Efficient Heat Pump Operation: Exploring The Line Set

Photo of author

By Debarghya Roy


Heat pumps are an efficient and cost-effective form of home cooling and heating. To ensure that heat pumps operate properly, a line set must be installed correctly. Heat pump line sets connect the outdoor air conditioner or heat pump to the indoor air handler, transferring refrigerant between each in order to regulate temperatures. Due to their importance for maintaining optimal performance, it is essential that homeowners choose the right line set for their system.

Heat Pump Line Set

Image of heat pump line set in a heat pump

Key Takeaways

  • Heat pump line sets are an integral component of HVAC systems, connecting the outdoor air conditioner or heat pump with the indoor air handler.
  • The size and material of a line set should be considered when selecting one for maximum efficiency. Copper lines are preferred due to their strength and resistance to corrosion over time.
  • Different types of lines can be used, including standard copper lines, custom lines, minisplit lines, or pre-insulated line sets.
  • Proper installation is important for optimal performance along with regular maintenance throughout its life cycle in order to reduce energy costs associated while ensuring safety standards remain followed at all times!

Definition Of Heat Pump Line Sets

A heat pump line set is an assembly of copper tubing and wiring used to connect the outdoor air conditioner or heat pump with the indoor air handler. The two semi-flexible copper pipes, one larger and one smaller, typically make up the line set kit. This assembly allows for effective flow of both refrigerant and electrical current between the units. Many models also feature factory flared ends that make installation simpler when using a compatible fitting such as Airex from Air-Zenith Incorporated.

Components Of Heat Pump Line Sets

Refrigerant Line Sets

Refrigerant line sets are typically made from copper and consist of two tubes, one to carry refrigerant to the indoor unit, and one to return it back outside. 

The ends of each tube must be securely connected with flare fittings that are soldered onto the tubing, which helps maintain a tight seal.

Pipe Insulation Sleeve

An insulation sleeve is installed around the refrigerant lines to reduce frost and condensation buildup and protect from outdoor temperatures.

Electrical Wiring

Electrical wiring is used to connect the indoor and outdoor components of the system. For example, most systems will need an electrical power supply line connecting the indoor breaker panel.

Condensate Drain Line

A condensate drain line is necessary for efficient operation and can consist of either flexible or rigid PVC piping which runs from the evaporator coil located within the air handler unit outside. 

This polymer piping helps channel away excess moisture that may come off during the normal operation of an air conditioning unit.

Types Of Heat Pump Line Sets

Standard Copper Line Sets

Standard copper line sets are the most common type of heat pump line sets, and they are preferred because of their durability. Copper is a good material for such pipes due to its strength and characteristics which make it resistant to corrosion over long periods of time.

Standard copper line sets usually come in two sizes, 3/8” or 7/8” diameter depending upon the specific requirements. It is important to select the right diameter as this will affect performance, energy efficiency and cost savings that you can expect from your Heat Pump system.

The length of standard copper lines typically ranges from 25 feet up to 100 feet depending on the physical parameters (elevation difference) between your outdoor compressor unit and the interior evaporator coil.

The fan coils should also be taken into consideration when deciding on a suitable line set size since each will have different capacities specified by the manufacturer. Both lengths are available with factory flared ends so you don’t have to worry about cutting distant cuts prepping tubing already installed position indoors or outdoor units.

Custom Line Sets

Custom line sets are a great way to customize an HVAC installation. This type of line set allows for more precise fit, spacing requirements and overall performance in unique applications such as commercial installations or tight spaces.

With custom line sets, professionals are able to create customized sizes that may not work with standard copper lines. Custom linesets can come with factory-flared ends and ready-to-connect fittings so there is no need for thorough measuring or additional preparation before installation.

Creating a custom heat pump line set requires some precision and technical know-how but it’s becoming increasingly easier to do thanks to newer technologies like PVC bends using a heat gun instead of cutting each individual pipe length separately by hand.

Heating elements such as those found in dryer vent hose kit systems offer greater flexibility in pipeline design when putting together complicated configurations because cuts don’t have to be as specific and repairs can often be easily patched up without entirely replacing the entire system if one element gets damaged during piping installation.

Mini-Split Line Sets

Mini-split line sets are a critical component of a mini-split system that connects an outdoor unit to the indoor evaporator. These lines are made from either copper or aluminum and have factory-flared ends for easy connection and airtight sealing within the wall.

