I have a sweating pipe in my ceiling from the AC. I have changed the filter and have tried to clean the coils the best I can. The pipes have no insulation around the sweating pipe.

Would this cause it to drip on the ceiling?

  • What kind of AC system is this? – ThreePhaseEel Apr 30 '17 at 3:02
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    Is there a large pipe and a small pipe running together or is it a single pipe, possibly a condensate drain line .Either way , the large lines would need to be insulated as Jim Stewart mentioned. – d.george Apr 30 '17 at 11:08

Probably this is the refrigerant gas return line to the compressor. It will be cold (maybe 45 or 50 F) and water vapor will condense to liquid water on it. It must be insulated and the insulation must be sealed or it will get wet between the pipe and the insulation. Keeping the line insulated will also make the a/c compressor work more efficiently and possibly last longer.

The gas return line is copper and will be the larger diameter line of a pair of copper lines which connect the evaporator unit (in the attic or in a closet on an occupied floor) to the condensing unit (compressor) outside the structure (usually on the ground).

If the evaporator unit is in the attic, then the line carrying condensed water may also be in the attic and this line may also proceed horizontally in the attic to and through an exterior wall and then terminate outside that wall where the condensate drips. The condensate line may be copper or may be plastic. This line will also be cold, but usually not as cold as the refrigerant gas return line.


The refrigerant gas return line (larger copper tubing) will be cold when the compressor is running, but will warm up to ambient when the compressor is off.

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  • When the condensate line is in the attic is it also insulated? My condensate line doesn't go into the attic but into the drain. If the condensate line is plastic it probably doesn't have to be insulated. Mine is PVC is not insulated and it doesn't condense water, but if it is copper it probably should be insulated. My evaporator unit is in a closet on the living floor of our one story tract house. The refrigerant lines go out to the condensing unit through a 4" or 5" diameter plastic chase under the slab. But the refrigerant gas return line is insulated. – Jim Stewart May 1 '17 at 15:18

Yes it will cause the drip in the ceiling.

The pipe must be insulated COMPLETELY, any place humidity can get to the pipe will cause condensation, collect in the pipe insulation and begin dripping again.

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