In this short podcast episode, Bryan answers a question from Evan about the true cost of uninsulated refrigerant lines, especially in terms of efficiency losses and decreased longevity.

Insulation keeps refrigerant cold, usually in the suction line; it makes it harder for cool vapor refrigerant to absorb heat. (Expansion lines are also insulated.) When that refrigerant picks up heat, that heat has to be rejected again, and it makes the compressor run hotter, which can lead to premature failure. If an uninsulated or poorly insulated suction line is in an attic or crawl space, condensation may also form and cause damage, as the surface is below the dew point.

When suction vapor gets warmer, the discharge temperature, discharge pressure, and compression ratio all increase. The lower the compression ratio, the more capacity per watt; more BTUs move per watt input. The density of the suction vapor also decreases, and lower densities lead to lower compressor mass flow rates; that is where the efficiency losses occur.

Compressors are also cooled by suction gas, and when there is warmer suction gas, the cooling is less effective. The compressor will run hotter over the course of its life, which makes the oil less viscous and can lead to eventual oil breakdown. Technicians may also read a higher superheat on an uninsulated suction line and mistakenly add more charge to fix a classic symptom of undercharge. They may also misdiagnose a valve failure and perform an unneeded replacement.

Uninsulated suction lines are also code violations that will get written up on inspection reports, so we should address them as we see them and give the client a chance to accept or decline the insulation.

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