Fujitsu line set sizes
Short answer: Every Fujitsu wall-mount from 9,000–12,000 BTU uses a 1/4" liquid × 3/8" gas line set. Above that, the series decides: 15k runs 1/4" × 3/8" or 1/4" × 1/2", 18k–24k runs 1/4" × 1/2" on standard series but jumps to 3/8" × 5/8" on the high-SEER RLXFW and Orion XLTH, and every 30k–36k takes 3/8" × 5/8". Fujitsu sizing shifts by series more than any other brand we track — find your model number in the series table below, then confirm in your manual.
The right line set diameter for your Fujitsu Halcyon or AIRSTAGE mini-split by capacity — plus why Fujitsu's sizes shift by series more than most brands, so the manual matters here. Prefer to size by run length too? Use the size calculator.
Fujitsu line set size by capacity
Line set diameter is set by your system's capacity and series. Match your Fujitsu unit's BTU rating to the typical liquid-and-gas pair below — but read the next section first, because Fujitsu's exact sizes vary by series more than the other brands.
| Fujitsu system size | Typical line set (liquid × gas) |
|---|---|
| 9,000 BTU | 1/4" × 3/8" |
| 12,000 BTU | 1/4" × 3/8" |
| 15,000 BTU | 1/4" × 3/8" or 1/4" × 1/2" (by series) |
| 18,000 BTU | 1/4" × 1/2" or 3/8" × 5/8" (by series) |
| 24,000 BTU | 1/4" × 1/2" or 3/8" × 5/8" (by series) |
| 30,000–36,000 BTU | 3/8" × 5/8" |
Found your size? Get the matching line set
We stock all three sizes Fujitsu wall-mounts use: 1/4" × 3/8" for every 9k–12k, 1/4" × 1/2" for most 15k–24k standard series, and 3/8" × 5/8" for the high-SEER 18k–24k and all 30k–36k units — in 16 ft and 25 ft, open for preorder.
Find your series: Fujitsu model number → line set size
Most Fujitsu owners know their model number — ASU12RLS3, AOUH24KZAH1, and so on. The letters between the capacity and the trailing digits name the series, and with Fujitsu the series decides the line set. Sizes below are taken from Fujitsu's own submittal sheets and line set guide.
| Series | 9k–12k | 15k | 18k–24k | 30k–36k | Refrigerant |
|---|---|---|---|---|---|
| RLF1 / RL2 / RLB — standard Halcyon | 1/4" × 3/8" | — | 1/4" × 1/2" | — | R-410A |
| RLS3 / RLS3H, LZAS1 / LZAH1 — high-SEER | 1/4" × 3/8" | 1/4" × 1/2" | — | — | R-410A |
| RLXFW1 / RLXFWH — high-SEER large | — | — | 3/8" × 5/8" | 3/8" × 5/8" (30RLXEH) | R-410A |
| 30RLXB / 36RLXB — entry large | — | — | — | 3/8" × 5/8" | R-410A |
| Altair 500 / 700 (KPAS1, KMAS1) | 1/4" × 3/8" | — | 1/4" × 1/2" (KPAS1) | 3/8" × 5/8" (KPAS1) | R-32 |
| Orion XLTH / XLTH+ (KZAH1, KTAP1) | 1/4" × 3/8" | 1/4" × 1/2" (KZAH1) · 1/4" × 3/8" (KTAP1) | 3/8" × 5/8" (KZAH1) | — | R-32 |
Two traps worth calling out. The 18k–24k high-SEER units (RLXFW, Orion XLTH) take a 3/8" liquid line — rare at that capacity, and the easiest Fujitsu sizing mistake to make; a standard-series 18k next to it uses 1/4" × 1/2". And at 15,000 BTU the gas line depends entirely on series — RLS3, LZAH1, and Orion XLTH run 1/2", while the Orion XLTH+ (15KTAP1) drops back to 3/8". Altair 300 (KNAS1) sizes above 12k aren't in Fujitsu's published guide — for those, go straight to the manual.
Fujitsu sizes vary by series — check your exact model
Fujitsu spreads a single capacity across several series, and the line set can differ between them. Because of that spread, don't size a Fujitsu by capacity alone — find your series in the table above, then read the connection pipe diameter line in your model's installation manual and match it exactly.
Field-flared, not quick-connect
Fujitsu mini-splits use standard field-flared line sets, not pre-charged quick-connect. You flare the copper ends and pull a vacuum to remove air and moisture before opening the service valves — work that typically needs a vacuum pump and EPA 608 certification. Shop standard line sets for a Fujitsu install, or see pre-charged line sets if you want the no-vacuum route on a compatible system.