The size of the mini-split line set is very important, as too small or large of a line set can cause malfunctions in your mini-split system due to incorrect refrigerant pressures.

While copper line sets are most commonly used, aluminum is cheaper but requires more maintenance to prevent corrosion and leaks over time. Airex brand also offers pre-insulated foam line sets with premade connections for easier installation but these tend to be more expensive than traditional options.

Pre-Insulated Line Sets

A pre-insulated line set is a type of heat pump line set that offers significant advantages when it comes to energy efficiency, installation time, cost savings and durability.

Pre-insulated line sets are made with highly durable, pre-flared and insulated liquid and suction lines in order to reduce the amount of work needed for installation. This eliminates the need for additional insulation which can be costly if done professionally or result in poor performance if not done properly.

They also eliminate possible points where corrosion could form such as pinholes forming on copper ductless line sets over time. Insulated AC line sets offer improved dependability compared to standard copper models by providing protection from extreme temperatures during transport and installation.

Lengths up to 250 feet along with different sizes ranging from 1/4 inch (6 mm) up 16 inches (410 mm) are available for precharged line sets enabling. 

Benefits Of Using A Heat Pump Line Set

Heat pump line sets provide a highly efficient and cost-effective way to heat or cool your home. Installing them correctly can result in greatly improved energy savings, enhanced comfort levels, lower utility bills, and better overall performance of the system.

Energy Efficiency

Heat pump line sets significantly contribute to the energy efficiency of a home. The length, size, and type of pipe used can all affect how much energy is consumed by the heat pump system.

Standard copper lines are often sufficient in most cases, but custom options such as pre-insulated mini-splits allow for even greater control over the amount of energy necessary to run a heat pump system.

Additionally, proper installation is essential in order to maximize performance and ensure maximum efficiency from the entire system. 

Moving air within lengths more than 100ft requires additional ducts or larger diameter piping for optimal efficiency. An improper installation may reduce efficiency by up to 20%.

Cost Savings

Heat pump line sets are an essential component of a heat pump system, enabling the efficient transference of heated or cooled air throughout your home. Due to their efficiency and effectiveness at regulating temperature, heat pumps significantly reduce energy use and utility bills.

When choosing a heat pump line set you should take into consideration factors such as size, length and material used in order to ensure maximum performance and efficacy from your system.

Heat pumps come in different SEER (Seasonal Energy Efficiency Ratio) ratings which will greatly influence how much energy is saved. Higher-end units with 19+ SEER rating can cost up to four times more than standard models but tend offer greater savings in terms of energy costs.


Achieving comfort is an important factor to consider when choosing the best heating system for your home. Heat pumps offer improved comfort and steady indoor humidity levels throughout the year compared to other traditional forms of heating.

Heat pumps absorb and move ambient heat rather than burning fuel, making them more energy-efficient with lower CO2 emissions

The use of heat pumps can help you maintain a comfortable temperature in your home since they have a ‘comfort zone’ that operates at around mid-60°F but are also designed to function better as temperatures approach the required comfort level.

Factors To Consider When Choosing A Heat Pump Line Set

When looking for the right heat pump line set, it is important to consider various factors such as size, length, materials used and temperature considerations.


Knowing the correct size for a heat pump line set is critical when installing one. The size of the house or building is an important factor in determining heat pump capacity, as larger houses need greater heating and cooling power.

Homeowners need to be aware that their climate can also affect the ultimate choice in terms of both type and capacity of system required for optimal comfort levels.

A 12000 BTU system typically uses a 5/8” line (OD) per foot with at least 15ft long lineset and a 24000 BTU system usually requires two 15 ft 3/4″ lines (OD). 

18000-36000 BTU systems would use either two 25ft 7/8″ lines or three 25′ 5/8” x 7/8″ tubes OD depending on other environmental factors such as temperature differences etc. To ensure proper sizing, calculate by subtracting (-25 Celsius outside minus +7 warm inside gives you 32 which means 3 ton if the difference <13 then suggest 2 ton).


When it comes to selecting a heat pump line set, length is of utmost importance. Choosing the right size and length of a line set will ensure that the home has sufficient heating or cooling according to its size and that energy efficiency is thus maximized.

