On a 1930s semi the useful decision is the side passage or the rear wall, plus which one room you will cool first. These houses often have a bay, a chimney and a loft route, and some have a narrow early cavity rather than a solid wall. Do not assume either. Survey the wall you will drill, the consumer unit and the outdoor spot. A multi-split only works if pipe length, height and that one lawful spot can reach every room. An F-gas certified company installs the pair.
A soil pipe and a gate post in a passage under a metre
Many 1930s semis have a side passage or a driveway beside the kitchen. That is a genuine outdoor place when it is wide enough for airflow and service, and when the neighbour's windows are not hard against it. A passage under a metre, blocked by a soil pipe and a gate post, is not a free gift. Measure it. Say whether the passage is wide enough to walk down, so nobody prices a fantasy gap. Photos of the side passage, even if it is cramped, the rear elevation, the room you want, and the consumer unit belong with that measurement. In England, Planning Portal conditions still apply to whichever elevation you use.
The bay bedroom and the chimney between the semis
The front bedroom over the bay is often the hot one, and the bay itself is a weak place for a bracket. A side wall in that room, drilling toward the passage, can be the short pipe.
- Use a side passage only if the clearances are real.
- Rear wall if the passage is too tight or missing.
- Keep the condenser off the bay window.
- Confirm cavity or solid wall before the drill method is priced.
Loft pipes, the board and a kitchen gully
The loft in a 1930s semi is a possible pipe route to the rear, if the joists and the tanks leave a path and the length still passes. It is also where condensate must not drip onto a ceiling. Gravity to a kitchen gully or a pump with a written route belongs on the quote. Consumer units in these houses are often replacements already, and sometimes they are not. A spare way for a 230 V circuit is the question. As a 2026 illustration, one room on a genuine side or rear wall is often in the low thousands including VAT. A board change, a tight passage that forces scaffold, or making good pebbledash are the usual extras.
The rear wall when the side is not a gift
If your semi has no side access, do not invent one in the quote. Use the rear wall and bring the equipment through the house. The front bay is a poor outdoor spot: it faces the street and the room you are trying to keep quiet. A chimney breast between the semis is not a drilling target until it is known to be redundant and clear of flues. Decide the room by when you suffer. The front bedroom at night and a rear kitchen in the late sun are different jobs. One single split is a complete first step. Adding the second room later needs its own survey. A new indoor unit on the first outdoor unit is usually not a mix-and-match unless the combination was listed from the start. The side passage is the right outdoor spot only when airflow, service access and the neighbour's windows allow it. A tight, noisy slot should push the unit to the rear.
Stop if the quote invents a side gap or a cavity
Do not accept a cavity-tie detail unless a cavity is there. Some 1930s semis have an early cavity, some are solid, and bays are different again. The survey should say what it is drilling. Ask for one room first, with model codes, wall type, drain and the outdoor position. If you want a second room, ask whether the same spot stays inside the pipe and height limits, or whether that room should wait. Front bedrooms and a rear kitchen together work only if the pipe length, the height and one lawful outdoor spot all work. If the bay bedrooms and the kitchen pull in opposite directions, do the room you use most.
Frequently asked questions
Do all 1930s semis have a cavity?
No. Some have an early cavity, some are solid, and bays are different again. The survey should say what it is drilling. Do not accept a cavity-tie detail unless a cavity is there.
Is the side passage always the right outdoor spot?
Only when airflow, service access and the neighbour's windows allow it. A tight, noisy slot should push the unit to the rear.
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How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.