Heating debate

Thermostat with friendCentral heating systems have interfaces, and many of us interact with them every day, even if only by experiencing their effects.

But there’s a lot of room for improvement. They’re systems where (unlike, say, a car) we don’t generally get instantaneous feedback on the changes we make to settings or the interactions we have with the interface. It’s a slow feedback loop. We don’t necessarily have correct mental models of how they work, yet the systems cost us (a lot of) money. How effectively do we use them? Around 60% of UK domestic energy use goes on space heating, and 24% on water heating. (See this Building Research Establishment report [PDF] for more detailed breakdowns.) That 84% cost me and my girlfriend £430 last year. It’s worth thinking about from a financial point of view, regardless of the environmental aspects.

Frankie Roberto and colleagues at Rattle Research have carried out a brilliant exercise in exploratory design thinking about central heating*:

Heating systems are something we all interact with, especially in the depths of winter where we depend on them, and yet there seems to have been very little evolution in the design of their interfaces. What’s more, with an ever increasing focus on energy efficiency, both from an environmental and economic standpoint, there’s a need for heating systems and their interfaces to be smarter, more efficient and transparent.

Design Monday #1 – Central Heating (short version) from Rattle on Vimeo.

Read the full post.

The Rattle team think through existing systems and consider a number of possible revisions to improve the way that information is presented to users, and the level of control that it might be useful for users to have. This is a great piece of work, impressive and very thorough, and it’s interesting to see how their thinking evolved: I get the impression that (as service designers) they’re a lot more focused on users’ needs than the designers of many heating systems are. It’s also an exciting thing for a design company to be able to take time to address problems outside their immediate sphere, since they’re bringing a whole new level of domain expertise to it.

The ‘I’m working’ indicator is a really good idea – it reminds me of some higher-end car tyre air pumps at petrol stations where you can just set the pressure you want to achieve, and the pump cuts out (and alerts you) when it reaches it. But the idea of doing away with the ‘desired temperature’ setting and just having warmer/colder is also interesting – “forc[ing] people to always make decisions based upon how they’re feeling right now”.

Equally the ‘shift to service’ approach of having an API and making clever use of it has a big potential to help in energy saving (and cost saving for the user), especially if the usage data were (anonymised or otherwise) available for analysis. Just being able to tell users “it’s costing you £X more to heat your home than it does for a similar family in a similar house down the road – if you insulated better you could save £X every month” would be an interesting mechanism for persuasion. As with so many things, it relies on having that API or other interface available in the first place…

Folk theory of thermostats

The ‘folk theory of thermostats’ which Frankie mentions, popularised in Don Norman’s The Psychology / Design of Everday Things, has long intrigued me:

There are two commonly held folk theories about thermostats: the timer theory and the valve theory. The timer theory proposes that the thermostat simply controls the relative proportion of time that the device stays on. Set the thermostat midway, and the device is on about half the time; set it all the way up and the device is on all the time. Hence, to heat or cool something most quickly, set the thermostat so that the device is on all the time. The valve theory proposes that the thermostat controls how much heat (or cold) comes out of the device. Turn the thermostat all the way up, and you get the maximum heating or cooling. The correct story is that the thermostat is just an on-off switch. Setting the thermostat at one extreme cannot affect how long it takes to reach the desired temperature.

People’s mental models of heating systems are often stereotyped or played with (as we’ve discussed before here), but as Willett Kempton found out in a classic study, there are some nuanced versions of the theories, which, in practice, are perhaps not as silly as Norman suggests. People satisfice.

Say you come in from outdoors, and are cold. Because of the delay in your exposed skin warming up to room temperature, it surely does warm you more quickly if you stand near something that’s hotter than you actually want to be, e.g. a log fire / stove. So the heuristic of ‘turning up the heat to more than you need, in order to feel warmer more quickly’ is pretty understandable, especially when the temperature controlling the thermostat is the temperature of the thermocouple/probe/whatever and not actually the body temperature of the users themselves. (That would be a good innovation in itself, of course!) Am I wrong?

Given that a lot of people do try to control heating systems as if they worked on the valve model, would it be sensible to develop one which did? Do they already exist?

*Rattle’s second ‘Design Monday’ session, on ‘Lunch’, is also well worth a look.


  1. Rich

    I’m glad you mentioned the Design of Everyday Things because over the years I’ve been buying it for lots of people, particularly my friends who have cursed themselves with brand new, expensive but unworkable kitchens. I think the real problem with kitchen appliances is that you simply cannot buy well-designed ones. There is no market for them. Not enough people know that hob controls shouldn’t be in a straight line, clocks should be adjustable without a degree in electronics, fridge settings shouldn’t go from “1” to “5”, and ovens should have accurate thermometers.

    If that’s the way people spend money on a major discretionary expense, how much less can we expect heating controls to improve. Most are bought for the cheapest possible price by builders and never changed by householders unless they physically break down.

