Most outdoor units in England need no planning application. Flats, listed buildings and conservation areas are where the exceptions bite. Six questions settle it.
Guidance only, based on the permitted development rules for air source heat pumps in England (Class G) and the MCS planning standard, as read in August 2026. Rules differ in Wales, Scotland and Northern Ireland, and councils can remove permitted development rights locally. Always confirm with your local planning authority before installing.
Permitted development caps the outdoor unit at 1.5 cubic metres on a house and 0.6 cubic metres on a block of flats. The Balmair outdoor unit is designed to 0.15 cubic metres, a tenth of the house limit.
The installation must meet the MCS planning standard, whose noise limit at the neighbour's nearest window was tightened to 37 dB(A) in May 2026. Quiet hardware is not a luxury, it is what makes the permission-free route work.
Permitted development covers a single outdoor unit per property. A second unit normally needs a planning application, which is one reason to size the first one properly.
Four questions, an honest capacity recommendation, and our crew confirms it on site.