How to Install and Insulate a New Line Set

Why this matters

The line set is the part of a split system the customer never looks at and the part that decides whether the system lasts. A kinked suction line is a permanent restriction that no charge adjustment fixes. A line rubbing on a joist wears through in a few seasons and dumps the charge. An uninsulated stretch of suction line in an attic sweats onto drywall all summer, and insulation left bare in the sun outdoors crumbles in two or three years and starts eating capacity and dripping on the siding.

None of that shows up at start-up. The system charges, the customer signs, and the defect waits. Running and insulating the set correctly is the cheapest quality control on the whole install, because it is done once with the walls and the attic open.

What this covers, and where it hands off

This is routing, bending, supporting and insulating a new soft-copper line set between an air handler or coil and an outdoor unit, through the point where the stubs are ready to braze or flare. Line sizes, maximum length, lift and added charge come from the maker's table and belong to Line Set Sizing, Length and Lift Field Card. The wall penetration itself is How to Run a Line Set or Cable Through an Exterior Wall. Joining is Brazing With a Nitrogen Purge Standard or, for mini-splits, How to Make and Torque a Flare on a Mini-Split Line Set. Proof that it holds is How to Run a Standing Nitrogen Pressure Test on a New Line Set, and Evacuation and Vacuum Decay Verification.

Start state

• Sizes and length confirmed against the maker's table for this outdoor model and indoor coil. Buy and cut from the table, not from what the last job used.
• The route walked from indoor stubs to outdoor service valves, with a tape, before any copper comes off the truck. You are looking for the shortest path that stays out of the way of future work, keeps out of walking paths in the attic, and never crosses a bath fan, a flue or a can light.
• Both ends of the copper capped and kept capped until the moment of joining. A coil that sat open in the van picked up moisture and dirt you will be pulling out with a vacuum pump later.
• Attic or crawlspace hazards checked first. In an attic: walk on framing or boards only, watch for exposed nails through the roof deck at head height, and know where the electrical runs are before you drill or staple. In hot weather the attic sets the work schedule; mornings, water, and a second person within call. Anyone who feels dizzy or stops sweating comes down.

The route, as built

      ATTIC, air handler horizontal
 [AH] stubs
  |  |
  +--+== lines on top of a joist, =======+
     cushion clamps 6 ft max apart,      |
     suction insulated, seams glued      |
                                         | bend with a
                                         | bender, no knee
                                         |
                                         | vertical drop in
                                         | chase, support at
                                         | top and bottom
   exterior wall                         |
   ---+----+                             |
      |sleeve  <-------------------------+ bend through rim
      |sealed
   ---+-+--+  both faces of the wall
        |
        +---- along wall, UV jacket or line cover,
              insulation butted and glued at joints
                           |
                    [OUTDOOR UNIT] service valves

Steps, each with what it prevents

1. Uncoil by rolling, not pulling. Stand the coil on edge and roll it along the floor or the attic boards while a helper holds the free end down. Pulling the end straight off a coil like a spring twists the tube and puts a spiral in it that becomes a flat spot the first time you bend near it. Leave a little extra at each end for the final fit; you cut to length after the run is set.

2. Bend with a bender sized to the tube. A lever bender with a shoe for each OD, or spring benders on the small sizes, keeps the tube round through the bend. A hand bend over a knee or around a joist works on 3/8 liquid line and flattens a 7/8 suction line, and a flattened suction bend is a restriction that raises the pressure drop exactly where you cannot see it. Bend the suction line first, then shape the liquid line to follow it. Never bend the same spot twice: copper work-hardens and the second bend kinks.

3. Lay the route so the lines are never the support for anything else. Run on top of joists or along the side of a truss, not across open bays where someone will step on them. Keep at least a hand's width from flues and vent connectors; elastomeric insulation is not rated for flue temperatures. Where the lines must cross a walking path, sleeve or board over them.

4. Support at or inside the code spacing. IMC Table 305.4, as adopted by your jurisdiction, sets maximum support spacing for copper tube 1-1/4 inch and smaller at 6 feet horizontal and 10 feet vertical in the 2021 edition; check your adopted edition. Use clamps or hangers that grip over the insulation without crushing it, or cushion clamps with a rubber liner, and keep bare copper away from steel straps, sheet metal and framing nails. Copper on steel in a damp attic corrodes, and copper on a vibrating sheet-metal edge wears through. A sagging suction line also sags its insulation open at the seams, which is a condensation path.

5. Isolate from the structure where noise travels. A line strapped tight to a bedroom ceiling joist carries compressor pulsation straight into the room. Rubber-lined clamps and a gentle loop near the outdoor unit, not a rigid straight shot, cut that down.

6. Pass the wall through a sleeve, sealed both sides. The penetration, sleeve sizing and flashing are covered in How to Run a Line Set or Cable Through an Exterior Wall. What matters here: the insulation stays continuous through the sleeve, so size the sleeve for the insulated line, and seal both ends against air and water with a sealant compatible with the insulation.

