A hot topic in an energy crisis: how efficiently are you using your boiler?

With the Christmas festivities getting closer, Madeleine and Matt Cage* decided they had to replace their 19-year-old boiler which was only working in 20-minute spurts. When an engineer came out to see what they needed, he simply looked at the system in place and recommended a similar machine.

What the couple soon realised was that the boiler that was in place – and which they had been told to replace with something similar – was far too big for the their four-bedroom home.

A second engineer, who took more exact readings of the size of the home and how they used their heating, recommended a much smaller system that would be more efficient and cost less to run.

A boiler that is too big is a common problem, according to Jo Alsop of The Heating Hub, an independent consultancy that focuses on energy efficiency, and it is one that only adds to the rising cost of heating our homes.

As we enter the coldest period of the year, during an energy crisis that has seen bills rocket, consumers have also been advised that there are simple measures they can put in place to achieve savings linked to boiler use.

“There is latent efficiency in every boiler, some of which can be tapped by occupants with a few simple, and safe, DIY changes,” says Alsop.

Is your boiler too big?

Most of the boilers (about 80%) sold in the UK are combi units, which provide heating and hot water. The rest are either heat-only regular boilers, or system boilers, which work with a hot-water cylinder.

All types have similar problems, in that they are often too powerful for the requirements of the home. As Alsop explains: “It’s like trying to boil water with a small pan on a large hob – there is no way of it not boiling over. That is what a big, over-sized boiler is doing. It’s too big for the heat loss of the building.

“Boilers are at their most efficient when they match the heat loss,” she says, with studies finding oversized boilers are 6-9% less efficient.

The average British home can be heated with a 6-10kW boiler on a cold day. Most heat-only and system boilers start at 11-13kW. Combi boilers need at least 24kW, but this is for instantaneous hot water, and have heating outputs of about 18kW, still too big for most homes, she says.

Due to a poor understanding of heat loss, some installers put in bigger and bigger boilers, fitting systems up to 50kW, according to Alsop. Over-sized boilers are subject to greater wear and tear, which can result in higher fuel bills.
To resolve the problem, modern boilers need to have two separate outputs, one for heating and one for hot water. Combi boilers have this automatically. But for heat-only and system boilers, the installer has to configure the system correctly, and fit the right heating controls, which does not happen in most cases, she says.

When they are set up correctly, the boiler can be “range rated” down, or adjusted to, the maximum heat requirement by installers.

Getting the flow right

Flow temperature dictates how hot the boiler heats water, and is usually set at between 70C and 80C when the combi boiler is installed. But this is too high for many boilers to operate efficiently, according to energy company EDF.

At lower temperatures, they go into condensing mode more frequently, so more heat can be captured and recycled into the system.

Combi boilers often work best when they heat radiators to 60°C or below, according to Nesta, the agency that promotes innovation. This does not mean the temperature of your home will be lower, but radiators will take slightly longer to heat up.

Adjusting it is possible yourself, but it is not the same as changing the temperature on your thermostat. The controls to change the flow temperature are on the front of the boiler.

“A government report found 70% of homes could stay warm at 60°C degree flow temperatures – 20 degrees less than most homes are set up to currently,” says Alsop.

“If a householder is particularly alert to it, they could adjust it to 50C during the milder months, and turn it back up to 60C as it gets colder, so the temperature relates to the outside temperature.”

Nesta estimates turning the temperature down could result in an energy bill saving of £112 a year.

Turn off the preheat

As combi boilers are usually placed some distance from the bathroom, it can take time for water to reach the taps.

A preheat function in some machines keeps a small amount of hot water ready, which can be sent to the hot tap quickly.

But in order to achieve this, the boiler has to fire up every 90 minutes or so, using a little bit of gas at a time. This can add up over time: The Heating Hub says there is a potential saving of up to £90 a year if this is switched off.

How to turn it off depends on the type of machine, and not all models have this feature, while some that have it cannot be turned off.

Changes in lifestyle

Making changes to the way you heat your home can result in significant savings. Turning down the thermostat by even one degree can save money. In France, the owners of private buildings have been encouraged to reduce thermostats to 19C while occupied, and lower them further to 16C overnight.

“It’s always a bit eye-rolling. But it really does work. It’s one of the biggest savers to turn from 20C to 19C,” says Alsop. Just one degree can save £117 a year off the average bill, it is claimed.

Some households leave their boiler on “long and low”, or permanently at a lower temperature for the whole day, so the machine has less work to do and spends less time in an inefficient mode trying to get up to a certain temperature.

However, Alsop says this has been shown to use more gas, and that a timed regime – where the boiler is switched on for set periods, such as two hours – is more efficient and can save £130 a year.

* Name has been changed