Noise from outdoor units often times exceeds noise levels allowed by legislation. As an example, the 2015 data sheet of the “Mr Slim” Zubadan Inverter Heat Pump informs whoever reads it, including the pump’s owner’s neighbors, that the Mr Slim outdoor unit generates 52 dB in heating mode. This is much more than is permitted by statute law in some countries, for example the UK, where this or similar pumps are used. Another example is Poland, where the noise level permitted in houses is 40 dB during the night, which is much more than the UK limit (35 dB), but still puts the Mr Slim outdoor unit 12 dB above the limit. In the United States, the allowed nighttime noise level was defined in 1974 as “an average 24-hr exposure limit of 55 A-weighted decibels (dBA) to protect the public from all adverse effects on health and welfare in residential areas (U.S. EPA 1974). This limit is a day– night 24-hr average noise level (LDN), with a 10-dBA penalty related to nighttime levels between 2200 and 0700 hours to account for sleep disruption and no penalty applied to daytime levels. The 10-dB( A) penalty makes the permitted U.S. nighttime noise level equal to 45 dB, which is in excess of is accepted in some European countries but less than the noise produced by some heat pumps.