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HVAC and Plumbing Distributor
Picture of Steven Simmons

Steven Simmons

Technical Services Manager
Southwest District

Ductless Line Set Sizing

When installing Carrier/Bryant Ductless (mini splits) units please refer to the installation manual for the particular model of the unit you are installing or servicing. If you don’t have the needed manuals, they can be found on where you can also register for an account. You can also reach out to a Mingledorffs Technical Service Manager who would be glad to send them to you.

I will be referencing charts or tables from the manuals. In older literature, it is under “System Requirements”. In newer literature, it is under installation titled “Refrigerant Piping.” On multiport units it is under “Piping Requirements.”

Indoor and outdoor manuals should always refer to the same pipe diameters needed but, in the event that they differ, please refer to the install manual of the indoor unit when determining the lineset pipe sizing.

BEFORE installing a ductless unit, the information discussed in this article should be taken into consideration to ensure that the parameters are followed. If the wrong size lineset (according to the manual) is installed then then our recommendation would be to replace with the correct size.

Indoor Unit Pipe Sizes
Pulled from an indoor ceiling cassette 40MBCQ

The chart/table on outdoor units have loads more of information so I will assist in clarifying.

Refrigerant Piping
Pulled from an outdoor heatpump model 38MARB

*to keep things simple, we typically round close decimal numbers*

Min. Piping Length- This is the minimum allowed amount of lineset. Nothing less than 10 Feet.

Standard Piping Length- this is how much lineset the unit is precharged to handle. Do not remove charge to compensate for linesets that are shorter than 25 feet.

Max. outdoor-indoor height difference- how far you can separate the indoor from the outdoor vertically, two labels are show- IU indoor unit above OU outdoor unit and vice versa.

Total Maximum Piping- this is the maximum allowed pipe length. Installations beyond this lineset length will not be approved nor recommended.

Additional refrigerant charge- if your lineset is over 25 feet but not longer than the MAX, this is how many ounces per foot should be added to the unit for proper operation.

Suction Pipe- the suction hookup size at the outdoor unit.

Charge amount- how much charge the unit has from factory to cover 25ft of lineset.

Piping and Refrigerant
Pulled from Multiport outdoor unit 38MGR

These units are more complex and have more variables to consider.

*to keep things simple, we typically round close decimal numbers*

Min. Piping Length per each indoor unit- This is the minimum allowed amount of lineset for each indoor unit

Standard Piping Length per each indoor unit- this is the amount of lineset that has been “reserved” for each indoor unit for refrigerant charge purposes.

Max. outdoor-indoor height difference- how far you can separate the indoor from the outdoor vertically. Two labels are shown- IU indoor unit above OU outdoor unit and vice versa.

Max. height different between indoor units- if the indoor units are on different levels, then they should not exceed this amount of vertical separation amongst themselves.

Max. Length per each indoor unit- no indoor unit should have a lineset longer than this number. Do not exceed this number for any indoor unit lineset.

Max. Piping Length with no additional refrigerant charge- add together all of the lineset lengths for all the indoor units. If your lengths are above this number, then additional charge is needed.

Total Maximum Piping Length per system– when adding together all the indoor pipe lengths, this is the total length that the unit can support. Pipe lengths greater than this are not approved nor recommended.

Additional refrigerant charge- if your total lineset length is over the “Max. Piping Length with no additional refrigerant charge” amount, this is how many ounces per foot should be added to the unit for proper operation.

Pipe sizes: these show the pipe sizes with an asterisk (*) and then the quantity of those ports.
For example: from the 36K– 1/2 *2+3/8*2
This means 2 at ½ and 2 at 3/8.

In the event that the correct line set size is ran and it is not the same size as the hookup of this unit, use the factory supplied adapters to make the connections.

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Commercial Parts

[email protected]
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