The recommended minimum required for many residential systems is 25 feet but this number can vary greatly depending on conditions such as the size of liquid line used in the system, location of installation (i.e., basement or an attic) or if additional connections from equipment are necessary at mid-level of extension runs.

In most cases, the maximum length for line sets ranges between 50 ft to 75 ft. However, some manufacturers may offer shorter lengths up to 30ft. 

Materials Used

Heat pump line sets are available in a number of different materials, such as copper, aluminum, and other metals. Copper is the most popular choice because it provides excellent heat transfer capability.

Aluminum on the other hand is a cheaper option but its insulation properties can be less effective when compared to that of copper. 

Plastic or pre-insulated options also exist and offer additional protection against corrosion and weather conditions for outdoor installations while reducing installation time due to their lighter weight.

Each material has its own advantages and disadvantages so it’s important to select the right one based on individual needs, environment factors like temperature swings or potential frost damage for outdoor applications, as well as budgetary requirements.

Temperature Considerations

When choosing and installing a heat pump line set, the temperature is an important factor to take into account. Heat pumps operate at their most efficient when temperatures are mild.

Extremely cold temperatures can cause the system’s indoor coils to freeze up, impairing its efficiency and potentially damaging components of the system. It is therefore important to select materials for your heat pump line set that will not be damaged in extreme temperature fluctuations.

For instance copper lines are more durable than plastic linesets which may warp and degrade as temperatures drop below freezing. 

Additionally, it is wise to insulate both outdoor and indoor lines using insulation sleeves or cladding so that losses due to sweat or dryness due to surface evaporation do not significantly impact performance levels.

Different Covering Options For Heat Pump Line Sets

Covering a heat pump line set is essential to protect it from the elements and ensure its optimal performance.

Heat Pump Line Set Covers

Heat pump line set covers are essential in protecting and hiding the lines and drains of a heat pump system. Line set covers come in various sizes, materials, and functional options so that homeowners can find one that best fits their home’s aesthetic or function.

Line sets are often made with Airex Flexguard which is installed at length along the pipe before the standard dibond.

Tape For Heat Pump Line Sets

Tape is an effective way to protect heat pump line sets from unwanted moisture, dirt, and other airborne debris. There are several types of tape suitable for this purpose, such as duct tape and self-amalgamating silicone rubber tapes.

Self-adhesive non-asbestos fibrous jointing tapes are also a viable option. These are robust, temperature-resistant alternatives to traditional cement/asbestos mastic filler tapes.

These latter two kinds of tapes specifically form water barriers on the outer surface of the copper line set tubing that can last up to three decades without needing maintenance or replacement.

When it comes to protecting your HVAC system’s sensitive connections, using these tapes instead of line set covers or insulation may be a better solution due to their superior waterproofing ability and longevity.

Insulation For Heat Pump Line Sets

When it comes to heat pump line sets, insulation is an important factor for ensuring the longevity and efficiency of the system. Without proper insulation, condensation can occur on the lines or evaporator coils which decreases performance.

Heat pump line set insulation options include tape-wrapping steel straps around copper pipes or using pre-insulated flex ducts (also known as a mfr part), wrapped with fiberglass with an R8 value that fits into factory flared ends on both sides of each pipe section. 

These are convenient because they require no additional work before installation.

Additionally, liquid tight neoprene covers may be used for protecting wire cables from moisture while providing thermal protection in harsh environments. Ultimately, choosing the right type of insulation for a particular application will depend on its size and length requirements since certain materials offer better insulation properties than others at lower thicknesses per inch.

Importance Of Proper Installation

When it comes to heat pump line sets, proper installation is of the utmost importance. Incorrectly installed lines can lead to improper system performance and reduced efficiency, as well as potential safety risks for both users and the building itself.

Without a correctly sized and properly sealed line set, liquid refrigerant can become exposed to areas containing air or moisture which could cause a fire in extreme cases.

Refrigerant lines must also be properly sized based on the type of equipment being used along with any other obstacles that might affect its performance such as insulation or longer runs over 30ft .

An undersized line will decrease capacity while an oversized one will lead to increased sound levels due to insufficient pressure drop through the line at peak loads. Not only this but improperly selected fittings on connections between conduit or tubing could create additional points of failure within the system.

Installation Of Heat Pump Line Sets

It is important to have a professional installer properly install the heat pump line set in order to ensure safe and efficient operation.

Proper Installation Steps

It is essential to properly install a heat pump line set to ensure the safe and effective operation of the heat pump system. 

