tariff so electricity overnight is only 5p/kWh.2 We also have a couple of solar arrays and a home battery (that charges from the panels and off-peak electricity). The conclusion is that our heat pump is far cheaper to run than our fairly-new gas boiler.

Charges vary by region and you also need to consider the daily standing charge. E.g. the current “Go” tariff has a higher peak rate than ours but lower daily charge. You wouldn’t choose this tariff unless you could shift significant loads to off-peak.

If you are heating a large well-insulated tank of water electrically then you would do it overnight on off-peak energy. I used to live in a property that did exactly this and it had no gas at all. It was built before the fully-Conservative government scrapped the zero carbon homes plan in 2015, a year before it would be completed, following greedy industry lobbying.3

It doesn’t have to be an all or nothing approach. If you are renovating or adding a new room then use a heat pump and use the boiler for the old rooms. It can be done gradually, the same with switching hot water and cooking to electric (maybe just for half the year if you have solar and no storage).

We had a 2.5kW Daikin heat pump installed in our garden office.4 We haven’t had it that long but so far we are very happy with it. It’s quiet, particularly once it has reached the set temperature and is just maintaining it. It can be reached over WiFi to check the temperatures and preheat the room before you need it (although it is very quick to warm up the room anyway). I set the heat pump to 20°C rather than the 18.5°C that the main house thermostat is set at (which is perfectly comfortable) as it can better control the temperature.

As an aside, when I choose any connected tech like this I make sure that there are manual controls first, that the connectivity is just an extra and it works without a data connection. I also prefer devices that work on the local network first and only add an internet connection if you want to control them when you are out. This means things still work when your internet goes down.

It wasn’t cheap (especially now that the government has scrapped the VAT discount on air-to-air pumps) but as it can also cool the air it should be useful in hot summers too and we are likely to get more of them. You are looking at a couple of thousand pounds for a fully-installed heat pump like this but that is not dissimilar to the costs of a boiler (not that anyone should consider gas for a new build).

A whole-house pump will be more expensive but there are £5,000 grants available to help.5 We will certainly be looking into this when it comes time to renovate and replace the boiler we inherited.


As alluded to above we had a garden office built, mostly from wood. Wood is a fantastic material to build with (a much better use than as a fuel). Building with wood locks carbon away into structures. The office has a lot of thermal insulation boards incorporated so that it maintains its temperature well.

Insulation is very important (see my previous post) and it is one of the first things you should do but it is also independent of the heat source you use. It is a good idea no matter if you are using a boiler, fan heater or heat pump.

We are still in the early stages of our journey and have lots of future plans. These include recovering heat from exhaust air and used water (e.g. from showers). These are not waste as they still have lots of useful resources that can be extracted and reused.

In the next post I’ll cover some other miscellaneous eco actions that we have taken (and you can too).

  1. If you are a cancer-stick addict then please at least be considerate of other’s health and don’t tar your lungs right outside the entrances of buildings. Other countries have a minimum distance smokers can be from doors or windows and I would love that to be adopted here.
  2. If you would like to do your bit by switching to 100% green electricity and get £50 credit from Octopus Energy then you can use our referral link. It might even be cheaper than your current supplier.
  3. Housebuilders, planners and green groups have condemned the government for scrapping plans to make all new UK homes carbon neutral.
  4. 2.5kW is a peak rating, the heat pump doesn’t use anywhere near this much power most of the time. It is typically using only a few hundred watts.
  5. Ministers have unveiled plans for £5,000 grants to allow people to install home heat pumps and other low-carbon boiler replacements as part of a wider heat and buildings strategy that some campaigners warned lacked sufficient ambition and funding.

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