7. Insulate the suction line completely and seal every seam. IRC M1411.6, as adopted, requires suction (vapor) line piping and fittings to be insulated to at least R-4 with a low-permeance surface in the editions that carry it; check yours, and check the R-value printed on the sleeve, since some economy pre-insulated sets come in under it. On pre-insulated sets, every factory seam that was cut or opened is glued with the insulation maker's contact adhesive, and every butt joint is glued and then wrapped with the maker's tape. Duct tape and electrical tape let go in an attic summer.

Insulate the liquid line too where the maker calls for it. Most mini-split makers require both lines insulated, and many heat pump instructions require it on runs through unconditioned space because the liquid line carries warm liquid from the indoor coil in heating mode and loses that heat to a cold attic.

8. Keep insulation clear of the braze zone, then close it after. Slide the insulation back several inches from each joint before brazing and protect it with a wet rag or heat barrier; elastomeric foam that touches a torch chars and gives off irritating smoke, so if it does catch, step back and let the air clear before continuing. After the joint cools and the pressure test passes, butt the insulation back to the fitting and glue it. An open inch at each braze joint at the air handler is where the sweating starts.

9. Protect outdoor insulation from sunlight and damage. The residential energy code, as adopted, requires piping insulation exposed to weather to be protected from sunlight, moisture and damage; check your adopted edition for the exact wording. A UV-rated jacket, a line-set cover, or a coating the insulation maker approves for outdoor use all satisfy it. Bare black foam on a south wall is the failure everyone has seen: chalky, split, and falling off by the third summer.

Worked example: a 3-ton heat pump, attic air handler

A new 3-ton R-410A heat pump. Air handler horizontal in the attic, outdoor unit on a pad on the side of the house. Using the line-set card's illustrative table, 3/8 inch liquid and 7/8 inch suction, both to be insulated because the maker's heat pump instructions require it for runs through the attic.

The measured route. 22 feet along the top of a joist from the air handler to the gable wall chase, a 9 foot vertical drop inside the chase, out through the rim, then 7 feet along the outside wall to the service valves. Total 22 + 9 + 7 = 38 feet of tube. The pre-insulated coil is 50 feet, so 12 feet comes off the far end after the set is placed.

Supports, attic run. 22 feet at a 6 foot maximum is 22 / 6 = 3.7 spans, which rounds up to 4 spans, so 3 intermediate supports plus one at each end of the attic run. The crew set them at about 5 feet 6 inches apart, inside the limit, with rubber-lined clamps over the insulation.

Supports, vertical drop. 9 feet is under the 10 foot vertical maximum, so one support at the top of the drop and one at the bottom where it turns out through the rim is enough.

Outdoor run. 7 feet along the siding, one strap at the midpoint and one near the unit, with a short gentle loop before the service valves instead of a dead-straight run, so pulsation does not walk up the wall.

Bends. Four bends on the suction line: two at the top and bottom of the drop (the bottom one turns it out through the rim), one outside where the run turns along the siding, one at the service valve. Each made with the 7/8 shoe on the lever bender. The crew checked each with a quick eye along the tube: round, no ripples on the inside of the bend.

Insulation. The factory sleeve is printed R-4.2 on the suction line, which clears the R-4 minimum. Four joints to close after brazing (two at the air handler, two at the outdoor valves) plus one cut where the crew trimmed the slit to pass a strap: five glued joints in all. Outdoors, a line-set cover from the rim to the unit.

What a skipped step would have cost here. The first bend at the top of the chase is the one a crew is tempted to make by hand, kneeling on a joist. A flattened 7/8 bend there would sit in the dark behind a wall for the life of the system, read at the outdoor service valve as low suction pressure and high superheat, which looks like a short charge, and send the next tech hunting charge.

Finish test

• Every bend round. Sight along the tube; a flat or a ripple on the inside of the bend gets cut out before brazing, not after.
• Supports counted against the spacing you wrote down, and no bare copper touching metal or framing anywhere along the run.
• Insulation continuous from the air handler fitting to the outdoor service valve on every insulated line, all seams and butt joints glued, no gaps at the braze joints after the pressure test.
• Sleeve sealed on both faces of the wall.
• Outdoor insulation covered from the wall to the unit.

Walk the whole run with a flashlight once more after start-up on a humid day. Any sweat on the outside of the insulation is an open seam or insulation too thin for that space.

References

• IMC Table 305.4, support spacing for copper tubing, as adopted by your jurisdiction (2021 edition values cited)
• IRC M1411.6, insulation of refrigerant suction piping, as adopted by your jurisdiction
• Outdoor and indoor unit installation instructions; insulation manufacturer's instructions for adhesive, tape and outdoor protection
• See related: Line Set Sizing, Length and Lift Field Card; How to Run a Line Set or Cable Through an Exterior Wall
• See related: Brazing With a Nitrogen Purge Standard; How to Run a Standing Nitrogen Pressure Test on a New Line Set