Are air source heat pumps noisy?

The simple answer is NO but what is noisy? Modern air source heat pumps are significantly quieter than units produced say 5 years ago. This is primarily due to advances in the development of fan technology and improved chassis design which reduces vibration. 99% of sound generated by an air source heat pump is the movement of air. The sound levels will vary depending on the ambient temperature. The colder it is outside the faster the fan spins and vice versa. In the middle of summer the fan may not even spin.

For the purposes of the MCS Planning Standards for air source heat pumps the back ground noise is assumed to be 40 dBa or lower. For compliance with planning regulations and permitted development rights the air source heat pump must be 42 dBa or lower from the assessment position.  The assessment position is the distance between the unit and a neighbouring property.

The positioning of the unit is critical to meeting the maximum sound levels. Obstacles such as walls and fences can increase the noise levels over the design conditions. A well designed air source heat pump system must allow for the displacement of the air. This not only reduces noise but also increases the efficiency of the heat pump.

When the noise exceeds the maximum permitted levels the unit can be installed in an acoustic enclosure or sitted far enough from the assessment position to meet the regulations. Heat pumps can be located up to 30m from the property before other design considerations are imposed.

To reduce sound levels  manufactures are encouraged to meet the standards set out by the Noise Abatement Society and  awarded the Quiet Note if the heat pump is within the standards. The Mitsubishi Ecodan was the first heat pump to be awarded the Quiet Note in the UK.