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Choosing thermostats

Explaining thermostat features and benefits to the customer

The whole point of replacing a heating thermostat is to give the user something better and new. A decade or so ago just taking out an old electromechanical device and replacing it with a more-accurate electronic one was enough to please people. The extra accuracy these devices provided should, in theory, have reduced the tendency for heating over- and under-shoot and increased comfort levels. However, this still didn’t significantly reduce the number of on/offs (boiler cycling) on a standard boiler of the time and there wasn’t much energy saving going on. So, they didn’t do much that was extra or new, but they looked good.  

Now we expect sophisticated programmable room thermostats as the norm. Even those without integral timing offer a host of new features to take advantage of improvements in boiler design such as the ability to modulate seamlessly between a fixed low fire rate and a high fire rate. It’s as well to be sure you understand them before your customer asks.

First, remember to brief householders on the basics. Turning a programmable room thermostat to a higher setting will not make the room heat up any faster. How quickly the room heats up depends on the design of their heating system: the size of boiler and radiators. Neither does the setting affect how quickly the room cools down. The way to set and use a programmable room thermostat is to find the lowest temperature settings that are comfortable at the different times of day selected, and then leave it alone to do its job. 

There are a few other settings that they might not be so familiar with.

Programming times: When you first decide with the customer whether weekday/weekend (5-2) or individual (7) day programming is required you may need to move a jumper on the rear of the product. After any change of jumper position, reset may need to be pressed, which will return the unit to default time and programme. So, talk to them, and make the call early. The same may go for selecting swing control and optimum start settings (see below) although this is not the case with good WiFi controlled devices, where the user should be able to change these settings at will.

Swing control enables users to choose the range around a set point temperature. Within this range the thermostat will not turn the heating on and off and cycle the boiler, so reducing wear and tear and minimising the energy loss that comes from gas purging each time the boiler fires and deactivates. Short cycling adds to wear and tear on a boiler and can also be annoyingly noisy. It is much more energy efficient to let the temperature rise and fall a degree or so and then run the heating/cooling for a longer time. 

Typical swing options for domestic use are 1.0o and 0.5o. Choosing a 1.0o swing around a target set temperature of 20o  simply means that the heating will not be switched on or off until the temperature is higher than 21o or lower than 19o. The difference between 1.0o and 0.5o may not seem to be all that significant, but in practice people do notice small changes in temperature, especially the very young and the elderly. The wider range may be the best choice where there’s a lot of people traffic, doors are being opened and closed a lot or were, God forbid in this day and age, the space is badly insulated.

Night setback lowers the room temperature at night, which reduces heating costs. Conveniently, users don’t need to work out, or programme in, different settings.

Optimum Start is a feature that enables the thermostat to learn the response of the system it is controlling and work out how long it will take to heat up the property. These thermostats work out the best time to switch on to ensure that the desired temperature is reached at the right time. Before the boiler fires up the actual room temperature is checked and if appropriate, firing may be delayed, thus saving fuel while still ensuring the homeowners will arrive to a warm and welcoming home. No longer do they householders have to make a wild guess about when the programme the heating to turn on.

Proportional Control is another function that helps to eliminate the overshoot that can be associated with standard on/off control and lead to unnecessary short cycling. When Proportional Control is selected, it decreases the power used by the heating system as the temperature approaches target so that there is a ‘soft landing’ rather than overshoot  

Seems like a lot to remember? Well, as the saying goes, if all else fails, read the instructions. You can find all of ours ready to download at

This article first appeared in Professional Electrician, October 2018.

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