I have two 2" PVC pipes running from outside (AC unit) to the inside set up (furnace?). I need to cut these pipes and re run them since they are blocking the water heater which I need to take out. I wasnt sure what they did so didnt want to cut them yet. Is there water in them? Do I just turn off the unit first? When replacing do I use just regular PVC pipe and glue or is the some flex pipe solution? Any help would be great. I added some photos.Blocking the water heaterInside the unitOutside

  • @Ecnerwal sorry I am not sure the technical terms since I dont do HVAC. The pipes run from the outside unit (air conditioner) to the inside unit (furnace?). – Packy Aug 4 '15 at 18:40
  • which pipes are you referring to? I see condensate drain (white), heating loop, gas, ... and maybe direct-vent intake and exhaust. Plus water plumbing. – keshlam Aug 4 '15 at 18:51
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    Not an expert, but pretty sure these are air intake and exhaust for the furnace, especially since they run outside. – DarthCaniac Aug 4 '15 at 19:00
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    Yes, direct vent intake/exhaust, judging by the connections shown in second photo. If so, one is exhaust fumes; you do(n't want that leaking and definitely don't want it open while furnace is running. – keshlam Aug 4 '15 at 19:11
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    Yes, the outside makes it very clear. Make sure the furnace is off and cut them out as needed. I'd then replace with the same (looks like ABS). Reroute as needed. – DA01 Aug 4 '15 at 19:22

OK. These have nothing to do with and no connection to the AC compressor, which makes a lot more sense than the original question with no outside picture.

Flex pipe is probably not an option - if it IS an option it needs to be a type specifically approved by the furnace manufacturer.

While direct vent exhaust is relatively cool, so it can be run in plastic pipe, it is still quite deadly due to the carbon monoxide it contains, and you do not want to be casual about how it's handled, or you and your family won't wake up some day. It happens.

You might well plot out a different route for the pipes that is less inconvenient, but be sure it fits the manufacturer's requirements for the intake/vent system (or have it done, or checked, by your heating contractor.)

  • Thanks. Not sure why they blocked in the water heater, but I will just do hard lines again. To do this safley do I just turn off the AC and furnace before cutting them? Then just use the same PVC pipe and re glue them – Packy Aug 4 '15 at 19:23
  • @Packy Check the pipe carefully for printing- I think you'll find that DA01 is right and it's ABS, not PVC (different type of glue, and couplings) - actually, that can in fact be read in the first picture at full size. – Ecnerwal Aug 4 '15 at 19:31

Those are acrylonitrile butadiene styrene (ABS) pipes, and can indeed be replaced and/or rerouted.

When assembling the plumbing, you'll want to use fittings and cements designed for use with ABS pipe. You'll also have to refer to the manufacturer's installation instructions for proper length and limitations on the number of bends.

For reference, the pipe that enters higher on the unit is the intake. It brings in air from outside, to be used for combustion. The lower pipe is the exhaust, which carries harmful combustion byproducts outside.

While you complete the work, you'll want to insure the unit does not run. The best way to do this, is to turn it off at the breaker.

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