Line set install guide

What Is a Line Set Rough-In Box?

It is a box set into the outside wall at rough-in, so the line set, condensate drain and low voltage wire leave the house through one finished opening instead of a hole and some foam.

Lineset Box set in wall sheathing with a coiled copper line set inside
Set at rough-in. The line set stays coiled inside until the condenser goes in.

The problem it solves

Every split system and mini-split needs at least one hole through the outside wall for the refrigerant lines, the drain and the control wire. Plumbers have washer boxes and electricians have junction boxes for the same reason: a defined place for the work to come through the wall. HVAC has usually had a drill bit and a can of foam.

That hole sits open from rough-in until start-up, which can be months. Three things tend to go wrong in that time:

  • The copper gets damaged. Framers, siders and landscapers all work around lines that are hanging out of the wall. One kink means rework.
  • The seal does not last. Foam packed around a rough hole shrinks and cracks, and that opens the wall to air, water and bugs.
  • It looks improvised. The termination is the one part of the HVAC job the homeowner sees every day.
Copper lines and PVC drain through a hole in sheathing packed with expanding foam
The usual way: a hole and some foam.

What the box does

  • Claims the spot. Once the box is in, the other trades work around it, the same way they work around an electrical box.
  • Protects the lines. Coil the line set inside the box until you set the condenser.
  • Gives the wall a real opening. The flange laps the sheathing, gets flashing tape, and the siding runs to it. You seal the holes you cut in the box, not a ragged hole in the wall.
  • Finishes clean. The lines leave the house through one molded opening in white or black.

How the Lineset Box™ installs

  1. Cut the opening. A 5-3/4 x 10-3/4 in rough opening in the sheathing, during rough-in.
  2. Set the box. The flange sits flat on the sheathing. The tapered end goes at the bottom.
  3. Fasten the flange. Eight 3/4 in galvanized deck screws or equal through the pre-drilled holes (not included).
  4. Tape and run your lines. Flashing tape on the flange. Hole-saw the flat top for the line set and drain, run the line set, drain and wire, and seal the holes with silicone.
Lineset Box flange finished into the siding
After the siding: the flange finishes into the wall.
Lineset Box line set rough-in box, black
Lineset Box™

One molded piece, white or black. 12.16 x 7.18 in flange, body 3.60 in deep behind it. UL-recognized polypropylene, UL 94 HB, UL File E130336. Patent pending, made in the USA.

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Outside wall vs. inside wall

A line set rough-in box handles the outside wall. On a ductless job there is a second spot: the stud bay behind the head unit, where the same lines need a protected place before the drywall closes. That is a mini-split rough-in box, and ours is the Star Box™.

Questions

When does a line set rough-in box go in?

At rough-in, as soon as the sheathing is on and before siding or the exterior finish.

What size opening does the Lineset Box need?

A 5-3/4 x 10-3/4 in rough opening in the wall sheathing. The body sits 3.60 in behind the flange, so it clears a 2x4 wall.

Does it come with knockouts?

No. You hole-saw the flat top on site to fit the job: 1-7/8 in for a 7/8 x 3/8 line set, 1 in for a 3/4 in PVC drain. Seal every hole with silicone.

Is this the same as a mini-split rough-in box?

No. The Lineset Box is for the outside wall, where the lines leave the house. Inside the wall behind the head unit, use a mini-split rough-in box such as the Star Box™.