Over months dust and debris will accumulate in your heat pump components which will increase the cost of running the heat pump and decrease its life time. And the accumulation mixed with condensing water and moist air is the perfect breeding ground for harmful fungi like mold and bacteria to grow.

This article by CBC describes a case in which a family developed health issues because mold built up in their heat pump.

If you use the heat pump all year long (or the AC mode) we observed that it should be cleaned between 

12 - 18 months which matches with the recommendation of leading heat pump manufactures which recommend a deep clean every year or two.

In this time period we noticed that at least one of the following symptoms occurred that indicate the need for a cleaning according by NB Power.

- Decrease in device performance, less heating or cooling than before

- Presence of trash visible to the naked eye (mildew and dust)

- Fan louder than before

- Water dripping out of unit

- Small balls of debris discard by the device

- Odours

If you use the heat pump only for heating we observed that a deep clean would be beneficial every 2 - 3 years. 

The German Guy has cleaned hundreds of heat pump since 2019, uses commercial grade equipment and cleaning solutions specially designed for heat pumps.