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How long should each mini split line set be?
Short answer: Measure the path the line set will actually follow, through the wall, along it, up, over and down, not the straight distance between the two units. Add a couple of feet of slack at each end, then pick the next standard length up: 16, 25, 35 or 50 ft, or 66 and 75 ft with a coupler kit. MRCOOL line sets are pre-charged and can't be cut, so any extra gets coiled, and 75 ft is the most any one room can have.
Line set length is the measurement people guess most often, and a wrong guess hurts. Too short and the system can't be connected. Too long costs money and leaves a coil to hide.
A reorder also costs time: line sets ship from our Kentucky warehouse in 2 to 4 business days after the order is verified, then spend 3 to 7 days in transit. Measure once, carefully, for every room, and this page shows you how.
What line set lengths can you buy?
MRCOOL pre-charged line sets come in four lengths. Two longer lengths are made by joining two sets with a coupler kit.
| Length | How you get it | Price, from |
|---|---|---|
| 16 ft | One line set | $227 |
| 25 ft | One line set | $264 |
| 35 ft | One line set | $502 |
| 50 ft | One line set | $587 |
| 66 ft | 50 ft + 16 ft + coupler kit | about $1,239 for 6K to 18K units |
| 75 ft (max) | 50 ft + 25 ft + coupler kit | about $1,276 for 6K to 18K units |
Those are starting prices (prices as of November 2026) for the smallest pipe size. Bigger pipe costs more, for example a 16 ft set in 3/8 x 5/8 in is $271. Look at the jump from 25 ft to 35 ft: $238 more for 10 extra feet.
What length comes with the system?
- DIY Select and DIY EasyPro single zones include an 11.5 ft line set.
- Each DIY 5th Gen single zone complete system includes 25 ft.
- For 2- and 3-room DIY 5th Gen multi-zone systems, you choose the length for each room when you order.
- Our 4- to 6-room systems are listed with a 16 ft line set per room. Any room that needs more gets a longer line set chosen separately.
How do you measure a line set run?
Use a tape measure, or better, a length of string you can lay along the real route and measure afterward. Do it per room, and write each number down.
- Mark where the indoor unit will hang and where the 3 in hole goes through the wall behind it.
- Mark where the outdoor unit will sit, on a pad or on a wall bracket, and which side its connections face.
- Follow the route you'll really use: through the wall, down or along the siding, around corners, and through the attic or basement if the room has no outside wall near the unit.
- Measure each leg separately (up, across, down) and add them.
- Add a couple of feet at each end so the connections reach without strain and every bend stays gentle.
- Round up to the next available length.
A worked example
Say the indoor unit goes on an outside wall in a second floor bedroom, and the outdoor unit sits on a pad near the back corner of the house. The two units are about 15 ft apart in a straight line. The real path looks like this:
| Leg of the run | Feet |
|---|---|
| Through the wall, from the back of the indoor unit | 1 |
| Down the outside wall to just above the ground | 14 |
| Along the foundation to the pad | 6 |
| Over to the outdoor unit's connections | 2 |
| Slack at both ends | 3 |
| Total | 26 |
At 26 ft, a 25 ft set is too short, so the order becomes a 35 ft set. Before paying the extra $238, check whether the pad can move 2 ft closer to that wall. Moving the outdoor unit is often the cheapest fix in the whole project.
While you have the tape out, measure the part of the run that will be exposed on the outside wall. A LineGuard cover kit covers 12 ft for $129, so a 14 ft drop plus the run along the foundation needs two kits.
Can you cut a MRCOOL line set to length?
No. The refrigerant is sealed inside at the factory, and cutting the copper lets it out. At that point the DIY Quick Connect install is over and you need an HVAC tech with a vacuum pump and gauges.
Any extra length gets coiled in a loose loop near the outdoor unit. Follow the manual for your size on how to lay the coil, and keep every bend gentle so the pipe doesn't kink.
Next: which line set pipe size fits my indoor unit?
What if a room needs more than 50 ft?
Join two line sets with a coupler kit. A 50 ft set plus a 16 ft set makes 66 ft, and a 50 ft set plus a 25 ft set makes 75 ft. The kit is $425 for 6K to 18K units and $455 for 24K and 36K units, and it includes 75 ft of MC-5 cable, enough for the longest allowed run.
It shows how two pre-charged sets meet at the coupler, so you know what the joint looks like before you plan a 66 or 75 ft run.
Past 75 ft there is no option. If your measured path comes out longer, move the outdoor unit, pick a different wall for the indoor unit, or give that room its own single zone system with its own outdoor unit.
How do multi-zone limits change the plan?
On a DIY 5th Gen multi-zone, each room still has the 75 ft limit, and the MRCOOL manual adds three more rules:
- All line sets together can total 172 ft on the 3-room outdoor unit.
- On the 4- to 6-room outdoor units the total is 221 ft.
- Indoor units can sit up to 24 ft higher or lower than each other.
For a 2-room setup, check the multi-zone manual for your outdoor unit's total. Count the line sets you install at their full length, coil included, since refrigerant runs through the coil too.
Here is where location matters. Picture a 5-room house with the outdoor unit at one end:
| Room | Outdoor unit at the end of the house | Outdoor unit moved to the middle of the back wall |
|---|---|---|
| Living room | 50 ft | 35 ft |
| Kitchen | 35 ft | 25 ft |
| Primary bedroom | 50 ft | 35 ft |
| Bedroom 2 | 50 ft | 50 ft |
| Office | 50 ft | 35 ft |
| Total | 235 ft, over the 221 ft limit | 180 ft, within the limit |
Same house, same rooms. Moving the outdoor unit 20 ft along the back wall brought the plan back inside the manual's limit and cut the line set bill, since shorter sets cost less.
What if my setup is unusual?
What if the outdoor unit goes on a wall bracket?
A condenser wall bracket ($127 for 9K to 18K, $147 for 24K to 36K) lifts the outdoor unit off the ground. For an upstairs room, that can take several feet off the vertical drop. Measure to the bracket height, not to the ground.
What if the room has no outside wall?
Route through the attic or the basement. Measure the climb from the indoor unit to the attic floor, the run across the attic, and the drop down an outside wall to the outdoor unit. These routes often land in the 35 to 50 ft range, so measure before you assume 25 ft will do.
What if I'm buying DIY Select or DIY EasyPro?
Their 11.5 ft line set suits a room where the outdoor unit sits right on the other side of the wall, at about the same height. A longer run doesn't rule them out. MRCOOL's separate pre-charged line sets in the matching pipe size, plus a coupler kit past 50 ft, extend them the same way as the 5th Gen, and the line set chart in your system's manual names the exact part.
What changes is the cost. A 20 ft path on a Select or EasyPro means buying a 25 ft set, from $264, while the DIY 5th Gen single zone already has 25 ft in the box. Add that to the price gap when you compare lines.
What should you do next?
Walk the house with a tape and a notepad. For each room, write down the path in feet, the slack you added, and the next length up, then add up the total if it's a multi-zone.
When the list is done, order your pre-charged line sets along with the system. If a number looks close to a limit, call us at +1 (844) 999-9725, Monday to Friday, 9 AM to 5 PM EST, and we'll check the plan with you before you buy.