  2. Dave

    I think the mental model for the thermostat is affected by the actual workings of automobile heater controls (which, unless your ride is new or luxe are not thermostats).

    It’s quite common to get into a freezing car in the winter (or a hot one in the summer) and to want to get the temperature livable ASAP. In the car, cranking the temperature control to one extreme or the other WILL get the desired result.

    There are two types of coolant-based heater controls in regular use: one is a coolant valve that controls the flow of coolant through the heater core. The other is an air-mixture valve that mixes cooler outside air with air blown across an always-on-full heater core. Both of these controls demonstrate the valve effect and (wrongly) train the human to think the home thermostat works like this.

    On the “cool” side, the “Max A/C” button and air mixing controls reinforce the valve mental model…


  3. If you’re thinking about thermostats and temperature and ways of controlling them, this project of mine (from the industrially sponsored project at Brunel with Boeing and BA, in 2006) might be interesting: http://www.mayonissen.com/work/boeing/

    In contrast to a normal house thermostat, where only a small number of people (who usually all know each other) experience the change and a consensus generally emerges, I was looking at how one might design a system for use in a space where lots of people might want different temperatures. Like the Rattle project I only had two relative options, warmer and cooler, although you might consider no action – ie, ‘I’m happy with the current temperature’ – as a choice too. If the preset was perfect, nobody would want it warmer or cooler; if it was only slightly off, only a few people (the pickiest ones) would request a change in temperature. If it was completely off, or had swung wildly one way or the other, even the most tolerant passengers would feel a need to make a request for hotter or colder. I also separated immediate feedback from the primary change the interaction would result in. I’d love to test the system and the underlying logic, but I’ve never had the opportunity.

    Would be happy to hear any feedback on the project and the ideas in it – for what it’s worth Boeing and BA weren’t interested!

  4. Somnambulian Pirates

    Another problem with thermostats is the fact that the controller is controlling the temperature of a large area by sampling from a single point. Instead of one central heat source, a bunch of heat sources, each with their own thermostat, might be preferable. For the heat unit nearest the door, you could add a ‘warmup’ button that blasts heat for 5 minutes– so someone just coming in can warm up without adjusting the thermostat.

    If distributed heat sources are too inefficient, then one could still use multiple thermostats and blowers to independently draw heat from a central source.

    Rich is also correct that poorly-designed controllers are a problem. Problem is, even a well-designed thermostat will fail over the life of unit. A tax credit or government subsidy for annual thermostat calibration could help here.

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  6. It also helps if the thermostat measures the temperature of most of the air in the room, rather than the air near the thermostat. Ours is on an exterior wall, so when it’s very cold outside, the room is like an oven, so we have to turn the thermostat down – which is a little perverse.

    As for voting systems, perhaps someone could invent a wifi/bluetooth/GPRS sensor that fit into a watch/phone/PDA or dedicated pendant/bracelet? This would relay the skin temperature of the wearer such that it could be determined whether they were ‘hot’ or ‘cold’ and could adjust the heating accordingly. Naturally, those who have been in the heated area longer get more votes than those who’ve just arrived.

  7. Dan

    Those are some great points about the lack of granularity (if you like) of the sampling that conventional thermostat-controlled home heating systems have.

    Multiple heat ‘outlets’ even if they’re drawing from a central source as in Somnambulian Pirates’ idea would be very useful where there are people with different body temperatures, or perceptions of temperature (i.e. always, as Mayo’s project addresses) and where different parts of the room have different air temperatures due to cooling losses (i.e. everywhere, until thermal equilibrium is reached throughout the entire system – in the case of Crosbie’s wall, that would mean the entire outside world too!).

    Dave’s example of the car heater controls is, indeed probably where the prevalent mental model comes from – and it does intuitively make sense from a user’s point of view.

    Some flats/offices have forced hot-air heating systems, where (I presume) there is a central furnace / other heater with fans that pump the air to every room, at some (centrally determined) temperature, and the vents on the outlets in individual rooms can be shut off as required to reduce the outflow of hot air (and thus control the temperature locally). The flat I live in now once had this (there are lots of redundant vents around) but it’s no longer in use.

    This, then is surely a real type of central heating which does accord with the valve model (though I guess only up to the point where all the vents are open and the air coming out is at the maximum temperature set by the landlord or whoever.

    Rich’s point about the sort of products that people actually buy, even though better alternatives are available, is a good one. I suppose it often comes down to whether or not people realise the effects/annoyances/costs that different designs are potentially going to cause, in everyday life, over the life of the product. That was part of the point behind Norman’s book, I think – making these issues available to the public – but the fact that not even all designers think too deeply about it probably shows how big the problem is.

  8. Perhaps a third button for ‘this feels good’, which keeps the room at the current temp.

    Also I think the system should be automated… like smart fridges… that use sophisticated algorithms to learn what we like at different times. this should then be the default, with the three buttons for adjustment.

    just my 2c after a glass of red 😉

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