What Does Quiet Mode Actually Do On A Heat Pump?

Many modern heat pumps include a setting called quiet mode, sometimes labelled silent mode depending on the manufacturer. As the name suggests, it reduces the noise produced by the outdoor unit, which is useful when the unit is close to a bedroom window, near a neighbouring property, or installed in a quieter residential area. Most manufacturers achieve this by limiting the fan speed, compressor speed, and maximum output simultaneously. The result is a noticeably quieter unit, particularly during evening and overnight periods.

What quiet mode does not do, however, is reduce your heating costs in any meaningful way. The property still needs the same amount of heat regardless of whether quiet mode is active or not. If the heat pump is producing less heat because of the restriction, it will simply need to run for longer to achieve the same result. On a mild day this may not matter much, but during colder weather the situation is very different.

During cold spells, a correctly sized heat pump may already be working close to its design output just to keep the property at temperature. Reducing available capacity through quiet mode in those conditions can directly affect the system's ability to do its job. The effects tend to show up as slower warm-up times in the morning, rooms struggling to reach their target temperature, extended run times, and reduced recovery after overnight setback periods. Homes with underfloor heating are particularly vulnerable to this because of the large amount of energy required to bring a cooled floor back up to temperature. If quiet mode is restricting output during a cold morning when the system most needs to recover, comfort levels can drop noticeably even in a system that was correctly designed and installed. Our article on why your heat pump isn't reaching target temperature covers this kind of shortfall in more detail.

We came across a very clear example of quiet mode causing exactly this kind of problem. An elderly homeowner contacted us because her house simply wasn't warming up properly. The installing company had already returned several times. The heat loss calculations looked reasonable, the radiators had been upgraded, and the weather compensation had even been removed in favour of a fixed 55°C flow temperature in an attempt to resolve the issue. Despite all of this, the property continued to struggle. When we reviewed the controller settings in detail, we found a quiet mode schedule buried in the installer settings of the LG controller. The heat pump's output had been restricted throughout the night and into the morning, which was preventing the property from recovering the temperature lost overnight. Once the schedule was removed, the homeowner reported that the house was warm and comfortable again within a couple of days. You can read the full account in the Elderly Homeowner Told Her Heat Pump Was Fine – One Setting Was Stopping The House From Heating Properly case study.

For most correctly designed systems, quiet mode is best treated as a feature for specific situations rather than something left permanently enabled. Modern heat pumps already modulate their output automatically when heating demand is low the system will slow itself down without any intervention, so running quiet mode permanently tends to restrict output unnecessarily without providing any real benefit. It can also affect hot water production, since a heat pump taking longer to reheat the cylinder leaves less time available for space heating, which matters most during the colder months when demand from both is at its highest.

There is one situation where quiet mode makes more sense: during the summer months when the heat pump is primarily producing domestic hot water and has plenty of spare capacity. Depending on the manufacturer and controller, some systems can run quiet mode during hot water production with very little impact on comfort. But as a general rule, if you choose to use quiet mode overnight during winter, you should accept that the property may cool slightly and will need a few hours in the morning to fully recover. Our guide on how to set a heat pump for maximum efficiency covers the settings that have the biggest impact on daily performance, and our article on what flow temperature your heat pump should run at explains how output capacity and flow temperature interact both worth reading if your system has been adjusted in an attempt to fix comfort issues.

If your heat pump isn't performing as it should and you're not sure whether quiet mode or another setting might be responsible, our Fix My Heat Pump service can review your controller settings and system configuration to identify what is causing the problem. You might also find it useful to look at the Detached Home in Berkshire – Weather Compensation Disabled By Installer At Handover case study, which shows how a single setting change at handover had a similar effect on overall heating performance, or the Why This Heat Pump Seemed To Have A Mind Of Its Own case study, which is another example of a hidden schedule causing unexplained behaviour.