When the weather is very cold outside we quite often get calls from end users saying their units are not heating very well.

It is a well known fact that the heating capacity of any heat pump falls dramatically when it is cold outside. It is not uncommon to experience a 40% reduction if the temperature drops from +15 to -15 degrees celsius, despite manufacturers claims nothing can be done about this it's just one of the laws of physics.

What is not often discussed is what happens if it’s very cold inside. If the room temperature falls below 10 degrees celsius, your unit has a huge struggle to bring up the room temperature.

This is exactly the same problem you experience with wet systems and boilers, if your house get very cold because you have left the central heating switched off it would be stupid to expect it to immediately reheat the house as soon as it is switched on.

It can take the units many hours to drag the temperature of the room and the building fabric up from these cold temperatures.

Unfortunately people think aircon is different from any other heating systems and expect it to drag the room temperature from arctic temperatures to comfortable conditions in a few seconds.

To avoid this happening one of two solutions can be used, the first is to run the unit 24 hours a day at low set point to maintain the room temperature, just like you do with your normal central heating when it’s cold. Or secondly install a frost thermostat which starts the aircon if the room temperature is low.

Frost thermostats are rarely fitted to air-conditioning systems as standard so you will need to ask your system supplier to advise on how to do this before purchasing the kit.