Electricity and heating

1 Whole houses
2 Centralised systems
3 Broader interpretations
4 Localised needs
5 Efficiency in timing
6 Conclusion
7 Related articles on Designing Buildings

[edit] Whole houses

Firstly, from the get-go, and so it is clear, I am an advocate for heat pumps. I am also an avid, probably more so, strong supporter of the strict Passivhaus approach as the most logical approach to new builds. And I see the Passivhaus EnerPHit standard being very suitable for many retrofit projects.

In terms of the latter, MVHR is carefully aligned with high-level fabric improvements, which means that what is asked of any heating system is dramatically reduced. To my mind, and secondary to this, it is the holistic entirety of the fabric performance that is key, and this whole house system (whole house MVHR) will be the nearest one can get to the feel and functionality of what used to be a centrally heated system but one that doesn't rely on burning cheap gas.

Furthermore, there isn't much give in terms of how much that entire building fabric needs to be improved to achieve the Passivhaus standard, so any heating requirements (or indeed cooling requirements in hotter climates) are minimised by those fabric performance uplifts.

In terms of the former, one could argue that the same applies; that is to say, it is only with dramatic fabric performance improvements, despite the super coefficient of performance (COP) from most heat pumps, that they are a perfect solution to electrified heat. So reduce the need and, in turn, reduce the required running temperatures, as opposed to the higher temperatures achieved from burning stuff, and all will be good.

There is, though, a but in there, or maybe even two. Without the possibility of running at lower temperatures (as a result of fabric improvements), the same 'feeling' that we are used to from central heating could be more costly than expected, and secondly, whilst heat pumps cycle, there is generally the necessity for them to essentially remain on. Balancing these factors is most clearly explained in the document covering heat pumps in retrofit, 'The Right Time for Heat Pumps. Decarbonising home heating in a staged retrofit', published by the UK Passivhaus Trust in April 2024.

[edit] Centralised systems

Gas was first used in the UK as early as the 1800s for gas stoves and lighting, but it wasn't until the 1970s and 1980s, driven by the discovery of North Sea gas and government-led programmes, that gas for heating, in particular central heating systems, became more widespread. These gas-driven, centralised wet radiator heating systems are possibly still the most common form of heating in the UK and typically have running flow temperatures of 70-80°C.

Heat pumps at their most efficient generally run at lower temperatures of 35-55°C, some 25-35°C lower. It is this temperature difference that impacts not only the speed of heating but also the overall comfort of the system and why the use of heat pumps needs to be treated as a whole package. There is, however, in some areas still a continued sense that it is ok to just swap out a gas boiler for a heat pump and that same comfort warmth that we became so used to with central heating will be achieved; to my mind it won't.

I have and continue to hear unfortunate heat pump tales of woe, that costs are dramatically higher or that the new system just doesn't work, and whilst I don't know enough about the projects, my guess is it is related to running temperatures, the need for them to be constantly on, user expectations and how they use the controls. It still surprises me the number of people who see heat pumps as simply a one in, one out replacement for a gas boiler, and many risks exist in that. The danger being that the technology, as a result, gets a bad reputation from the instances where it fails or is perceived to have failed.

It has always seemed to me that there are other more localised advantages to fabric improvement which are often overlooked. For example, where the internal surface temperatures between wall and window in the case of triple glazing do not vary as much as with standard double glazing. It is, in terms of comfort, often the temperature differences that the body notices, and merely levelling off those differences by reducing radiant coolth from windows can also help improve comfort without necessarily increasing room temperature.

[edit] Broader interpretations

So my point here is there should perhaps be a widening of what we consider to be a heating system. For instance, Mechanical Ventilation Heat Recovery (MVHR), with its ability to recycle and preheat air, should be considered alongside heat pumps and other systems as a form of heating system.

The differences are the nature of combustion, wet versus dry systems (in this case, ventilation), and the fabric. And the similarity is that both the correct approach to the installation of heat pumps (alongside fabric upgrades) and the Passivhaus approach looks towards whole-house solutions, both in terms of the fabric and technology. The result is the potential to achieve comfort which is in line with centralised heating of the past, albeit without the burning of gas. But is there also perhaps some value in re-examining alternatives to whole-house systems, be that in terms of fabric performance and technologies?

