Climate Friendly Retrofit Part 4: Decarbonising of our Heating

Josiah Lockhart
7 min readMay 23, 2021

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Decarbonising of heat is one of the biggest issues facing the UK in the next few years as there is already legislation in place that prevents gas connections to new properties in the UK from 2025 and recommendations published this month to extend that to the sale of all gas boilers. Because of that, it is essential that we, as a nation, figure out how to decarbonise our heating stock. It is also important to understand that this needs to be a just transition taking into account the fact that all of the new technologies are expensive and currently cost more to run than gas with gas tariffs averaging around 3p per Kwh and electricity at around 14p.

This has been the least straightforward part of our plans, and something we still have not decided. The set-up in the house is currently a super inefficient outdated gas boiler and hot water tank with no room thermostats consuming around 4612 kWh in a peak month (that is a lot by the way, as the average UK consumption is circa 1000 kWh/mo). Be sure to check out the earlier blogs to understand how this is relevant to the wider project.

Here in the UK, there are several options for moving away from gas as the primary heating system including ground or air source heat pumps, infrared panels, high heat retention radiators, electric radiators, biomass, district heating and even trials in Fife on heating homes with hydrogen. All of these options can be installed in almost any property, but the challenge is finding which one works best in your circumstance. That being said most people exploring this right now should discount the last two as there are only viable in very specific locations as they rely on local infrastructure that only exists in certain places. I’m going to talk through the other options in our current set-up, starting with the most popular.

Heat Pumps are all the rage right now, and in many cases, people will recommend them to you whether or not they are the best technology for your home. This is largely due to both the Scottish and UK governments are pushing and incentivising them hard. In Scotland, HES will give you £10,000 (£2,500 loan + £7,500 grant) if you replace your gas boiler with a heat pump. While ground to water and air to air systems are used across the country, in most circumstances air to water heat pumps is the most relevant for retrofits. If you are unfamiliar with heat pumps, essentially, they take the small amount of heat in the air outside, compress it, and use that heat to heat water or air that circulates through your house. This is similar to how a fridge works, only in reverse. Because the water is heated to a lower temperature than your gas boiler, it runs constantly to maintain a consistent temperature. The low temperature of the water also means it is best suited to underfloor heating, which is more efficient at distributing heat than radiators but can be still be used in radiators. The radiators, however, need to be replaced with special ones that are larger and have more surface area than the ones most of us have in our house. In addition, the plumbing will need to be upgraded in many cases to feed these radiators. From a retrofit perspective, this is the most disruptive option, but it does bring some benefits. The financial incentives can be cheaper to install than other options it also brings a 3–400% efficiency where a gas boiler is closer to 85%. This means that if our home needs 4000kwh of energy to heat the home, it would take 4705 kWh of gas to run a boiler or 1000 kWh of electricity to run a heat pump. But sadly, it’s not as straightforward as that. In most circumstances, Heat Pumps are always on, and because it is low and steady, your home must be well insulated and draught proofed. While it can work in most circumstances, if you are retrofitting and have not dealt with the fabric of your home, it can be a very expensive option to run. Our previous Victorian home was nearly part of the UK government’s “electrification of heat” demonstration group, but at the last minute, just before installation, they deemed our home not suitable for the reasons above. In our current retrofit, we have received advice both in favour of and against a heat pump.

Infrared is the hot new product on the scene. Different to radiators, infrared heats objects in a room instead of the air. If you have ever been to a hot yoga studio, you may have experienced this type of heat. Essentially it heats like the sun. If you have ever touched a south-facing stone wall on a winter day, you’ll understand how this works. This does mean, however, that if anything blocks the infrared panels, the radiation is blocked from the rest of the room. Because of this, the most effective placement is on the ceiling. There are lots of people who rave about this product for its, but because it is new on the scene there haven’t been many studies into it and there equally as many sceptics. In our specific property, this could be a good option as we have quite a few stone walls and a large chimney running down the middle that could be used as a thermal store, already responding very well to thermal radiation from the sun (see the previous blog). But without any government subsidy, a wholesale replacement would cost us just over £16k.

The other, simpler, options are all variations on electric panels or radiators. This technology has been around for a long time. Recently with EU Lot 20 legislation, they have improved. While there have been some efficiency gains over the year, much of these improvements are making the panels “smarter” rather than more efficient. Lot 20 is about encouraging better use with the ability to have WIFI connected, zoned controls with open window detection, and other smart controls. Do not get me wrong, these can make them 30–40% more efficient from an electricity use standpoint. But, what it isn’t is some exciting new technology as those features have been part of other smart heating systems for some time. With electric panels and radiators 1wat of electricity = 1 watt of energy, and the main difference is how long they store the energy once they stop using it. Panels only radiate, radiators hold it for a bit, and storage radiators will keep it warm for an extended period. Like with infrared, there are no government incentives for these (unless you have old storage radiators and are upgrading to “high heat retention” ones), but despite that, it is the cheapest option in our setting coming in at around £4.5k for a full radiator replacement.

None of this directly solves the heating of hot water either, but I’ll dedicate a whole blog to that as we have exciting plans for this that are only a week away, but the summary is that there are pros and cons for each system. And when looking at retrofitting, it is important to consider ALL of the parts of the retrofit together when making a decision. As we progress with our retrofit, the key element is our solar panels and how much excess energy we generate. Using that excess energy efficiently is key, and we have decided to wait until we have enough data before ultimately deciding on a heating system. Our focus is on finding the best system that allows us to dump our excess electricity somewhere to be used for heating when needed. As such, we have ruled out a heat pump due to the size needed to heat our house, the complexity of retrofitting, and the indiscriminate nature of when it uses electricity. Heat pumps can be good for a lot of homes, particularly newer ones with higher levels of insulation, those with smaller footprints, as well as those well suited to underfloor heating. Sadly the issues get more complicated with a retrofit.

For now, the jury is still out for us. We do not have enough data on how our changes to the windows and insulation will affect our demand nor how much electricity we will produce. Later in this series, once our solar array is in and we have started collecting data, I’ll pick this thread back up. We do need to decide before winter comes back around and our indecision on this is delaying other projects including underfloor insulation.

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Josiah Lockhart

Chief Executive at Changeworks