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Condensate drain line installation for minisplit head units when the refrigerant lines come from above the head unit

artisanfarms | Posted in General Questions on

I’m looking for tips and tricks for condensate drain line installation for head units when the refrigerant lines are run thru the attic above the head units.  

The options I’m seeing are:

1) Run condensate lines in PEX to the basement drywells.

2) Tie into the DWV lines with a trap in the condensate line (I don’t like this idea because I am concerned about the trap drying out when the unit isn’t used for a long period and the line becoming a vent)

3) Run outside the building at rim joist height (my concern here is in the winter I may occasionally  have drifting snow above the rim joist)

Are there other options?  What have other people done?

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  1. Expert Member
    BILL WICHERS | | #1

    You have to air tap the connection if you drain to a sewer line. There are special fittings made for this purpose, some of which look like very small sinks. You are not supposed to plumb directly into a sewer line and then put a trap in the condensate line — the trap goes BEFORE the air gap fitting or fixture.

    I would not run the condensate lines outside of conditioned space unless you’re in an area where freezing is never a concern. I’d run the lines in the walls, then do either a storm water drain (if available), or one of the air gap arrangements to drain into a sewer line.


    1. DC_Contrarian_ | | #6

      Bill --

      I think you're thinking of data centers which cool year-round. Residences don't typically run cooling in sub-freezing weather.

  2. DC_Contrarian_ | | #2

    If you use a condensate pump you have more flexibility in how you run the condensate lines.

  3. maine_tyler | | #3

    artisan farms,
    I'm no expert on this, but the recent install I had done included a ceiling unit in the attic. The condensate line runs up for a leg, then is pitched in the attic to join with the line sets and runs down the exterior wall. I assume a pump is used as DC says.

    Is freezing condensate a concern given that it's usually generated when in cooling mode? All the installs I see here in Maine, where it undoubtedly gets below freezing, runs condensate lines to outside.

  4. Expert Member
    Akos | | #4

    Around me (Toronto) condensate lines are universally run outside down to grade in retrofit situations.

    Much better option is to run it into an existing plumbing fixture. Good spots are a standpipe for the washing machine, a floor drain, overflow of a tub or into the tailpiece of a sink. The standpipe and the tailpiece tends to be the easiest. Oatey even makes a condensate adaptor for their washing machine rough in boxes. Any of these connection have a P trap afterwards so you can run the condensate directly into it with an air break.

    No matter where you run the drain, do not use the corrugated flex pipe sold with most mini splits. These are evil, they tend to sag and which can trap water and are quick to clog. I like either irrigation black poly pipe or pex.

    1. Expert Member
      BILL WICHERS | | #5

      Black poly pipe has the additional advantage of being less likely to grow algae inside if it’s in an area exposed to light. I’ve had that problem before with clear vinyl condensate lines.


  5. walta100 | | #7

    Some heads there are optional kits for condensate pumps the fit inside the head so the line can follow the others.

    If you drain to the plumbing they sell “trap primers” that slowly drip water to keep the trap full.


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