As we enter a cold snap, and energy prices have risen again, we are more worried about how to manage our home heating. The easiest way to reduce bills is to turn down the thermostat. Do we really need 20°C or higher at home? Perhaps this is merely a social convention. David MacKay published ‘Sustainable Energy Without the Hot Air’ in 2009, in which he proposed turning down the thermostat at home to 16°C to reduce carbon emissions. At his publicity talks he explained how his household (with wife and two children) had successfully adapted to these conditions. He also incorporated the 16°C target in the 2050 calculator for scenario planning for net zero. This was the extreme level for one of the home energy 'levers'.
I find this idea scary; thick jumpers do not seem to keep my hands warm – even at 19°C I find my fingers stiffen so that I struggle to type unless I wear half-fingered gloves. I know many people are forced to endure such conditions through fuel poverty but I cannot imagine doing it from choice. Is this reasonable?
So I was intrigued to read about a group of 23 people in Belgium who decided to experiment with heating at home – can they turn down the setpoint on the thermostat and heat the body instead, generating less carbon emissions while still enjoying their living conditions and avoiding any ill effects? [1].
By the third season some were comfortable with the mean living room temperature as low as 14°C.
Strengths and weaknesses in the research.
There are lots of weaknesses in this research – the small number of participants for one (23) and the lack of a well-established baseline for another. Also, although they agreed this experiment was not a ‘race to the coldest’ it is hard not to imagine some competition within the group, reporting to each other monthly. On the other hand there were lots of strengths too. They logged temperature in the living room as a measure of thermal comfort and heating demand. The participants were diverse: almost half were women (11/23); there was a large age range (20s to 60s), different types of home (apartments, terraced and detached) and EPC grade (B to G). They ‘co-designed’ the experiment and supported each other throughout. By conducting the project over three winters they measured long term effects.
I won’t go into all the details, but here are some insights.
They adapted their clothing rather than using personal heating devices.
The group made rules which allowed the use of personal or local heating devices such as heated blankets, and chairs, radiant panels (especially for a quick boost) and even standalone heaters in the room. In the end these were used sparingly, and they relied mainly on extra clothing. When sitting down they used blankets. However, the availability of the active heating devices was important as it relieved the fear of being cold. (David MacKay’s household had a similar rule, whereby if anyone was cold despite warm clothing they would put the central heating on boost for an hour.)
They made different choices in their clothing. They wore thermal underwear and they enjoyed ponchos on top of jumpers; they liked clothes with a hood to cover their heads. Sometimes they wore caps or gloves indoors. Some of them installed heavy curtains in the home to minimise draughts. Draughts can make a big difference to perceived temperature and you can use them for partitions or for hiding a cold wall.
Energy prices increased during the project
Electricity usage did not increase, despite the use of electric heat for blankets etc. This was probably due to rising price, as the second and third seasons overlapped with the war on Ukraine that massively disrupted energy supplies. Doubtless the high price was an added incentive to reduce gas and electricity consumption, though at the start of the experiment the main motivation for most of the participants was environmental benefit.
Acquiring the ability to adapt takes time
As the project progressed they drastically changed their attitude to thermal comfort. For most, prior to the project the extent of their interaction with the heating system was to switch it off in spring and on in autumn. They associated cold with poverty, discomfort and even illness. By the end, they regarded cold as invigorating and said warmth made them sleepy or heavy. They enjoyed the sense that their body adapted to different temperatures and they would make conscious decisions on clothing to wear, and other measures for keeping warm instead of assuming the home would be warm enough with their usual clothes. This process of adaption and learning took time – weeks or even months.
Breaking social norms is difficult.
They found it hard to explain their choice to friends and visitors. They were careful to frame the project in a positive way – as exploring the idea and practicality of heating the body rather than the whole home. Sometimes they temporarily increased the setpoint for visitors, or they offered heated blankets and other devices for the guests to try. Some of the group found this the biggest barrier – breaking the social norms was a major difficulty.
Cold can be bad for the fabric of the home.
Comfort was not the only limiting factor. Drying clothes became more difficult (dehumidifiers are a good solution) and two homes developed mould, one on a poorly ventilated surface and one on a badly insulated wall junction. After that they all acquired humidity sensors and took more care monitoring conditions. To decrease humidity you can increase ventilation (up to a point) or increase the heating. Both increase energy use: see How Warm Should Your House Be?
What temperature is considered adequate for health?
In the days before central heating our homes were colder on average. However there was usually at least one room kept warm, often just as warm as today [2]. (As I recall, we did our homework in the warm room not in the chilly bedroom.)
Cold homes are associated with poor health. In one UK study of 8000 homes, 16% were found to be 'cold' where this is defined as less than 18°C. Those who resided in cold homes had higher blood pressure readings, worse handgrip, lower vitamin D levels, higher cholesterol levels, ..., lower level of white blood cell count and worse lung conditions [3].
