HVAC systems utilize piping to transfer cool/cold and warm/hot fluids to ultimately deliver conditioned air to a building’s occupant spaces. 

The cool/cold line is known as the suction line or ac return line. It conveys fluids, such as refrigerants, at temperatures of about 40°F [4.4°C]. The liquid line conveys warm/hot fluids at about 110°F [43.3°C]. Finally, the discharge line is typically very hot and operates at about 150°F [66°C].

AC return lines should always be insulated when their operating temperatures are below the ambient temperature to prevent condensation and heat gain to the refrigerant. 

Although liquid lines are warm/hot, they should be insulated in spaces where the ambient temperature exceeds the liquid line temperature such as an unconditioned air plenum or attic. When personnel safety is a concern, insulation should be added.

Discharge lines are not typically insulated, however, they should be insulated when personnel protection is of concern and heat loss would not be desirable for the given application.

Closed-cell elastomeric foam pipe insulation, also known as rubber, is a preferred insulation type for ac return lines due to its closed-cell structure with a built-in vapor retarder. When the proper AC return line insulation thickness is selected, closed-cell elastomeric insulation effectively controls condensation while preventing heat gain. 

Unlike some other insulation types, closed-cell elastomeric insulation does not require a supplemental vapor barrier unless it will be subjected to extreme conditions (high ambient temperatures, high relative humidity, very cold operating temperatures, solar radiation) or mechanical impacts (foot traffic, extreme weather, birds).

For ac return lines exposed to UV exposure, such as roof-top applications, closed-cell elastomeric insulation should be protected with the manufacturer’s specially-formulated protective coating or an insulation jacket.

Aeroflex USA’s Aerocel® brand of EPDM (ethylene propylene diene monomer) closed-cell elastomeric insulation is available in preformed unslit, factory pre-slit (SSPT™) and continuous tubes to effectively insulate ac return lines.

Aerocel is designed to control condensation and heat loss for continuous operating temperatures of up to 257°F [125°C] and is safe for use on copper, aluminum, and stainless steel piping. Additionally, EPDM offers durable UV resistance when compared to traditional NBR/PVC rubber. 

To learn more about AC return line insulation, visit https://www.aeroflexusa.com/epdm-pipe-insulation-benefits