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How to ensure boilers condense - what installers need to know

Published: 05-12-2024

Maximising a boiler’s efficiency is a top priority for any installer, one of the most effective ways to achieve this is by ensuring the boiler operates in condensing mode as much as possible. A condensing boiler, when kept below temperatures of 50°C, can operate up to 10% more efficiently than when running at higher temperatures, resulting in significant energy savings and reduced emissions.

A condensing boiler recycles some of the heat that would otherwise be lost through the flue, which allows it to use less fuel to achieve the same indoor comfort level. By encouraging boilers to operate in this low-temperature, condensing mode, installers can help homeowners enjoy lower energy bills and a more eco-friendly heating solution.

Maximise condensation

The first step in optimising condensation is to assess the heating system’s requirements, ensuring that it can handle lower operating temperatures. Begin with a comprehensive heat loss calculation to determine the exact heating needs of the property and to verify that the existing radiators are correctly sized. It obviously depends on the engineer who sized the original radiators, but are the radiators sized for high temperature operation or have they been oversized and the desired room temperatures can be achieved by running them at lower boiler temperatures. Has there been remedial insulation or double or triple glazing installed since the radiators were installed again resulting in them being able to be run at lower temperatures.

Another effective strategy is to “lock” the boiler to match the system's temperature needs. By setting a maximum flow temperature that prevents the boiler from venturing into high-temperature, non-condensing ranges, the system can run more consistently in its most efficient mode. This adjustment allows the boiler to operate within a stable, low-temperature range that supports continuous condensation.

For existing combi boilers, one of the easiest ways to encourage condensation is by simply lowering the thermostat. Suggest that homeowners set the flow temperature to around 50°C and see if this setting keeps their home comfortable. If it does, the boiler is likely operating in condensing mode most of the time. During especially cold weather, they can temporarily raise the temperature for added comfort, then return to the lower setting once conditions stabilise. This minor adjustment can lead to noticeable efficiency gains.

Taking control

Adding compensation controls is another way to help a boiler stay in condensing mode. These smart controls adjust the boiler’s output automatically based on external or internal temperature changes. Weather compensation controls, for example, monitor outdoor temperatures and adjust the boiler’s flow temperature accordingly, ensuring a comfortable indoor environment while preventing unnecessary fuel consumption. Load compensation controls work similarly, but respond to indoor temperatures to maintain the desired room temperature without pushing the boiler out of condensing mode.

These smart control options are so effective that recent government guidelines increasingly recommend them as standard for new boiler installations. By keeping the boiler at the lowest necessary temperature, compensation controls not only improve efficiency but also make managing the system more convenient for homeowners.