The hole
Making the hole in the wall through which the refrigerant, condensate and unit interconnecting cable pass from inside to outside is usually the most significant step of a mini-split install.
Location
The location of the hole is a balance of:
- efficiency (minimising refrigerant pipe length)
- appearance (minimising or eliminating trunking runs, especially inside)
- practicality (including the structural integrity of the building)
Most indoor units come with a template or installation board to aid fixing to the wall. This shows positions for the hole if positioned behind the unit itself. If this isn’t practical, the exit position for the pipework marked on the template should be used as a basis for the pipe runs.
Size and drilling
The install instructions should give the hole size required, typically around 65mm or 70mm.
For brick and breeze block, carbide tipped hole saws with an SDS plus drill provide a straightforward solution. HSS hole saws are available to drill wood and plasterboard. The hole should tilt down slightly to the outside to reduce the risk of water ingress.
For neatest results, drill from one side until the centre pilot drill appears on the other side. Then drill back from the other side using the pilot hole created.
Sleeve
The hole should be lined to prevent dust and debris ingress from the wall. This also makes sealing around the pipes and cables easier.
Dedicated sleeves are available, but a cheap and effective solution is to use a piece of rainwater downpipe. 68mm downpipe lines a 70mm hole very well!
It is important not to permanently fix the pipe work in the sleeve before the system is tested. Adjustments will need to be made when flaring and connecting the pipes to the indoor unit connections. Sealing with expanding foam or mastic to make the hole weatherproof should be done after the system is operational.