The condensate tubing for both indoor and outdoor units.
Condensate lines

Condensate is water that has condensed from the atmosphere onto the heat exchanger during cooling. A mini-split that offers both heating and cooling has condensate connections on both the indoor and outdoor units. These outlets:

  • Connect to 16mm condensate pipe.
  • Are under negligible pressure and are usually push-fit. The joints can be taped or zip tied as well.

The amount of condensate produced depends on atmospheric humidity and the cooling/heating capacity of the system. If available, terminating a condensate pipe at a drain is the easiest solution. If not, a suitable soakaway can be used, or the water can even be used for watering the garden.

Downhill draining

Condensate pipe work must flow slowly ‘downhill’ to prevent water pooling in the pipe, backflowing into the unit and causing a leak.

If the condensate from an indoor unit must go ‘uphill’ then an inline condensate pump will need to be fitted. Whilst not difficult it adds complexity, requires an additional electrical connection, and creates a point of failure.

The condensate connection on the outdoor unit is usually on the bottom panel. When floor mounting a unit, it is possible to just let the condensate flow on to the floor. If this is a hazard, a slight downhill run on a hose should be used to direct the condensate flow into a drain or soakaway.


Unlike the condensate from some boilers, mini-split condensate is only very mildly acidic - rather like rainwater. Unless you’re really concerned, limescale chippings aren’t required in a soakaway. A manufacturer of condensate pumps, Sauermann, has a comprehensive article on the subject Opens in a new window.

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