Wall-mounted air conditioners without an outdoor unit
Sources and calculations reviewed 28 August 2026. How we review our guidance
A wall-mounted air conditioner without a separate outdoor unit is usually a through-wall monoblock. It keeps the refrigeration circuit in one indoor cabinet and exchanges condenser air through two large wall openings. It removes the outdoor box, but it is not ventless and still alters the external wall.
Monoblock versus split system
| Feature | Through-wall monoblock | Conventional split system |
|---|---|---|
| Outdoor condenser box | No | Yes |
| External work | Usually two large grilles | Brackets/base, condenser and pipe penetration |
| Compressor location | Indoors | Outdoors |
| Indoor noise | Usually higher | Usually lower |
| Refrigerant pipe connection on site | Often avoided by sealed factory circuit | Normally required |
| Visual impact outside | Grilles | Condenser unit and pipework |
The appeal is a simpler exterior and a self-contained refrigerant circuit. The trade-offs are indoor compressor noise, wall penetrations and often lower efficiency than a well-installed split.
What installation involves
The installer must survey the wall construction and check for electrical cables, pipes, structure and hazardous materials before cutting. The two penetrations need the diameter, spacing and weather protection specified by the manufacturer.
The unit also needs:
- a structurally sound mounting position;
- suitable electrical supply and isolation;
- external clearance around both grilles;
- a condensate strategy; and
- access for filters and maintenance.
This is not equivalent to hanging a radiator on an internal wall. Cutting large external openings without understanding the construction can cause water ingress, air leakage and structural damage.
Noise and vibration
Because the compressor remains indoors, compare both the lowest and maximum sound figures. Wall structure can transmit vibration, and lightweight partitions may amplify it. Ask how isolation pads, fixings and the sleeve prevent vibration transfer.
For a bedroom, a split system is normally the quieter fixed option. If an outdoor box is prohibited, assess the monoblock’s sound character and placement rather than assuming “no outdoor unit” means silent.
Condensate and heating mode
Cooling removes moisture from indoor air. Some monoblocks evaporate condensate through the external airflow; others need a drain. Reversible models also heat, which can change drainage behaviour in cold weather. Check the exact manual rather than assuming “self-evaporating” means no drain in every operating condition.
Permissions and appearance
Two outside grilles are less bulky than a condenser but remain a facade alteration. Check local planning requirements, lease terms and freeholder rules before work, especially for flats, listed buildings and conservation areas.
Also consider neighbours: external airflow and sound need clearance even without a condenser cabinet.
Is it the right choice?
Consider a monoblock when:
- an outdoor condenser box is not acceptable;
- permanent wall openings are permitted;
- indoor compressor noise is acceptable; and
- the room can be served by one correctly sized unit.
Choose a split system when quiet operation and efficiency matter more than the outdoor-unit restriction. Choose a portable when permanent alterations are not allowed and a temporary window kit is practical.
Start with the BTU calculator, then compare installed and operating costs using the installation-cost guide and running cost calculator.