TradesHow this works
For a given tonnage, there is a typical liquid and suction line size at a standard run length. This tool starts there, then adjusts for the two things that actually change it: a long run, which pushes the suction up a size to hold pressure drop, and vertical lift, which raises oil return and subcooling concerns. It flags when you are past the standard length and into the manufacturer long-line rules.
These are typical R-410A values for planning. The condenser installation manual is the final word on size, added charge, and whether the run needs traps.
Common questions
Why does line length change the suction size but not the liquid size?
The suction line carries low-pressure vapor, so a long run costs pressure and capacity, and upsizing it protects the system. The liquid line carries dense high-pressure liquid where a bigger pipe just adds refrigerant charge with no benefit, so it stays the same.
What counts toward equivalent length?
Straight tubing plus an allowance for every elbow and fitting, plus the vertical rise. A run with several bends is longer than the tape measure says, which is why the equivalent length is what drives the size, not the straight distance.
Why does the manual override this tool?
Line sizing, added charge, and whether you need oil traps all depend on the specific condenser. Manufacturers publish long-line-set application charts for their equipment. This tool is a fast planning starting point, not a substitute for that chart.
Sources: Typical R-410A residential line-set charts; manufacturer long-line-set application guides (authoritative). Engine version 1.0.0. Risk tier 2.