Refrigerant Line Set: Sizes, Length Limits, Reuse

Quick answer

A refrigerant line set is the pair of copper tubes that connects the outdoor unit of a split air conditioner or heat pump to the indoor coil: a larger insulated suction line and a smaller liquid line.

Its size, length, height difference and cleanliness all affect capacity, refrigerant charge and how long the compressor lasts.

Quick facts

The key facts about Refrigerant Line Set, with sources:

Two pipes: Suction (vapor) line, larger and insulated; liquid line, smaller ¹
Common residential liquid line: 3/8 inch, required on long runs in one maker's guide ¹
Factory charge covers: 15 feet of line set on that maker's R-410A units ¹
Long line threshold: Over 80 feet of actual length in Goodman's guideline ¹
Suction insulation: Typically 3/8 inch; 1/2 inch for long runs through hot spaces ¹
Who installs it: Licensed HVAC tech; EPA 608 rules apply to refrigerant work ²

Key takeaways

The line set carries refrigerant between the indoor and outdoor units.
Length is judged by "equivalent length," which counts bends, not just feet of pipe ¹.
Longer runs lose a little capacity and need extra refrigerant ¹.
Reusing an old line set can work, but size, condition and refrigerant compatibility must be checked.
Cut, brazed and evacuated only by a licensed technician.

What a line set is

Look at the outdoor unit and you will see two copper pipes leaving it and heading into the wall. That pair is the line set.

The fat one, wrapped in black foam, is the suction line. It carries cool refrigerant vapor back to the compressor. The thin one is the liquid line. It carries warm liquid refrigerant to the indoor coil.

The foam on the suction line keeps it from picking up heat and from sweating. Goodman notes most tubing kits come with 3/8-inch insulation on the suction line, and calls for thicker 1/2-inch insulation on long runs through hot areas ¹.

Line sets come in pre-cut kits with flared or plain ends, or as coils of copper cut on site. Inside the house they run through walls, attics, crawlspaces or chases. A low-voltage control wire usually runs alongside.

What each pipe carries

Outdoor unit → liquid line (small) → metering device → indoor coil
Indoor coil → suction line (large, insulated) → compressor
On a heat pump in winter, flow reverses, and the large line carries hot gas indoors

Why size and length matter

Refrigerant loses pressure as it travels, like water in a long garden hose.
Pressure loss in the suction line lowers capacity. A larger suction line loses less ¹.
Oil travels with the refrigerant and must make it back to the compressor, especially on vertical rises.
Extra pipe holds extra refrigerant, so the charge must be adjusted ¹.
A liquid line that is too large adds a lot of refrigerant. Goodman limits long residential runs to 3/8 inch because a bigger charge "could possibly shorten a compressor's life-span" ¹.

Line set types and parts

Type or part	What it is	Notes
Pre-charged / pre-flared kit	Factory-cut set, common with mini-splits	Fixed lengths; flare joints must be made to torque
Field-cut copper	Soft copper from a coil, cut and brazed on site	Most central systems
Suction line	Larger, insulated vapor line	Size chosen for capacity and oil return
Liquid line	Smaller line	Size limited to control charge
Line set cover	Plastic channel on the outside wall	Protects pipes and insulation from sun and damage

Worked example: equivalent length, capacity and charge

This uses the method and tables in Goodman's TP-107 long line set guideline (September 2020) for a 3-ton (36,000 BTU/h) R-410A system with a 3/4-inch suction line and 3/8-inch liquid line ¹.

Step	Math	Result
Straight pipe	Measured run	150 ft
Four 90° short-radius elbows, 3/4 in.	4 × 1.7 ft ¹	6.8 ft
Two 90° long-radius elbows, 3/4 in.	2 × 1.5 ft ¹	3.0 ft
Equivalent length	150 + 6.8 + 3.0	159.8 ft
Capacity multiplier, 36,000 BTU/h, 3/4 in. suction, about 150–175 ft	Table 5-3 ¹	0.98 to 0.97
Usable capacity	36,000 × 0.98	About 35,280 BTU/h
Same run with a 5/8 in. suction line	36,000 × 0.93 ¹	About 33,480 BTU/h
Extra refrigerant to start	(150 − 15) × 0.6 oz/ft ¹	81 oz, then final charge by subcooling

A correction worth knowing: Goodman's own worked example in the same guideline uses these exact elbows and prints "150 + 3.4 + 3 = 156.4 equivalent feet." Four elbows at 1.7 feet each is 6.8 feet, so the right total is 159.8 feet.

