In the UK, most households rely on gas boilers for heating and hot water. This quietly operating machine accounts for a significant portion of household energy expenditure, yet many have never adjusted the water temperature, resulting in years of wasted money and unnecessary greenhouse gas emissions. In fact, simply lowering the flow temperature a bit can keep homes warm while substantially reducing costs.
Government guidelines are clear: for system boilers with a hot water tank, the flow temperature should be set at 60°C to prevent Legionnaires’ disease; for combi boilers, which do not have a tank and carry a lower risk, the hot water temperature can be set even lower, such as 55°C. The risk of Legionnaires’ disease is already low in typical homes, especially since Hong Kong residents tend to shower daily, leading to frequent water use and preventing hot water from stagnating in pipes. The real high-risk settings are large buildings like offices, shopping malls, and hotels, where complex piping and uneven water usage patterns make stagnation more likely.
Many believe that lowering the flow temperature will make indoor spaces uncomfortably cool, but this is a misconception. For most UK homes, a heating flow temperature of 55°C to 60°C is sufficient for daily needs. In rare cases where insulation is poor or radiators are undersized, it may feel less warm, but simply adjusting the dial higher poses no risk.
Why do many boiler dials feature an ‘e’, typically set around 67°C? This is a relic from the past, marking the ‘economy mode’ based on the thinking of non-condensing boilers: heat quickly at high temperatures and then shut off with the thermostat, believing that ‘high heat on, quick off’ is more gas-efficient. However, most modern boilers are condensing types, which can recover heat from the flue gases if the return water temperature is low enough, thus improving efficiency. Therefore, the ‘e’ at 67°C is outdated today.
A more practical reason is that gas engineers often raise the flow temperature during annual inspections to allow radiators to warm up more quickly for testing, but they frequently forget to reset it afterward. As a result, many households mistakenly believe that higher temperatures represent the ‘correct setting’, leading to increased gas consumption year after year.
Adjusting the temperature is straightforward: simply turn the dial. Typically, the boiler panel will have separate temperature settings for ‘heating’ and ‘hot water’. Set the heating to around 55°C or 60°C, and adjust the hot water according to personal needs, with the option to revert at any time.
How much can one save? For a typical three-bedroom UK household, lowering the heating flow temperature from 67°C to 55°C could conservatively reduce gas usage by about 6% to 10%. If annual gas expenses are around £1,000, this translates to annual savings of approximately £60 to £100; the more gas consumed, the greater the savings. Coupled with an appropriate heating schedule and room temperature settings, actual savings could be even higher, with no noticeable difference in indoor comfort.
When discussing heating, one cannot overlook TRVs (thermostatic radiator valves). Many people feel their radiators are not warm enough and turn the TRV to 5, mistakenly believing that higher settings yield more heat. In reality, the TRV numbers indicate the target room temperature, with 3 roughly equating to 20°C, which is comfortable enough. If a radiator is occasionally cold, it does not necessarily mean the heating is off; it could simply mean the room has reached the desired temperature or that the boiler is temporarily paused according to the schedule. Radiators do not need to be hot all day, as this would only waste energy.
While this article discusses how to use gas boilers more efficiently, in the long run, heat pumps remain a superior solution for heating and hot water. Gas boilers achieve a maximum efficiency of about 90%, whereas heat pumps can deliver three to four times that, outputting more heat from the same unit of electricity, far surpassing traditional equipment in efficiency.
Lowering the dial does not change habits or reduce warmth, yet it can save money, gas, and emissions. If millions of households are willing to lower their flow temperatures slightly, the national gas consumption would significantly decline, and your winter would remain just as warm, only more economical, contributing to the protection of the planet.
