How Far Can You Run An AC Line Set?

Dennis Howard
by Dennis Howard

Installing a refrigerated AC system always comes with some challenges. One of the greatest is finding the optimum place to set the condensing unit. Many small residential lots limit the places that a condensing unit may reside. Many times, these locations may be far from the HVAC unit and the condensing coil. The question of how far you can run an AC line set is critical to a proper installation.

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In general, seventy-five feet is considered the maximum distance a line set can be run. However, there is no absolute rule about the length of an AC line set. The variables that affect the maximum line set length are numerous. The recommendations and requirements of the manufacturer must also be considered. Local building codes can also figure into the equation.

In any case, the first reference to consider is the manufacturer’s specifications. Other factors may affect your decision, such as the type of HVAC system and condenser, the elevation changes in the system, and requirements for additional equipment required for proper operation of the HVAC system.

How to Determine the Maximum AC Line Set Length

When you start to locate the condensing unit for your new HVAC system, it is important to consider the AC line set length. Several factors must be considered to ensure the proper operation of your HVAC system. Some factors are more subtle than many people realize.

Even the smallest detail can be the difference between an efficient and effective installation. Failing to attend to the details is a mistake many do-it-yourselfers make with their HVAC project. There are no shortcuts to performing a proper AC line set in your home.

How Do I Measure to Ensure My AC Line Set Length is Correct?

Some homeowners make a critical mistake when selecting the site for their refrigerant condenser is the actual length of the AC line run. The term used by HVAC professionals is “total equivalent length.”

The length of your AC line set is not a linear measurement from the HVAC unit to the condensing unit. No AC line set runs directly to the HVAC unit. The AC line set must negotiate through the house, often following walls or attic spaces to reach its destination.

This necessitates numerous bends, ups, and downs. Rather than measure the direct linear distance, you must calculate the “total Equivalent length” of the line set run. This measurement considers the total length of the AC line set needed to negotiate the route from the condensing unit to the HVAC unit.

How Long Can My AC Line Set Be?

The best and most accurate information about the AC line set length for your HVAC system is the Manufacturers specifications and recommendations. All HVAC manufacturers provide this information with the user and installation manuals that come with the HVAC systems.

The information in the installation guide should be the rule and guide for your installation. If you deviate from the manufacturer’s recommendations and specifications, you risk voiding the warranty. An improper AC line set may damage the condenser and require extensive repairs or replacement.

What is the Problem with Long AC Line Sets?

The major problem with long AC line sets is friction loss in the lines. As the liquid refrigerant moves through the refrigerant line, it encounters friction from the tubing walls. The longer the refrigerant line, the more friction loss affects how much refrigerant gets to the evaporator coil.

The friction loss effects may be offset by using larger diameter refrigerant lines. However, some compressors may not be able to deliver enough flow rate through the larger diameter lines. The overall operation and efficiency of the HVAC system will suffer if the installation is not precisely calculated.

What Things Should I Consider When Installing an AC Line Set?

Beyond the AC line length set, there are other factors to consider. Among these are

  • The size of the refrigerant lines
  • The location of the condenser and evaporator coil
  • The requirements set forth by the manufacturer.

These factors may require additional equipment to be included in the installation to ensure the proper operation of the condenser and its working life. System efficiency can also suffer if the AC line set is not properly planned and installed.

Does the Length of My AC Line Set Affect the Size of the Line Set?

Determining the proper size of refrigerant lines for a given length of AC line set is a complicated issue. If the line size, size of the condensing unit, and the length of the run are not carefully calculated, the system may not operate at peak efficiency. Poorly made decisions about the AC line set size can damage the condensing unit.

Most HVAC manufacturers offer considerable information about sizing refrigerant lines based on the size of the condensing unit and the length of the AC line set. The manufacturer has the best information in all cases, and their recommendations should be followed closely.

Finding the Correct AC Line Set Size

In general, the following chart can help you determine the most efficient size of refrigerant line for your condensing unit and the length of the line set. Remember that these are general recommendations. Always follow the specifications in the manufacturer’s installation guide for your system.

Condenser Unit Size0 – 25 ft Length of Run25 – 50 ft Length of Run51 – 75 ft Length of Run75 – 150 Ft Length of Run
33/43/87/83/81 1/83/81 1/83/8
3.57/83/81 1/83/81 1/83/81 1/83/8
47/83/81 1/83/81 1/83/81 1/83/8
57/83/81 1/83/81 1/83/81 1/83/8

What if I Need to Run an AC Line Set Longer Than 80 Feet?

Most manufacturers recommend additional equipment installed with the system if the total equivalent length is longer than 80 feet. The usual recommendations include the following additional system enhancements.

  • Crankcase Heater – In longer AC line set runs, the lubricating oil in the refrigerant lines may migrate within the system. This migration can starve the compressor of needed lubrication under some circumstances. Adding a crankcase heater in the system minimizes the risk of oil migration within the system.
  • Thermostatic Expansion Valve (TXV) – A TXV valve separates the high pressure and low-pressure sides of an air-conditioning system. The TXV valve is necessary for some systems, particularly those with long line set runs, to ensure system efficiency. Excessive liquid refrigerant is prevented from returning to the compressor by regulating the refrigerant flow. This can result in a condition known as floodback.
  • Hard Start Capacitor – Often, long line sets require an increased refrigerant charge level to operate efficiently. This can cause the compressor in the condensing unit to overwork when it starts. A hard start capacitor assists the compressor when starting to extend compressor life.
  • Liquid Line Solenoid – Provided you don’t have a heat pump, some line set runs over 80 feet may require a liquid line solenoid. This device can help minimize the risk of oil migration and consequential damage to the compressor.

Your HVAC technician and the manufacturer’s recommendations and specification should be the rule and guide to long AC line set runs.

What if My Condenser is Above my Evaporator Coil?

Some situations may require the condensing unit to be mounted above the evaporator coil on your HVAC system. The length of the line set must always be considered. In installations where the Condensing unit is above the evaporator coil, most manufacturers suggest the installation of an oil trap.

If the height difference is 15 to 25 feet, one oil trap is usually adequate to protect the system. Where the height difference is 25 – 50 feet, most manufacturers recommend installing two oil traps. If the height difference exceeds 50-feet, three oil traps should be installed in the system.

Does the Vertical Height of the AC Line Set Affect Efficiency?

The question is not the height of the AC line set but the position of the Condensing Unit in relation to the evaporator coil. If the compressor is below the evaporator coil, you can see less efficiency from your HVAC system.

In a horizontal AC line set run, the overriding issue is friction loss in the lines. The longer the AC line is set, the greater the flow rate is reduced in the line. For example, a compressor on the same level as the evaporator may deliver 100 units of flow. The evaporator will only see 90 units of flow because of friction loss.

When the compressor is below the evaporator unit, the flow rate can be reduced enough to lower the unit’s efficiency. In addition, the flow rate in the refrigerant lines may not be sufficient to carry the lubricating oil through the system.

The Shorter, the Better – A Rule of Thumb for AC Line Set Length

The practical truth to the problem of AC line set length is to keep the refrigerant line runs as short as possible. Sometimes, locating your condensing unit based on your situation may necessitate a longer AC line set. If a longer run is required, make sure you are within the manufacturer’s recommendations. Installing additional equipment to ensure the proper operation of your HVAC system is also recommended.

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Dennis Howard
Dennis Howard

Dennis is a retired firefighter with an extensive background in construction, home improvement, and remodeling. He worked in the trades part-time while serving as an active firefighter. On his retirement, he started a remodeling and home repair business, which he ran for several years.

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