Fujitsu line set length limits
Diameter is only half the spec. Your Fujitsu system also limits how long the line set can run and how far the indoor and outdoor units can sit apart in height — and Fujitsu splits sharply by capacity. Plan your run to the figures below, then confirm the exact limits for your model in its installation manual.
| Minimum line length | Maximum line length | Max vertical separation | Pre-charged for |
|---|---|---|---|
| 10–16 ft by capacity | 66–165 ft by capacity | 49–98 ft by capacity | 49–66 ft by capacity |
The split is large. Fujitsu's small Halcyon units (9,000–15,000 BTU) top out around 66 ft of line with up to 49 ft of vertical separation, while 18,000 BTU and larger units jump to about 165 ft with up to 98 ft of lift. The factory charge covers roughly the first 49 ft on small units and 65–66 ft on larger ones; beyond that an HVAC pro adds about 0.22–0.43 oz per extra foot. Minimum run is about 10 ft on small units and 16 ft on 18k and up.
Stocked lengths, multi-zone, and refrigerant
Because Fujitsu uses standard line sets, you size to your run — common stocked lengths are 15, 25, 35, and 50 ft. On multi-zone Halcyon systems a branch box splits the runs: a larger trunk (often 3/8" liquid) feeds the branch box, and each indoor unit drops to its own smaller line set. Size every run to its own head.
Match the refrigerant. Legacy Fujitsu Halcyon units use R-410A — and here Fujitsu took a different road than most brands in the 2026 transition: its new AIRSTAGE wall-mounts (the Altair and Orion series) run R-32, not the R-454B that Mitsubishi, Daikin, and most US competitors chose. Both are A2L refrigerants, and the copper line set is the same either way — but your tools, gauges, and any added charge must match your system's refrigerant.
How to find your Fujitsu model's line set size
- Identify the indoor and outdoor model numbers. Note the series (RLS, RLXFW, AIRSTAGE, etc.) and capacity — with Fujitsu, the series matters as much as the BTU.
- Check the installation manual's connection pipe diameter. It lists the exact liquid and gas sizes, the maximum line length, and the refrigerant for your specific model — the final word.
Common questions
What size line set does a Fujitsu 12,000 BTU use?
Most Fujitsu Halcyon 12,000 BTU single-zone units use a 1/4" liquid line with a 3/8" gas line, and every 9,000 BTU model uses the same pair. At 15,000 BTU it depends on series — RLS3-class and Orion XLTH units step the gas line up to 1/2". Confirm against your specific model's installation manual.
Do Fujitsu line set sizes vary by series?
Yes, more than most brands. An 18,000 BTU Fujitsu uses 1/4" × 1/2" on standard series but 3/8" × 5/8" on the high-SEER RLXFW and Orion XLTH units. Always match the exact liquid and gas sizes in your model's installation manual rather than assuming by capacity alone.
Do Fujitsu mini-splits use quick-connect or flared line sets?
Fujitsu uses standard field-flared line sets, not pre-charged quick-connect. You flare the copper and pull a vacuum before opening the service valves, so a Fujitsu install needs a vacuum pump and typically EPA 608 certification — unlike a pre-charged DIY system such as MRCOOL.
What refrigerant do Fujitsu mini-splits use?
Legacy Fujitsu Halcyon units use R-410A. Fujitsu's newer AIRSTAGE wall-mounts — the Altair and Orion series — use R-32, unlike most US brands, which moved to R-454B in the 2026 transition. Match your line set, tools, and any added charge to your unit's refrigerant.
What is the minimum line set length for a Fujitsu mini-split?
Fujitsu specifies a minimum line set length of about 10 feet (3 m) on its 9,000–15,000 BTU Halcyon units and about 16 feet (5 m) on 18,000 BTU and larger models, to limit noise and ensure proper oil return. Confirm the figure in your model's manual.
What is the maximum line set length for a Fujitsu mini-split?
It depends sharply on capacity. Fujitsu's 9,000–15,000 BTU Halcyon units allow about 66 ft of line, while 18,000 BTU and larger units jump to about 165 ft, with 49–98 ft of vertical separation. The factory charge covers roughly 49–66 ft; beyond that an HVAC pro adds refrigerant. Confirm your unit's maximum in its manual.
Line set sizes for other brands: Mitsubishi · Daikin · LG · MRCOOL · Pioneer
This page provides general guidance on Fujitsu mini-split line set sizing based on published Fujitsu specifications. Exact line diameters vary by series and model, and lengths, maximum line length, and refrigerant (R-410A or R-454B) differ by unit — always verify against your unit's official installation manual before purchasing or installing.