Public Health England conducted a literature review in 2014 and concluded The currently available evidence base, alongside expert discussion, suggests that heating homes to at least 18°C poses minimal risk to the health of a sedentary person, wearing suitable clothing. At below 18°C, negative health effects may occur, such as increases in blood pressure and the risk of blood clots which can lead to strokes and heart attacks. .... Younger healthy adults may find it easier to increase activity levels and adjust their clothing to keep warm, ... [4]
These risks sound scary, but the guidance assumes central heating and does not allow for personal heating devices such as heated chairs and blankets.
Is it worth it?
Central heating has made us rather lazy in terms of adapting to different temperatures. This experiment shows that, for healthy people, heating the home to 16 °C or even lower, combined with suitable clothing and personal heating devices, is both practical and enjoyable, or at least not unpleasant. However over 65s and other vulnerable adults may not feel cold even when they are suffering ill effects. Also, it takes conscious effort and determination to adapt and it is hard to break today’s social norms. Is it worth it?
Reducing the thermostat can make large savings on heating bills – perhaps up to 50% – but this research was not able to measure it. The best savings were made in an apartment that reduced heating energy by 98% but this involved special circumstances. This home (an apartment) benefitted from heat from their neighbours. In experiments like this is is very difficult to measure heat flow across party walls and floors etc. because you need sensors on both sides. Hence most heating experiments stick to detached (ideal) or semi-detached houses.
The carbon savings may be minimal. If you switch to a heat pump and use zero-carbon electricity there are no carbon savings from the home itself. However, reducing heating demand also reduces the need to build more expensive infrastructure to provide the extra electricity. If savings can be made at very low cost – just some more jumpers and heated blankets, this is very cost effective. The difficulty is to change the social norms.
Conclusions
- It is possible for healthy people to adapt to cooler homes using appropriate clothing and occasional use of personal heating devices. This does take time - weeks to months. The biggest barrier is in changing social norms.
- This is a very low cost way to reduce energy consumption for heating, at least for bills. The consequences for carbon emissions depend on what you consider as the alternative scenario - if that is a heat pump with renewable electricity then the carbon savings are only from needing less new infrastructure.
- There are potential risks for health. In particular high humidity allowing mould growth is a risk both for the human residents and for the fabric of the home. For people, cold homes can mean high blood pressure and risk of stroke.
Another common approach is to turn down the thermostat and provide additional heating in one room, often an electric heater. As a carbon saving approach this is fine. For bill saving, this may backfire because the electric fire is much more expensive to run than gas central heating. Even if there is no heat leakage from the warm room to the others (and there will always be some), you will only save on bills if the one room is less than 20% of the home*.
Whatever you do, my advice is to adjust the thermostat gradually - at the most by 1°C per week. Here are some more tips on saving energy at home from Transition Cambridge.
* Based on the gas boiler being 85% efficient, electricity at 24.86p/kW and gas at 6.34p/kWh)
[1] New insights into thermal comfort sufficiency in dwellings (Geoffrey van Moeseke, Jean Sobczac, Denis de Grave, Gregoire Wallenborn, Amelie Anciaux, Buildings and Cities) 2024
[2] Measured winter and spring-time indoor temperatures in UK homes over the period 1969–2010: A review and synthesis (K. Vadodaria, D.L. Loveday, V. Haines, Energy Policy) 2024.
[3] Cold homes are associated with poor biomarkers and less blood pressure check-up: English Longitudinal Study of Ageing, 2012–2013 (I Shiue, Environ Sci Pollut Res 23, 7055–7059) 2016
[4] Minimum home temperature thresholds for health in winter – A systematic literature review (Public Health England) 2014
Great analysis Nicola. My better half governs the target internal temperature at home, which I find too high for some of the same reasons as these participants. The cooler my surroundings the more alert I feel. Warm = sleepy for me. I assume there are some shared adaptation attributes between adapting to a lower thermostat and getting used to cold showers / outdoor swimming - the overton window of homeostasis shifts with repeat exposure
ReplyDeleteI've experimented with lower temperatures/heating at home too. Like Anonymous above and the Belgians in the study you cite, I find that 'normal' temperatures of 21C-plus now make me drowsy. I also tried, then discarded, heated clothing.
ReplyDeleteOne other benefit of reduced heating at home, not listed above, is that you feel a stronger connection to the outside/natural world. On a really cold day, with limited heating, the house feels cold. (This is a good reminder to feed the birds.) The north side of the house also feels markedly cooler than the south. Central heating on a fixed 20C thermostat setting means you lose this connection.
On the association between cold homes and poor health, we should be careful about ascribing causality: cold homes are often cold because occupants cannot afford to heat them adequately. If they lack the income for fuel bills, they may also lack resources for decent food and medical care. Poor households are also disproportionately likely to smoke and/or drink heavily.
My mother, who is 82 and not always in good health, has also adopted reduced heating/indoor temperatures - for financial reasons. She uses electric blankets and a heated jacket, and she has cut her gas bill by about 60%. She says she is perfectly comfortable now at 16C (I would prefer her to use a little more heating).
She also has a dog to keep her feet warm (!). I notice that pets are conspicuously absent from the literature on thermal comfort...