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Thread: Using a HVAC Condensate Pump or Directly Connecting to Sewer Line w/trap

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  1. #1
    DIY Senior Member DanMcD's Avatar
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    Jun 2005
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    Question Using a HVAC Condensate Pump or Directly Connecting to Sewer Line w/trap

    I like some advice on whether I should install a Condensate Pump for my HVAV or just have a plumber directly connect it to my sewer line and use a trap to prevent sewer gas from entering my furnace install. I am having my entire cast iron sewer lines replace with PVC, so I need to decide on how to do this correctly.

    Below is some background info on what I have now...

    My current furnace setup has the A/C & Humidifier draining directly into my 2 inch cast iron sewer line which is under my crawl space. It has been like that for 35 years and has always worked. When this was first installed, the HVAC person:
    (1) Connected the HVAC inch PVC to a inch piece of copper pipe.
    (2) He then bent the copper pipe to make a trap before it would enter my 2 inch cast iron sewer line. This 2 inch cast iron pipe is the drain for my laundry tub.
    (3) He then drilled a hole into the 2 inch cast pipe and connected the inch copper and added silicone caulk. FYI, the 2 inch cast iron pipe connects downstream to my 4 inch cast iron main sewer line.

    What is the best method/correct way to drain my HVAV?

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    All traps should be separately vented to prevent siphoning the trap dray. There is no guarantee that between the humidifer or a/c it will drain often enough to keep the trap that's there full.

    Most people either run it outside if there's no danger of freezing and it can be accommodated reasonably, or, dump it into something like the sump pump, or drain it into the top of the washing machine stand pipe.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Moderator & Master Plumber hj's Avatar
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    You can be ABSOLUTELY certain, that in the winter time, there will be ZERO condensation to keep the trap sealed, therefore the blower unit WILL suck sewer gases into the system and distribute them throughout the house. Either connect it to a fixture's trap connection or use a pump.
    Licensed residential and commercial plumber

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