Improper installation may lead to safety hazards such as refrigerant leaks, which can be dangerous for humans and animals. By following the steps below, you can avoid these risks while ensuring that your heat pump system is installed correctly.

  1. Carefully map out where all components need to be placed prior to beginning installation. This includes both indoor and outdoor units, line sets, wall mount brackets, venting ducts (if applicable), etc. This ensures that everything fits together perfectly during installation, reducing potential complications later on down the road.
  2. Make sure all items are compliant with local building codes before proceeding with any construction or assembling activity; some municipalities require special permits for HVAC work depending on size/type/location of equipment being installed.
  3. Remove existing refrigerant lines from previous heating/cooling systems. If they are present in order for them not to interfere with newly-installed lineset material. An example would be an old R22 air conditioning unit having its copper piping removed so new pipe won’t get mixed up alongside it when reattaching connections between indoor & outdoor sections of split-type models like “mini-splits” or other configurations designed by manufacturer instructions accordingly. 
  4. Use properly sized cable ties & waterproof conduit routing materials rated specifically by NFPA 79 requirements outlined. This could also prevent bad safety conditions like one incident learned recently about improper tie-downs made by electricians who didn’t know better unknowingly caused deaths after being found responsible through forensic investigations done right away before reviews even took place.
  5. Before attaching main power sources locate GFCI equipped outlets necessary for connection compliance because high amp draw electronics demand higher than usual current levels otherwise risking malfunction loss leading

Importance Of Professional Installation

  • Professional installers have the necessary knowledge and expertise to correctly install heat pump systems, ensuring optimal performance and efficiency.
  • Certified professionals can customize the installation according to your specific needs, including sizing the system and selecting the right components, resulting in better overall performance.
  • Professional installers are familiar with local building codes and regulations, ensuring that the installation meets all safety and legal requirements.
  • Improper installation can lead to various issues such as poor cooling, inadequate airflow, and reduced energy efficiency. Professional installers can prevent these problems through proper installation techniques.
  • Professionally installed heat pump systems are more likely to operate efficiently, leading to lower energy bills and long-term cost savings.
  • Many manufacturers require professional installation for warranty coverage. By hiring a professional installer, you can ensure that your system remains eligible for warranty support.
  • HVAC systems involve electrical connections, refrigerant handling, and other potentially hazardous components. Professional installers are trained to handle these aspects safely, minimizing the risk of accidents or injuries.
  • Hiring professionals provides peace of mind, knowing that your heat pump system has been installed correctly and will operate reliably for years to come.

Common Issues And How To Fix Them

Common IssuesHow to Fix Them
Improper sizing of line setsObtain a professional assessment for selecting the correct pipe size based on the specific application requirements.
Inefficient heating system or no heatEnsure proper sizing and installation of line sets, and consult with a professional to diagnose and address the issue.
Frozen indoor coilsVerify that temperature ratings are observed during installation and consider implementing measures to prevent freezing.
Inadequate compressor performanceFollow correct temperature ratings during installation and seek professional assistance to optimize compressor operation.
Extreme pressure fluctuationsProperly size the line sets and consult an expert to address pressure-related issues affecting the heat pump system.
Efficiency loss due to freezing tempsCalculate and protect copper lines running outside with insulation or protective covers to maintain optimal efficiency.
Burst pipesEnsure proper insulation and protective measures are in place to prevent freezing and potential damage to the line sets.

Maintenance And Inspection Of Heat Pump Line Sets

Regularly inspecting and maintaining heat pump line sets is essential to ensure their performance and longevity.

Importance Of Regular Maintenance

Regular maintenance of a heat pump system is key to its efficient operation and longevity. Neglecting routine maintenance can lead to breakdowns, reduce the system’s lifespan, and increase energy bills.

Preventive maintenance on a heat pump should include checking specific components such as the charge for 15-foot line sets. 

Furthermore, making sure all connections are sealed tightly with insulation tape or applying liquid sealant helps prevent undesired air leakage from the outside environment into the home.

Tips For Maintaining And Inspecting Heat Pump Line Sets

A heat pump line set runs between an indoor and outdoor unit, transporting refrigerant to and from the compressor as part of a heat pump system. 

These sets consist of two copper pipes with flared ends, wrapped in foam insulation and covering sealing tape. 

