Inspecting Insulation on Air Conditioner Refrigerant Lines

Knoji reviews products and up-and-coming brands we think you'll love. In certain cases, we may receive a commission from brands mentioned in our guides. Learn more.
The insulation on the suction or vapor lines connected between your furnace and outdoor condensing unit is very important in maintaining system efficiency, reducing energy consumption, and extending the life of your air conditioning system. You should ins

A common defect found during home inspections is either missing or deteriorated insulation on the air conditioner refrigerant lines, in particular the suction line. 

On a split system air conditioner or heat pump the refrigerant line-set runs between the evaporator coil inside the air handler or furnace inside the home and the condensing unit that contains the compressor and condenser coil on the exterior of the house. The refrigerant moves between these two units by way of two lengths of copper tubing; the liquid and vapor lines.

Liquid Line – The smaller diameter copper tube that carries liquid refrigerant between the two units. This line gets very hot when operating as the refrigerant is pressurized.  In most cases this line should not be insulated. There are circumstances where the line should be insulated when the surrounding temperatures are high to reduce heat gain, as in the case of attic installations. Another situation where the liquid line can be insulated is when the suction and liquid lines are clamped together so as to prevent heat transfer from the liquid to the suction line.

Vapor or Suction Line – The larger diameter tube is the suction line that carries refrigerant vapor between the two units, this line is very cold, around 20°F when the unit is in operation as the vaporized refrigerant cools as it expands.  This line should be insulated for the entire length to prevent the vapor from gaining heat from the home or the outdoor temperature.  If this line is exposed to ambient conditions, the efficiency of the air conditioning system will be reduced.


Condensation on the exterior section of the suction line is usually harmless if unit sits on the ground, but as stated previously, system will reduced efficiency and will have to run longer to maintain the room temperature setting on the thermostat. Missing or damaged insulation can also cause premature compressor failure due to the extended run times.

Refrigerant lines insulation should be also installed from the air handler or furnace penetration to the condenser unit and even inside the condenser to the point where the line enters the compressor. Verify that the suction line is insulated inside your air handler unit as well since uninsulated lines will sweat and the condensation may damage internal components such as the heat exchanger.

Missing damaged or improperly installed insulation on the refrigerant line may cause corrosion, discoloration, could compromise internal components of the air conditioning and heating system, and significantly shorten its life span of damage the unit which will result in costly repairs. Missing or inadequate insulation can cause ice to form on the suction lines, especially near the compressor or evaporator coil, and reduce system efficiency.

Ice forming where foam insulation is damaged or missing

Missing insulation on the suction line running inside walls, ceiling cavities, or through the attic will also result in condensation which could result in damage to interior finishes and can cause mold growth.

Missing refrigerant line insulation in an attic space

If the insulation on your air conditioners suction line is deteriorated or missing you can replace with foam insulation that can be purchased at your local home center or hardware store. Foam is resistant to deterioration caused by any condensation that may form on the surface of the copper tubing. Also, fiberglass insulation can breakdown outside if it is exposed to sunlight.

  • Use electrical tape to secure the insulation if it does not have an adhesive strip. You can also purchase special UV resistant line set insulation tape.

  • Be careful not to compress the insulation as you will reduce the thermal properties and ice may form at this point.
  • Protect any insulation from damage where it can rub against hard surfaces or be damaged outside from lawn equipment or pests.
  • When using slit insulation, place the slit side down so any condensation that does form can drain away from the tubing. If it is inside an enclosed or finished space, install the slit side up.

  • For small repairs you can apply adhesive foam or cork insulating wrap around the missing section.


Brian Crowther
Posted on Apr 4, 2013
carol roach
Posted on Apr 4, 2012
Account Deletion Requested
Posted on Apr 3, 2012
Donata L.
Posted on Apr 3, 2012
Jerry Walch
Posted on Apr 3, 2012
Sandy James
Posted on Apr 2, 2012
Francina Marie Parks
Posted on Apr 2, 2012