Refrigerant Line Sizing Chart
Typical suction (vapor) and liquid line copper sizes by system tonnage for R-410A, for short runs. These are starting points — real line sizing depends on the total equivalent length, the vertical rise, and the manufacturer’s chart. The liquid line stays small; the suction line does the heavy lifting and grows with capacity and run length.
Typical line sizes by tonnage (R-410A)
| Capacity | Suction line OD | Liquid line OD |
|---|---|---|
| 1.5 ton | 5/8" (some 3/4") | 1/4"–3/8" |
| 2 ton | 5/8"–3/4" | 3/8" |
| 2.5 ton | 3/4" | 3/8" |
| 3 ton | 3/4"–7/8" | 3/8" |
| 3.5 ton | 7/8" | 3/8" |
| 4 ton | 7/8" (1" if run > 75 ft) | 3/8" |
| 5 ton | 7/8"–1-1/8" | 3/8" (occasionally 1/2") |
Two lines, two jobs
The two lines are sized for opposite reasons. The liquid line carries dense high-pressure liquid, so it stays small — often just 3/8" even on a 5-ton system — and on residential equipment it is deliberately held small to avoid adding refrigerant charge that a big liquid line would hold. The suction line carries low-density vapor back to the compressor, and its whole job is to keep that vapor moving fast enough to sweep oil along with it. That velocity requirement is why the suction line is always the larger of the two and why it grows with both capacity and run length.
Because velocity is the constraint, length matters as much as tonnage. A short run uses the sizes above; a long run upsizes the suction line to hold pressure drop down, but not so far that velocity falls below what carries oil — which is exactly why two-stage and variable-capacity systems are sized at their reduced capacity. For total capacity itself, the cooling tonnage calculator gets you the tons to start from.
Common questions
What size refrigerant lines for a 3-ton system?
Typically 3/4" to 7/8" suction (vapor) line and 3/8" liquid line for a short R-410A run. But line sizing depends on the total equivalent length and vertical rise, not tonnage alone — the manufacturer’s line-size chart is authoritative, and longer runs upsize the suction line.
Why is the liquid line smaller than the suction line?
Because liquid is dense and vapor is not. A small liquid line carries the refrigerant mass with acceptable pressure drop, while the low-density suction vapor needs a much larger cross-section to keep its velocity high enough — roughly 800–1000 feet per minute — to carry oil back to the compressor. Undersize the suction line and oil gets trapped in the evaporator; oversize it and velocity drops too low for oil return.
Do long line sets need bigger pipe?
The suction line, usually yes — runs beyond about 50–75 feet typically go up one suction-line size to keep pressure drop and velocity in range, and long vertical lifts add their own rules. The liquid line is generally held at 3/8" on residential systems to avoid adding excess charge. Always use the manufacturer’s long-line-set guidelines for anything beyond a short run.
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