Can Mini Split Lines Run Vertically Upward?

Suppose you want to install the condenser (outdoor unit) of your new mini split system above the air handler (indoor unit) or you need to run the mini split lines up (perhaps, to the ceiling space or attic) to reach the outdoor unit. In that case, you might be wondering if mini split lines can run in the upward direction. Here is the quick answer:

Mini split lines can run up vertically into the ceiling space, attic and even reaching the roof. The pressurized refrigerant can run against gravity subject to the maximum unit height difference specified by the manufacturer. For the drain line, a drain pump is needed to push the condensate water upward.

Where I’m from, it is very common to see mini split lines running upward, usually to the ceiling space, and then running horizontally and dropping to the outdoor unit. However, there are limits that you need to be aware of.

How Mini Splits Work?

Some people can’t get a grasp on how liquid such as refrigerant can flow against gravity. So, it is necessary for me to briefly explain how the refrigerant works in a mini split system.

As we all know, a mini split consists of an indoor and outdoor unit. The outdoor unit has a compressor. The compressor is the heart of the system. It pumps the refrigerant in a closed loop circuit.

The compressor of a mini split system pressurizes the refrigerant to a specific range of working pressure. This pressure is sufficient to drive the refrigerant around the circuit, regardless of whether the piping runs upward, downward or horizontally.

However, every mini split has a maximum piping length and a maximum unit height difference. As long as we stay within these two requirements, we can install the refrigerant line according to our situation.

Mini Split Piping Limits

Manufacturers will state the maximum piping limits for their mini splits in the brochure, submission sheet and installation manual. Although some mini splits are slightly difference from others, I summarized their typical piping limits to give you an idea:

Piping Limit9k & 12k BTU18k & 24k BTU
Maximum Length65 ft (20 m)100 ft (30 m)
Maximum Height40 ft (12 m)50 ft (15 m)

The maximum length measures one way from the indoor unit to the outdoor unit or reverse. This measures the entire piping length including all the bends, slopes, vertical drops and horizontal runs. The maximum length is not the physical distance between the indoor and outdoor units. Rather, it is about the refrigerant pipe length.

On the other hand, the maximum height is the physical vertical distance between the indoor and outdoor units. This is especially critical if you want to put the outdoor unit on the roof. In a multi-story building, you must check those indoor units located on the ground floor.

When the refrigerant piping length of a mini split system exceeds the limit, one problem is the lubrication oil is unable to fully return to the compressor. This causes the compressor to wear out and a replacement is needed.

I’ve had one project suffer from this problem previously. The compressor had to be replaced once every two months until the piping length issue was resolved. Compressors cost a lot to replace.

When you’re trying to stretch the piping to the limit, make sure none of the two limits are exceeded. What I mean is you may focus on meeting the maximum height requirement but forget to also check the maximum length. It happens.

Mini Split Drain Line

The drain line of a mini split system doesn’t have a specific limit like the refrigerant line. Mini split drain lines are designed to flow via gravity. The recommended gradient that allows good water flow is 1:100. Here is more about the basics of air conditioner condensate drain pipe installation.

When the mini split lines are intended to run upward, it means the drain line is also running upward. This makes the water flow against the gravity. Unlike the refrigerant, the drain line doesn’t have any pump to push it up.

So, you need to install an additional drain pump. See my post about mini split condensate pump for some reference photos.

However, the drain pump can only push the condensate water up to a certain height, usually to the ceiling space. Make sure you check the specifications before installing.

Conclusion

It is fine to run mini split lines upward. However, the refrigerant piping length and indoor-outdoor unit height difference must be within the manufacturer’s recommendation. As for the drain line, a drain pump is needed if you want it to flow against gravity.

Lastly, if you find running the mini split lines upward troublesome but don’t wish to run them exposed on the wall, consider running the mini split lines inside the wall (conceal them).

If you have anything to add (or ask) about this topic, leave a comment down below!

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