The guide's metric note also lists 17.0 g per meter beside 0.6 oz per foot, while its formula uses 55.8 g/m, which is the correct conversion. Small slips like these are why a tech should run the math, not copy it.

Where you will see the term

On a replacement quote: "reuse existing line set," "flush line set," or "new line set."
In the outdoor unit's installation manual: allowed sizes, lengths and lift.
On mini-split quotes: line set length per head and any extra charge.
In inspection notes: damaged insulation, kinks, or lines touching the structure.

Reuse or replace the line set?

Reasons reuse can work

Lines buried in finished walls are hard to reach.
Sound, correctly sized copper can be cleaned and reused if the maker allows it.
Less disruption to the home.

Reasons to replace

Wrong size for the new unit's capacity or rules.
Kinks, corrosion, damaged insulation or leaks.
Contamination after a compressor burnout.
Old oil or refrigerant residue may not suit the new refrigerant and oil.

Length and lift limits

Every outdoor unit has limits on line length and on how far the outdoor unit can sit above or below the indoor coil. In Goodman's guideline, the maximum equivalent length is 250 feet for single-stage units with scroll or reciprocating compressors, and 150 feet for rotary and two-stage units ¹.

Long runs bring extra rules: a crankcase heater, a hard start kit and a TXV are all required in that guideline, and the unit must be charged to 7–9°F subcooling at the indoor unit ¹. Other makers and other models set different numbers, so the manual for your exact unit governs.

Getting the charge right matters more on a long run. DOE's review of field studies found undercharge in 29% to 78% of systems tested and overcharge in 4% to 50% ⁵.

Sources: [1]

Cost drivers

HyreHVAC lists no prices without enough dated quotes. What drives line set cost: total length, pipe sizes, access (finished walls, attics, two-story runs), insulation, wall penetrations and covers, brazing labor, flushing an old set, and extra refrigerant for long runs.

A new outdoor unit with a reused line set may cost less up front, but a leak or contamination found later can cost more. Ask the installer what checks they will do before reuse. See the replacement calculator for what moves a system price.

How a line set is installed

Licensed HVAC work. The refrigerant steps require EPA Section 608 certification ².

Plan the route, keep bends gentle, and size the lines from the outdoor unit's manual.
Sleeve lines through walls; they must not rub on framing. Goodman shows isolators and sleeves to stop vibration noise ¹.
Support the lines at intervals. The guideline shows suction-line straps at 8-foot intervals on joists or rafters ¹.
Braze joints with a nitrogen purge, or make flares to torque on mini-splits.
Pressure test with nitrogen, then pull a deep vacuum.
Add refrigerant for the extra length, then set the final charge.
Seal wall openings and cover exposed insulation from sunlight.

Looking after it

You: look at the foam on the suction line outside. Torn or sun-cracked foam can be reported at the next tune-up.
You: keep string trimmers, pets and ladders away from the lines.
You: note any ice on the lines in cooling mode and turn the system off.
Tech: replace damaged insulation and check that lines do not touch the house.
Tech: check for oil spots at fittings, a sign of a leak.

Warning signs and when to call a pro

Ice on the suction line. See frozen evaporator coil.
Oily residue at a joint or service valve.
A kinked or crushed section.
Water dripping from the insulated line inside a wall or ceiling.
Banging or buzzing pipes when the system starts.

Rules that apply

Section 608. EPA's rules under 40 CFR Part 82, Subpart F prohibit venting refrigerant while servicing or disposing of equipment ². Recovery comes before any line set work on a charged system.

New refrigerants. New residential systems with parts made after January 1, 2025 must use a refrigerant under a 700 GWP limit ³. EPA says the rule applies to new systems, not ones already installed ⁴.

When you replace an R-410A system with an R-454B or R-32 system, ask whether the existing line set meets the new unit's size and cleanliness rules. See our refrigerant transition research.

Codes. Wall penetrations, protection and access follow your local mechanical code. Adoption varies.

