Installing Minisplit Heat Pumps

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Installing a minisplit heat pump (MSHP) requires skills in carpentry, electrical wiring, and working with refrigeration equipment.
A stand provides an alternative to mounting the unit on a wall, while keeping the unit above snow level.
A wall mount is easy to install and adequate for most structures.
A wall bracket for the indoor unit. Notice the wall penetration for a right-side connection and the small cutout triangles on the mounting bracket that indicate the proper location for the center of the hole.
The back of the indoor unit, with the two refrigeration lines and the condensate drain at the bottom center.
The NEC requires a disconnect at the outdoor unit. In some cases. this may provide overcurrent protection as well.
Many Home Power readers may find the electrical wiring the easy part of an installation. Routing and connecting the refrigerant tubing can be more complex.
A tubing cutter provides a clean, even cut in the tubing. The cut should then be deburred.
Before flaring the end, put the flare nut on the tube. Flares provide a sealed connection on the refrigerant line.
Flaring provides a wide surface area that seals the joint when the flare nut is tightened.
Flaring provides a wide surface area that seals the joint when the flare nut is tightened.
The connection piping for an indoor unit with “right piping” commonly passes through an exterior wall. The flare fittings for the smaller liquid line and the larger vapor line are made outside and concealed in a line-set cover.
A technician carefully works the line set into its channel.
Nitrogen is used to pressure-test the system. If the system passes the test, the nitrogen is purged, and a vacuum pump is connected to the system to remove air and moisture.

Installing a minisplit heat pump (MSHP) requires skills in carpentry, electrical wiring, and working with refrigeration equipment. Before you jump in, here’s what you need to know.

MSHP DIY?

Occasionally, a skilled homeowner will install an MSHP. Installation requires work with 240 VAC circuits and involves refrigerant that has greenhouse gas implications, so it is important to understand the requirements and safety factors. Many jurisdictions require MSHP contractors to have an electrical contractor’s license and certification from the U.S. EPA for handling refrigerants.

System installation requires common hand tools, such as drills, drivers, wrenches, screwdrivers, levels, caulk guns, knives, multimeters, and pliers. There are also specialty tools and materials that are required, including tube flaring tools, gauges, refrigeration manifolds, a vacuum pump, torque wrenches, and a nitrogen tank and regulator. For most DIYers, it makes sense to let an electrician complete that aspect of the installation, and to use a refrigeration technician to make those hookups and charge the system.

This article explores some of the common and critical tasks associated with installing MSHPs. This isn’t meant to be a substitute for technical training but to help readers understand the scope of an installation and to avoid common pitfalls.

Structural Installation

A MSHP system consists of an outdoor unit and at least one indoor unit (see “Efficient Heating with Minisplit Heat Pumps” in HP180). The outdoor and indoor unit are connected by electrical wiring and insulated refrigeration tubing. These units need to remain fixed in specific locations.

There are three common methods for supporting an outdoor unit:

  • On a mounting frame connected to the home’s exterior wall;
  • Directly on a concrete or composite pad;
  • Atop a frame that sits on a pad.

The outdoor unit contains a compressor and fan, and each causes vibration. To accommodate this vibration, the outdoor unit is typically mounted on a structure that uses rubber dampers or one that isolates the outdoor unit from the house.

In areas where the ground is prone to frost-heave, installing the outdoor unit on a wall-mounted frame can be most practical. Mounting frames are attached to the structure, either with lag screws into wall studs or bolts anchored into concrete on a foundation wall. The size and weight of some outdoor units—multizone units might weigh about 300 pounds—may dictate a more robust mounting solution such as a stronger wall-mount or a ground stand.

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