A mini-split air handler in the corner of a room just below the ceiling with a vent installed

Mini-split heat pumps are permanently installed in the home to provide both heating and cooling with a simple, push-button remote.

Their ease of installation and eco-friendly technology make them a popular choice for home HVAC solutions.

No ductwork means they can provide air conditioning for homes with boiler and baseboard heat.

Like central air conditioners, all mini-splits generate condensation during regular operation in the summer.

The condensate is just water that is removed from the air, but where does that excess water drain to? Do you need to install a special drain for the unit? Or maybe even a condensate pump?

How Does a Mini-Split Drain From The Wall or Ceiling?

Mini-splits come with a built-in drain line attached to the indoor air handler. If you are looking at the unit on the wall, you probably won’t even see it. It’s wrapped up with the lineset that goes outside. 

This drain line is where the indoor unit gets rid of that excess condensation. If installed correctly, it should drain outside.

What Is a Mini-Split?

If you’re not quite sure what a mini split is…

Mini splits are heat pump systems that can provide both heating and cooling. The majority of them are ductless, though you can get ducted versions for heating in bathrooms and attics. 

Mini splits are fully electric and rely on heat transfer (through use of refrigerant) to heat and cool. Like an air conditioner, they use the refrigerant to move heat from inside to outside. But unlike an AC system, they can work in reverse and pump the heat back inside.

There are two main components to the system: the outdoor unit and the indoor unit.

The outdoor unit is called the condenser and looks like a thinner, rectangular shaped air conditioner. 

The indoor unit is called the air handler or “head.” These are rectangular, wall mounted units equipped with fans to circulate warm and cool air from the system.

A single condenser can have one or several indoor heads.

A ductless mini-split compressor on the external wall of a home

The two pieces are connected to each other by the copper refrigerant lines that go through the wall. In most cases, the condensate drain goes through the wall here as well.

The refrigerant lines are often enclosed in conduits, such as “line hide,” which conceals them from view and protects them from weather and rodents with sharp teeth.

How to Drain a Mini-Split

Mini-splits have the option to fit the drain on either side of the unit.

Most of the time, the head unit is mounted on an external wall. In this case, the condensate drain passes directly through the wall, is routed down the side of the house, and drips onto the ground, where it seeps away.

A ductless mini-split condensate drain at the bottom of line near the compressor
Courtesy of Quality Heating and Sheet Metal Company, Inc.

If the head unit is mounted to an interior wall, or cannot use gravity to drain, you will need to install a condensate pump. These are easy to install and will pump the waste water into your main drain. 

However, 95% of mini split installation configurations have the drain going through the outside wall.

Avoiding Draining Problems

Make Sure Your Indoor Unit is Level

A mini-split is carefully designed to handle condensate that forms during operation.

If it is not installed perfectly level, the water will not be able to drain in the way it should. Double check that the bracket is perfectly level before hanging the unit and you should be just fine.

Test the Condensate Drain

If your mini-split was installed during the winter and not adequately tested, you might not notice any problem during the heating season. However, when summer arrives, and you turn on cooling mode, you could find you have a leak.

Ensure the Drain Has the Correct Slope

Water flows downhill.

You must ensure at least a 1% slope all the way along the condensate drain or your drain line could back up and shut down the unit.

Sometimes condensate drains are held in place with clips and can sag between them where they are not supported. Sagging creates short sections where the water can sit instead of draining away, which can cause blockages.

A helpful installation tip is to drill the hole through the wall behind your air handler at a downward angle, which helps to ensure the pipes are angled down immediately behind the air handler and prevents problems right at the top of the drain. 

All in all, mini split drain lines are one of the most simple aspects of the installation process. As long as the indoor head is level and the drain line flows downward, you should be good to go.

One Comment

  1. “We are not talking about large volumes of water here, so there is not necessarily a requirement to direct a condensate drain into your main drain, although this can be an option.”

    Having a hard time finding out how much drainage to expect. In planning stages for mini-split for 533 sq ft apartment. Avg humdity 72.

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