Ductless mini split installation: what to know

What the job involves, what changes the price, and what to ask a pro.

What ductless mini split installation is

A ductless mini-split installation mounts an indoor wall or ceiling unit, sets an outdoor compressor, connects them with a refrigerant line set and wiring, and starts the system for heating, cooling or both. People choose it for rooms that have no ducts, for additions, or for zones that the main system heats or cools poorly.

Signs you need it

  • The house has rooms with no ductwork, such as a converted garage, a sunroom or a finished attic.
  • One room stays hot or cold while the rest of the house is comfortable.
  • You are adding an addition and the existing system cannot reach it.
  • Window units are blocking views, taking up outlets or leaking air, and you want a permanent cooling solution.
  • You want heating and cooling in the same system, and the old heat source is being replaced.
  • A room with electric baseboard or space heaters needs a more efficient heating and cooling option

What the pro does

  • Pick the indoor unit location and the outdoor compressor spot, checking clearances, sun exposure and the wall for the line set.
  • Drill the wall penetration, usually through a sleeve, and mount the indoor wall bracket at the height that clears the air flow.
  • Set the outdoor compressor on a level pad or wall bracket, with isolation pads to reduce vibration.
  • Connect the refrigerant line set, pull a vacuum on the lines to remove air and moisture, then charge the system as a certified technician.
  • Run the power and control wiring, install the outdoor disconnect, and route the condensate drain so it slopes away from the unit.
  • Commission the system by testing heating and cooling modes, the drain flow and the remote controls, then walk the homeowner through the settings.

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Number of indoor heads, because each room with its own head adds mounting, lines and wiring.
  • Line set length and the wall penetration length, which can change how the lines are routed.
  • Indoor unit type, such as wall-mounted, ceiling cassette or floor-mounted, which needs different framing and drains.
  • Electrical service, such as a new dedicated circuit or a disconnect that must be added.
  • Outdoor location, such as a rooftop, a high wall or a tight side yard, which adds labor to lift and secure the compressor.
  • Condensate drain route, especially if the drain must run through finished walls or up to a condensate pump.
  • Efficiency level and features, such as inverter control or a multi-zone outdoor unit.

What a written quote should spell out

  • Each indoor unit location and the outdoor unit location, with the model and capacity of each.
  • Line set size, length and insulation, and the wall penetration method.
  • Electrical work, such as the dedicated circuit, disconnect and wire size, listed separately.
  • Vacuum and charge steps, with the refrigerant amount added and the leak test method.
  • Condensate drain route and whether a pump is needed.
  • Commissioning steps and the warranty terms for equipment and labor.

Questions to ask before you hire

  • How did you size each indoor head for its room, and what is the total capacity for the outdoor unit?
  • Where will the outdoor unit sit, and how far is it from the nearest bedroom window?
  • How will the condensate drain be routed, and does it slope all the way to a drain or outside?
  • Will you pull a vacuum on the lines and tell me the level you reached?
  • Who pulls the electrical and mechanical permits, and will the work be inspected?
  • What is the warranty on the outdoor compressor and on each indoor head?
  • Will you show me how to use the remote, the schedule and the filter cleaning?

Red flags

  • The pro puts a head in a room without checking the room size or the outdoor capacity.
  • The pro leaves the condensate drain flat or uphill from the indoor unit.
  • The pro skips the vacuum step on the lines.
  • The quote does not list the electrical work or the line set length.

What you can do yourself

You can clear the wall space and the outdoor site, and make sure the installer can reach both locations. Keep the outdoor site free of leaves and debris after the install. Refrigerant lines, the wall penetration, the electrical hookup and the charge belong to a licensed technician with refrigerant handling certification.

Licenses and permits

Ductless mini-split installation is commonly done under a contractor license, and it often requires an electrical permit for the new circuit and a mechanical permit for the system. Check with your state or local licensing agency for the requirements that apply to your job.

Ductless mini split installation questions

Can a ductless system heat as well as cool?

Yes, most ductless systems run in heating and cooling modes. Ask the installer to confirm the heating capacity at the outdoor temperatures your area sees in winter.

How many rooms can one outdoor unit serve?

It depends on the model. Multi-zone outdoor units serve several indoor heads, and the total capacity has to match what the heads need. Ask for the capacity of each head and the combined total.

Why does the indoor unit drip water?

A little condensate is normal when the unit cools. A steady drip or water pooling near the head points to a drain that is blocked, flat or uphill, and should be checked.

Can I put in a ductless system myself?

No. The refrigerant lines and charge commonly require a certification, and the electrical work often must be done by a licensed professional.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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