When installing the MRCOOL DIY 5th Gen 36,000 BTU 3-Zone Mini Split System, one of the most overlooked—but critically important—components is the line set. These insulated copper tubes carry refrigerant between your outdoor condenser and each indoor air handler. If you’re a DIYer like Samantha, understanding line set sizing and extensions will help you plan the perfect layout without hitting installation roadblocks.
Let’s break down what you need to know about line sets for a multi-zone mini split.
🧰 What Comes Standard with the MRCOOL 3-Zone System?
MRCOOL includes the following pre-charged Quick Connect line sets in most DIY kits:
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16-foot line set per 9k indoor unit
That gives you a total of 3 x 16-foot connections between the air handlers and the condenser. These line sets are fully sealed, pre-flared, and charged with refrigerant, so no vacuum pump or special tools are needed.
📏 How to Measure Line Set Length Needs
To ensure you order the correct lengths:
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Measure the straight-line distance from each indoor unit to the outdoor condenser
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Add extra length for:
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Bends and wall penetrations
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Routing around windows, doors, or decks
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Vertical drops from attics or upper floors
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Tip: Always round up. It's better to have a little extra slack than come up short.
📐 Recommended Minimum & Maximum Lengths
| Specification | Value |
|---|---|
| Minimum per zone | 10 feet |
| Maximum per zone | 75 feet (with extensions) |
| Total system max length | ~150 feet combined (varies) |
| Elevation difference | Up to 49 feet (max vertical) |
Note: Longer line runs can reduce efficiency slightly, so balance convenience with performance.
🔧 What If 16 Feet Isn’t Enough?
If your layout requires more than the included 16 feet, you’ll need a MRCOOL Line Set Extension Kit. These come in:
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16-foot, 25-foot, or 50-foot extension options
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Each kit includes:
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Pre-charged extension line
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Quick Connect coupler
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Insulated sleeve
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These kits allow you to extend the original 16-foot lines without losing refrigerant or voiding your warranty.
🧩 Coupler Tips & Routing Strategies
When joining two line sets:
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Use the included coupler kit (threaded quick connectors)
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Support the joint with brackets or a strap to reduce vibration
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Wrap joints in UV- and weather-resistant insulation foam
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Mount couplers off the ground if possible to avoid damage or corrosion
Routing ideas:
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Use rain gutters to hide vertical lines
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Run along baseboards in basements or garages
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Use wall sleeves for clean siding penetrations
📦 Samantha’s Setup Example
Samantha’s MRCOOL 3-zone layout:
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Bedroom (2nd floor): Needs 25 feet → uses a 16' + 9' loop
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Home office (1st floor): Uses stock 16-foot line
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Guest room (opposite end): Needs 30 feet → uses 16' + 16' extension kit
She mounts the condenser on the rear patio and uses gutter downspouts to conceal vertical runs.
⚠️ Common Mistakes to Avoid
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Over-bending the copper line (can kink and reduce flow)
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Cutting pre-charged lines (will void warranty and release refrigerant)
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Not sealing wall penetrations (invites pests and water damage)
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Exceeding total run lengths without checking spec sheets
🧠 Pro Tip: Use MRCOOL’s Line Set Calculator Tool
Some retailers offer line set planning tools to help you map your layout and recommend lengths and extensions. Check the MRCOOL site or trusted distributors.
✅ Final Thoughts: Plan Before You Drill
With a little planning, Samantha (and you) can confidently install all three zones without drama. The MRCOOL DIY line set kits are some of the most homeowner-friendly options available.
Just remember:
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Measure each run and round up
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Use the proper extension kits and couplers
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Support and insulate all line connections
In the next topic we will read about: Maintaining Your MRCOOL System: Filter Cleaning, App Updates & More
