Refrigerant Line Size Calculator
Get a typical suction and liquid line size for a split AC or heat pump by tonnage, with a note on long line-set runs.
How it works
Line size looked up from nominal tonnage (BTU/hr ÷ 12,000) using typical R-410A OD sizes · long runs may need a size change per manufacturer data
Refrigerant line sets have two pipes: a larger insulated suction (vapor) line and a smaller liquid line, sized by system capacity to keep refrigerant velocity high enough to carry oil back to the compressor without adding excess pressure drop. The sizes here are the common defaults for R-410A residential equipment. Always confirm against the specific unit’s installation manual — and for line sets longer than about 50 feet or with a big height difference, the manufacturer often specifies a different size, extra oil, or a trap.
Worked example
A 36,000 BTU/hr system is 3.0 tons, which typically uses a 7/8-inch suction line and a 3/8-inch liquid line. At a 25 ft run that is a standard installation; beyond 50 ft you would check the manufacturer’s long-line-set chart.
Frequently asked questions
Why is the suction line bigger than the liquid line?
The suction line carries low-pressure refrigerant vapor, which is far less dense than the liquid, so it needs a larger diameter to keep pressure drop low. The liquid line carries dense high-pressure liquid and can be much smaller.
Do these sizes always match my unit?
They are typical defaults, not a substitute for the manufacturer’s spec. The installation manual lists the exact suction and liquid line sizes for each model and gives corrections for long or vertical runs — always follow it.
What changes on a long line set?
Longer runs add pressure drop and make oil return harder. Manufacturers may call for a larger suction line, extra refrigerant charge, added compressor oil, or traps on vertical risers beyond a certain length.
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This calculator is for educational purposes. Double-check important results before acting on them.