Tuesday, 18 November 2014

How much can you save by adding heating controls?

According to Control Your Home, we can save 40% on our heating bills by installing appropriate controls: timer, room thermostat and thermostatic radiator valves (TRVs). Although 97% of us have timers on our heating systems, only 77% have room thermostats and 49% have those and TRVs too [1]. So if you are one of the 51%, how much could you save? Where does that 40% figure come from and would it apply to you?

The 40% figure comes from tests on the 'Salford House' - an amazing test facility which has an entire house built inside an environmental test chamber. They can do tests there under any sort of weather conditions, even rain and snow. They can also simulate the behaviour of people - moving from room to room, turning on taps and so on. Field tests on real homes with ordinary people are difficult to interpret because you can't control the weather and the people living in the houses don't do the same things from one day to another. You need at least 1000s of samples to make sense of data with that level of variability. So using the Salford House is a lot easier. However, it is still only one house - is it sufficiently like your house to predict your savings?

Heating controls will only make you savings if they allow you to heat your home less than you did before. If some parts of your home are heated more than necessary, then restricting the heating in those rooms will bring you savings. The Salford House test reports include temperature graphs from the different rooms in the house. The chart below is from the second test, which is with a room thermostat in the living room set to 21C but no TRVs.

Test 2 - with timer and room thermostat set to 21C but no TRVs. From [1]

You may need to click on the chart to see it properly. If you do, you will notice that the living room, where the thermostat is, is not the warmest room in the house by a long way. The kitchen, both bedrooms and the hall are all considerably warmer. So even though the thermostat turns the heating off when the living room gets to 21C, more or less, the other rooms are warmer, in most cases around 25C.

There could be lots of reasons for this. For example, when we first moved into our current house the living room was the coldest room. It is on the north side of the house with a large bay window. The radiator always took forever to warm up, presumably because it was the last one on the the heating circuit. And even when it did, the radiator was mostly blocked by furniture (against all advice, I know, but that was the only wall big enough for the sofa). So that radiator was not as effective as it should have been.

In the Salford test house, setting TRVs to 18C in all the rooms except for the living room reduced the heating needed by 33%. This is in addition to the savings from having a room thermostat in the first place - without that the living room went up to 25C in the evening and one of the bedrooms hit 30C!

This research shows that heatings controls can make for excellent savings - if your home is overheated to start with. To check what this means for your home you need to decide if under your current regime there are rooms that get warmer than you need. If you don't have a thermostat at all you are likely to find that your home gets very warm over the course of the evening, so you may be comfortable at 7pm and very cosy indeed by 10pm.

There is good advice on the Control Your Home FAQ page, such as why it is better to have a thermostat than to manually turn the boiler off and on when you want it. There is more advice here on the Transition Cambridge website.

One thing about the Salford House that might be unusual is that the room thermostat was in the living room, not the hall. In many homes the thermostat is in the hall which is not the most important area to to keep warm. I have discussed this issue before in 'How much of your house do you heat?'

Another interesting point is what the room temperatures should be. There are no definite answers to this as people have different requirement and different sensitivities (see also 'What is a reasonable setting for my thermostat') . If you think you might like to try reducing your thermostat setting I strongly advise that you do this just a little bit at a time - just half a degree and leave it at that setting for at least a week to see if you get used to it. It can take time to adjust.

[1] Research findings from the University of Salford (www.controlyourhome.org.uk)

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