HVAC Calculator
A2L Line Set Calculator: Sizing & Reuse Verdict
Size the liquid and suction lines for R-454B, R-32, or R-410A by tonnage and length, then get a clear REUSE, FLUSH & REUSE, or REPLACE verdict for an existing R-410A set, with the charge adjustment and a printable checklist. Every number cites its manufacturer source.
By refrigerant
Line Set Size by Tonnage and Length
Suction (vapor) and liquid line OD for residential 1.5 to 5 ton split systems. The suction line steps up one size past about 25 feet to hold velocity and control pressure drop; the liquid line stays the same. R-454B and R-410A share these sizes; R-32 uses the same table but needs a velocity check when reusing R-410A tubing.
| Tonnage | ≤ 24 ft (Suct / Liq) | 25–49 ft | 50–79 ft |
|---|---|---|---|
| 1.5 ton | 5/8" / 1/4" | 3/4" / 3/8" | 3/4" / 3/8" |
| 2 ton | 5/8" / 1/4" | 3/4" / 3/8" | 3/4" / 3/8" |
| 2.5 ton | 5/8" / 1/4" | 3/4" / 3/8" | 3/4" / 3/8" |
| 3 ton | 3/4" / 3/8" | 7/8" / 3/8" | 7/8" / 3/8" |
| 3.5 ton | 7/8" / 3/8" | 1-1/8" / 3/8" | 1-1/8" / 3/8" |
| 4 ton | 7/8" / 3/8" | 1-1/8" / 3/8" | 1-1/8" / 3/8" |
| 5 ton | 7/8" / 3/8" | 1-1/8" / 3/8" | 1-1/8" / 3/8" |
Past 79 feet or 50 feet of vertical rise, the residential table defers to the manufacturer long-line guide (Carrier LLG-R454B-01 allows up to a 250 ft equivalent length). Carrier also permits 1/4 and 5/16 inch liquid lines on small tonnages with a TXV; always confirm against the guide that ships with the unit.
Charge Adjustment per Foot of Line Set
Both systems ship pre-charged for 15 feet of line set. Add or remove refrigerant for the actual run. For R-454B, Carrier keys the adder to the liquid line diameter and subtracts the 9 oz factory charge: adjustment = oz/ft × total length − 9 oz.
| Liquid Line OD | R-454B Charge (oz/ft) |
|---|---|
| 3/8" | 0.60 |
| 5/16" | 0.40 |
| 1/4" | 0.27 |
R-32 is charged by the suction-and-liquid combination beyond the 15 ft base (0.23 to 0.64 oz/ft, Goodman IOG-4047, p.9). The calculator applies the right per-refrigerant formula automatically and shows the math.
Reusing an R-410A Line Set: the Real Rules
Oil is not the problem (unless you are coming from R-22)
The biggest myth in the A2L transition is that switching an R-410A set to R-454B needs a mineral-oil-to-POE flush. It does not. R-410A and R-454B both run on POE oil, so there is no oil incompatibility. Carrier states plainly that line sets can be reused because R-454B uses the same POE oil as R-410A. The mineral-oil-to-POE flush only matters when the existing set held R-22, which ran on mineral oil. Coming from R-22, the flush is mandatory before you put any POE refrigerant through the copper.
Flush for cleanliness, not compatibility
Even when oil is not the issue, flushing an R-410A set before reusing it with R-454B is the recommended best practice. Bosch's A2L change guide calls for flushing and a complete dry-nitrogen purge to clear residual oil, debris, and old refrigerant. Carrier does not require it from a system standpoint. The honest framing: flushing is a cleanliness step that most manufacturers recommend and none forbid, so this tool defaults to FLUSH & REUSE for a cross-refrigerant changeover and notes that straight reuse is defensible.
Pressure ratings carry over
R-454B was engineered to sit inside R-410A's pressure envelope. Operating pressures differ by only about 5% across the service range, well within any copper line set's rating, so tubing rated for R-410A is pressure-adequate for R-454B. What does need to be rated for the higher A2L working pressure is the new liquid-line filter-drier: use one rated at least 600 psig, and never reuse the old drier.
When you must replace
Replace the line set when it is undersized for the new tonnage and length, when the copper shows kinks, corrosion, pitting, or an active leak, or when the run exceeds the new unit's maximum length or vertical rise. Undersized lines cause pressure drop and starve the system; damaged lines cannot be verified clean and leak-free; over-length runs void the sizing and charge assumptions. Everything else is a candidate for reuse after the checklist steps.