Sources: [2] [3] [4]

Line set vs related terms

Term	Relationship
Line set	Pipes that join the indoor and outdoor units
Ductwork	Carries air, not refrigerant
Condensate drain line	Plastic pipe for water from the coil; often runs nearby
Service valves	Valves on the outdoor unit where the line set connects

Common misconceptions

Myth Any old line set is fine for a new system.: Reality Size, condition and the new unit's rules decide. Check the manual.
Myth Extra pipe can be coiled up behind the unit.: Reality Excess length adds pressure loss and charge. Cut to length where the maker allows.
Myth Line length only means feet of pipe.: Reality Bends add equivalent length ¹.
Myth Insulation is cosmetic.: Reality Bare suction lines lose capacity and drip water.

Climate and routing

In hot states, line sets often run through attics that get far hotter than outdoor air, which is where Goodman calls for thicker suction insulation and liquid-line insulation ¹. In humid climates, unbroken insulation keeps lines from sweating onto ceilings. Your state page lists climate notes.

When it matters to you

It matters on every replacement and every new mini-split. Ask three questions: will the line set be reused or replaced, does its size meet the new unit's manual, and how much refrigerant will be added for the length?

Next step: compare quotes line by line with the quote comparison tool, and ask for a vacuum reading in microns at startup.

Related guides

Questions about Refrigerant Line Set

What is a line set on an AC unit?

It is the pair of copper pipes running between the outdoor unit and the indoor coil. The larger, insulated suction line carries vapor back to the compressor. The smaller liquid line carries liquid refrigerant to the indoor coil.

Can I reuse my old line set with a new AC?

Often, if it is the right size for the new unit, undamaged and clean. Many installers flush or test it first. After a compressor burnout, or when sizes do not match the new unit's manual, replacement is safer. Ask the installer how they will check it.

How long can a refrigerant line set be?

It depends on the outdoor unit. In one Goodman guideline, runs over 80 feet are "long line" installs with extra requirements, and the maximum equivalent length ranges from 150 to 250 feet by compressor type. Always use the manual for your exact model.

Why does the big copper line have insulation?

The suction line carries cold vapor. Insulation stops it from picking up heat, which would cut capacity, and stops it from sweating water onto walls or ceilings. Damaged insulation should be replaced.

Does a longer line set need more refrigerant?

Yes. Goodman's R-410A units come charged for 15 feet. For longer runs, its guideline adds about 0.6 ounces per foot of 3/8-inch liquid line as a starting point, then sets the final charge by subcooling.

Why is there ice on my AC line?

Ice on the suction line usually means low airflow from a dirty filter or blocked return, or low refrigerant from a leak. Turn cooling off, run the fan to thaw the coil, change the filter, and call a technician if it returns.

What is equivalent length?

It is the straight length of pipe plus an allowance for each bend, because bends add pressure loss. In Goodman's table a 3/4-inch short-radius 90° elbow adds 1.7 feet. Installers use equivalent length to check limits and capacity loss.

Do mini-splits use line sets too?

Yes. Each indoor head connects to the outdoor unit with its own line set, usually with flare fittings. Mini-split makers set minimum and maximum lengths per head, and extra length often means added refrigerant.

Sources

Goodman, TP-107 Long Line Set Application Guideline, R-410A (September 2020), retrieved October 10, 2026.
U.S. EPA, Stationary Refrigeration and Air Conditioning (Section 608), retrieved October 10, 2026.
U.S. EPA, Technology Transitions HFC Restrictions by Sector, retrieved October 10, 2026.
U.S. EPA, Frequent Questions on the Phasedown of Hydrofluorocarbons, retrieved October 10, 2026.
U.S. DOE Building Technologies Office, Residential HVAC Installation Practices: A Review of Research Findings (June 2018), retrieved October 10, 2026.

Expert review

Written by the HyreHVAC Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.

How the numbers were checked: Every length, size, multiplier and charge figure is read from Goodman TP-107 (Sept. 2020), downloaded 10 October 2026. The worked example recomputes the guideline's own elbow example and flags its arithmetic slip; capacity multipliers are read from Table 5-3, not interpolated.

Suggest a correction. We fix errors and say what changed.