Electrical heating systems, since the introduction of cheaper gas, have generally been considered the more expensive option when it comes to both space and water heating. But technology has moved on; there are numerous heating systems on the market that might now be brought into the race rather than seeing heat pumps as a one-horse race (especially if poorly installed). This was highlighted in the recent report “What should I do?” Accelerating Heat Electrification by providing customer choice, published by BEAMA, which runs through the market potential of electric heating technologies, starting with the focus on air source heat pumps but going on to describe domestic hot water heat pumps, electric panel heaters, electric radiators, electric underfloor heating, modern high heat retention (HHR) storage heating systems, phase-change heat batteries, smart heat batteries, and smart hot water cylinders.

[edit] Localised needs

I would argue that we don't need to stop there, and there is potentially a place, in certain circumstances, for the wide variety of other heating types, designs, locations and so on when we look at localised heating solutions. Furthermore, whilst the focus is often on Passivhaus and whole-house mechanical heat recovery systems, localised ventilation systems may also be part of the solution, such as dual-flow or single-sided heat recovery systems. Especially given the context that most houses are required in the building regulations to install, for example, extractor fans in bath and shower rooms, many of which extract heat as well as stale air, heat which could potentially be exchanged and retained.

Prior to the uptake of gas central heating systems, the nature of heating, as well as house planning, was more localised; for example, the kitchen would be heated when in use, the living room heated the same, and importantly with doors between. Would open-plan living have been possible without gas central heating? Is there a case to move back (just a little) to sensibly dividing homes, be that by drapes, curtains or doors, and might more localised heating systems also have a part to play in the electrification revolution?

The use of electricity and heating systems shouldn't be just about direct heating systems or even just about heat pumps but should include the wide range of types, locations, shapes and sizes of how and particularly when electricity might be used to create heat. It includes its indirect use as well in the transfer of heat and preheating, taking a broader view to include indirect heating, heat transfer, heat storage, heat pumping and heat conversion, but also solar solutions that might rely on electrical pump systems. Consideration of both water and space heating solutions, which have very different requirements, but there is perhaps the need to reiterate that many of these solutions need a different understanding from us compared to what centrally heated users have been used to.

[edit] Efficiency in timing

Homes, often in remote locations, that were never connected to the gas grid have been forced to continue using electricity for space and water heating, often topped up by wood or coal. In general, typical homes in these areas would have (and often still do) used night storage heaters for space heating and immersion heaters for water heating.

The benefits of night storage or economy-seven heating still exist and, economically, at least in some cases, can balance out some of the efficiency benefits of heat pump systems, which, although three times more efficient, may be using daytime electricity at three times the price. As well as the aforementioned need for heat pumps to effectively stay on, whereas night storage systems are intermittent systems. Plus, the nature of wet versus dry, for example, in older buildings can potentially come with associated risks or at least complications.

Many of these technologies' direct, intermittent and localised systems have improved with efficiency and design over time, such as HHR heaters over standard night storage heaters. Immersion heaters that can store heated water for much longer also benefit from reduced night rates and even have integrated tank heat pumps included. Agreed, many of these systems cannot compete in a race with the feel of gas central heating or the comfort in a Passivhaus, some providing background heating that needs perhaps localised top-ups. But they should be considered in the discussions about electrification of existing homes and perhaps at the moment at least in terms of support funding. they don't feel like they are.

[edit] Conclusion

In summary, whilst Passivhaus or significant fabric improvements and air source heat pumps might remain front runners, like the hare and the tortoise, there are many different heating animals in the race, running in different ways. Perhaps thinking differently about where we heat as well as how we heat can help more people step away from gas, especially in circumstances where the front runners are out of reach, so that the finish line is still crossed even if in a different way.

And finally it does sometimes feel that there is a tendency to use the same thinking that was adopted with the introduction of gas and central heating. That is that there is one solution per household, it was gas and now it is heat pumps, but in truth there is sense in looking at more than one system. For example if a system functions at its best for the majority of the year don't try to make it work for all of the year, just use a system, perhaps intermittent and local like a direct heater or dare I say it a wood burner for those few days. Importantly from a grant perspective and encouraging users to adopt new technology, smaller steps might work better than all or nothings.