Worked Example: 3 Ton R-410A to R-454B Changeout
Given: A 3 ton condenser is failing. You are installing an R-454B system and want to keep the existing R-410A line set: 35 ft total run, 8 ft of vertical rise, two 90 degree elbows, measured at 7/8 inch suction and 3/8 inch liquid, no visible damage.
Step 1: Size. A 3 ton system at 35 ft needs 7/8 inch suction and 3/8 inch liquid (the 25 to 49 ft band). The existing 7/8 / 3/8 set matches exactly.
Step 2: Charge. On 3/8 inch liquid, R-454B adds 0.60 oz/ft: 0.60 × 35 − 9 = +12 oz beyond the nameplate charge.
Step 3: Verdict. Sizes match, copper is sound, both use POE oil: FLUSH & REUSE. Flush and dry-nitrogen purge, fit a new 600+ psig filter-drier, pressure-test to ~150 psig, evacuate to 500 microns, then weigh in the nameplate charge plus 12 oz.
Result: The R-410A line set stays in the wall. No mineral-oil flush was needed because it never held R-22, and the diameters already matched the new system.
Frequently Asked Questions
Can I reuse my R-410A line set with R-454B?
Usually yes. Reuse an R-410A line set with R-454B if the liquid and suction diameters match what the new system needs, the copper is sound and leak-free, and you flush it, install a new filter-drier rated at least 600 psig, pull a vacuum to 500 microns or lower, and charge by weight. Both refrigerants use POE oil, so there is no oil-incompatibility that forces replacement, and R-454B runs within about 5% of R-410A pressures, so R-410A-rated copper is pressure-adequate.
What size line set for a 3 ton R-454B system?
A 3 ton system uses a 3/4 inch suction line and a 3/8 inch liquid line up to about 25 feet, and steps the suction up to 7/8 inch past 25 feet to hold velocity. The liquid line stays 3/8 inch. These are the residential sizes from the Goodman/Daikin R-32 tubing table, which the A2L systems share with R-410A.
Do I need to flush the line set when switching to R-454B?
Flushing is the recommended best practice, but it is not an oil-incompatibility mandate. R-410A and R-454B both use POE oil, so unlike an R-22 changeover there is no mineral-oil-to-POE conflict. Carrier states the line set can be reused without replacement; Bosch recommends flushing and a dry-nitrogen purge for cleanliness. Coming from R-22 (mineral oil), a flush is mandatory before reusing with any POE refrigerant.
Does R-454B need a bigger line set than R-410A?
No. R-454B uses the same liquid and suction diameters as R-410A for a given tonnage and run length, because their densities and pressures are close. That is why an R-410A line set can be reused with R-454B when the sizes already match. R-32 is different: it moves less mass, so an R-410A-sized set should have its tube velocities checked before reuse.
What micron do you evacuate an A2L line set to?
500 microns or lower, held without the pressure rising, confirmed on a micron gauge. This is the target in the Lennox and Carrier R-454B installation manuals. Some technicians pull to 300 microns as a more conservative figure. Use a vacuum pump rated for A2L refrigerants.
Do I need new fittings and a new filter-drier for R-454B?
Always install a new liquid-line filter-drier rated at least 600 psig for A2L service; never reuse the old drier. For fittings, R-454B equipment ships with mechanical fittings and the manufacturer requires OEM-approved components and spark-proof, A2L-rated tools. The idea that every Schrader core and flare must be a special A2L part is a common online claim but is not a manufacturer mandate; replacing Schrader cores whenever the system is open is simply good practice.
Can I reuse an R-410A line set with R-32?
With caution. R-32 uses POE oil like R-410A, so oil is not the issue, but R-32 moves less mass and runs lower velocities in the same tube. Goodman's R-32 guidance says not to reuse existing R-410A tubing without evaluating tube velocities across the operating range. If the diameters match the R-32 table and velocities check out, flush and reuse it with a new drier, leak test, and evacuation.
Related Calculators
Superheat & Subcooling Calculator
Charge by subcooling once the line set is in, with a four-quadrant diagnostic and R-454B cold-weather weigh-in guidance.
A2L Charge Limit Calculator
Maximum R-454B or R-32 charge for a room per UL 60335-2-40 and ASHRAE 15.2. A long line set adds charge, so check the limit.
EPA Refrigerant Leak Rate Calculator
Run the leak-rate math under 40 CFR 84.106 for systems 15 lb and up, effective January 1, 2026.
Line set is sorted. Now dial in the charge.
Once the set is flushed, evacuated, and weighed in, verify the charge by superheat and subcooling, and check whether the ambient is warm enough to trust the gauges.