In order to ensure trouble-free performance, it’s essential to maintain and inspect these components regularly. Here are some tips for maintaining and inspecting heat pump line sets:

  1. Inspect ducts, filters, blower, and indoor coil for dirt and obstructions that could hinder performance or create airflow issues.
  2. Diagnose and seal duct leakage with mastic or silicone caulk hammering out any snags that would affect airflow.
  3. Verify adequate airflow by measuring temperatures and pressing against registers with your hand to make sure they are working properly.
  4. Pressure test the line set for leaks using pressurized nitrogen, soapy water solution, or hydraulic oil after installing it properly using chamois or a large sponge to clean off the refrigerant lines before the inspection begins.
  5. Have a trained service technician inspect the heat pumps at least once a year to ensure trouble. Depending on the age of the system you may need more frequent inspections of the line sets as well as other critical components such as contactors, capacitors, fans/blowers, etc..
  6. Keep surrounding air temperature lower than recommended. Tthis will reduce stress on your equipment caused by warmer outside conditions (ideally 5-8°F lower).


What is a heat pump line set?

A heat pump line set consists of two copper tubes used to connect an outdoor air conditioner or heat pump unit to the indoor evaporator coil. The smaller tube is known as the liquid line and carries refrigerant from the indoor coil to the outdoor condenser; while the large tube is called a suction line that brings compressed gas back inside from outside.

How long should my heat pump line set be?

The length of your Heat Pump Line Set depends on several different factors including distance between outdoor & indoor units, size & temperature of available space and specific requirements outlined by the manufacturer’s specifications when replacing/installing new system components (i.e., compressor sizing needs). Generally speaking, selecting the right-sized tubing can reduce strain placed upon the system over time therefore delivering consistent performance levels while better meeting energy efficiency goals outlined prior to purchase/installation date(s).

What kind of insulation do I need for my Heat Pump Line Set?

When installing a Heat Pump Line Set it is important to properly insulate both lines with pull-through foam or polyethylene sleeve in order to ensure optimal performance settings during colder temperatures encountered especially outdoors where extreme weather conditions could be present throughout year(s) ahead leading up to eventual repair/maintenance service calls if not addressed initially at start-up phase installation process ramps up completion rates desired over any period runtime specified or expected going forward end user site visits scheduled post product release dates announced more widely public (& private requests honored accordingly timeline alloted multiple projects simultaneously staffed).

Is there anything else I should know about installing a Heat Pump Line Set?

In addition to using sufficient insulation along the length conducted supporting Tube Services necessary secure quality standards respected detailed reports generated approved industry experts consulted commissioning data acquired early process begins throughout entire project deploy management solutions implemented operating systems monitored predict issues could arise due complications discovered maintenance sessions often recommended avoid costly service charges become increasingly popular direct result increased usage recently reported outlining increase areas practice methodologies applied preventative treatments praised inspection crews assigned provided additional insight requires updating crucial information records updated procedures routinely safeguarded reinforce longevity operation continue to preserve equipment resource costs.

What size line set should I use for my heat pump?

The size of the line set is an important consideration for the proper performance of the heat pump system. It is essential to consult the manufacturer’s recommendations and follow these guidelines to ensure optimal efficiency and prevent any potential issues or damage.

What materials should be used for heat pump line sets?

Line sets typically consist of two semi-flexible copper pipes that connect the outdoor air conditioner or heat pump to the indoor air handler. Copper is the preferred material for line sets due to its durability, conductivity, and resistance to corrosion.

What are the consequences of improper installation or maintenance of heat pump line sets?

Improper installation or maintenance of heat pump line sets can lead to reduced system efficiency, increased energy consumption, and higher costs. Additionally, it can cause potential safety hazards such as refrigerant leaks or electrical issues. It is essential to work with a qualified professional for installation, maintenance, and any necessary repairs to your heat pump system and its line set.


The use of a properly sized and installed heat pump line set is important for both safety, efficiency, and reliable performance. The right line set can have substantial energy savings which translates to cost savings over time. Different types of line sets are available, including standard cooper lines, custom lines, mini-split lines, and pre-insulated lines. It is also necessary to choose the right covering option such as using insulation or other protective materials around the exposed parts of the line set. Proper installation with professional help ensures that your system performs optimally while regular inspection and maintenance will ensure you get many years of safe usage out of your heat pump system.

Heat Pump