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Thread: Condensate Line to Sewer Pipe, NSPC

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    DIY Junior Member PrezMFL's Avatar
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    Default Condensate Line to Sewer Pipe, NSPC

    Hi everyone, I was searching the internet for some advice and found this site and was hoping you guys could help me out. A little background...I bought a house last June and this past winter I woke up one day and saw a wall with water damage. Turns out my condensate line from the furnace/AC unit that terminates outside froze causing backup into the house. Had a plumber come out and give me an estimate to relocate the pipe inside so it won't freeze. He suggested connecting it to the sewer pipe and using a trap to prevent sewer gas from backing up. Sounds scary to me! Talked to a home inspector friend of mine who said he wasn't crazy about the idea (but has seen it done plenty of times), what if the water in the trap freezes (it's in my attic) then I would have a backup of gas.

    I just want the problem taken care of and am tired of worrying about it. Since it is in my attic, I don't have much choice where to relocate the drain. Any help or comments would be appreciated, thanks!

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    Forum Admin, Expert Plumber Terry's Avatar
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    I would trust the plumber.
    They are licensed, which takes 8,000 hours before they can get their card, have to pass a State test, and have education credits.

    Sewer gas in the attic? Is your attic ventilated? Mine is.
    But never mind, plumbing vents extend through the roof so that the smells don't get trapped.
    You could put insulation over the pipe to trap the heat in.
    It's a lot warmer "in" the attic then it is outside.

    He could also find a sink or lav inside the house, cut the wall and add a trap and funnel for the condensate.

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    Moderator & Master Plumber hj's Avatar
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    I assume this condensation is from the flue, because there is NO condensation from the furnace A/C unit in the Wintertime. There are situations where the furnace CAN and WILL draw sewer gas into the building if this is the A/C condensate line.

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    Master Plumber-Gas Fitter shacko's Avatar
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    they certainly do produce condensate. Where do you think the term high efficiency condensing furnace comes from?

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    DIY Member Lightwave's Avatar
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    Both condensing furnaces and AC coils produce condensate. Both produce condensate only when they are operating: AC in summer, furnace in winter.

    The condensate line on a condensing furnace is connected to the combustion air/flu piping. Because condensing furnaces have a sealed combustion air path, the condensate line has no connection to air inside the house.

    AC condensate lines are directly connected to house ductwork and must be appropriately trapped all year or protected by an air gap. Do not drain AC condensate into DWV piping without ensuring that the trap will remain filled all year. Failure to do so will cause sewer gasses to enter the house.

    Specific requirements apply to trapping draw through AC equipment where the AC coil is on the low pressure (draw) side of the blower. Air handlers are the most commonly found draw through AC equipment. Follow manufacturer instructions or refer to this document from Lennox. Failure to adequately trap draw through AC will prevent humidity removal, could cause water damage to the blower, and will result in sewer gas being drawn into the ductwork by the blower.

    Secondary drain lines must be installed (and trapped) on HVAC equipment installed in an attic or where water leakage could cause damage.

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    Moderator & Master Plumber hj's Avatar
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    Which is WHY I said I assume the condensate is from the flue. But that would require that it be a condensing unit, and that may, or may not, be what the person has. He does not specify, so we are just guessing.

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    DIY Junior Member PrezMFL's Avatar
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    Sorry, I am not sure what type of unit I have in the attic. I was hoping to have another plumber out and see if the can find anywhere else to place the line. I am not comfortable with it being attached to the sewer pipe.

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    Moderator & Master Plumber hj's Avatar
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    Where the condensate line attaches to the air handler will tell what kind of condensate you are draining.

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    Forum Admin, Expert Plumber Terry's Avatar
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    I've plumbed in plenty of drains in super markets for condensate drains.
    All the freezer cases need them. It's all connected to the waste, which goes to the sewer as it leaves the building.
    They have p-traps to prevent sewer gas from entering the store, and the condensate is constantly keeping the p-traps full.
    They've been plumbing it this way for decades.
    What makes your house different from the one next door?

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    DIY Member Lightwave's Avatar
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    The difference is that residential AC equipment and furnaces don't produce enough condensate to keep their respective traps full all year.

    AC condensate will keep the AC trap full in summer, but the trap will dry out in winter and allow sewer gas into the house. Been there, have the sewer gas exposure to prove it.

    Furnace condensate will keep the furnace trap full in winter, but the trap will dry out in summer and will allow sewer gas into the flue.

    You need an air gap and a full trap between condensate drains and the sewer. You can't meet the full trap requirement in an attic without installing a trap primer.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Then why wouldn't they just throw a trap primer on it?

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    Moderator & Master Plumber hj's Avatar
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    Dollars, and unreliability. Here, the AC condensates are either run to the washing machine drain box, or to a branch tee in a sink drain. Also, here, freezer condensate lines are ALWAYS extended out of the box and to an indirect connection at a floor sink outside where it will NOT freeze.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Most of the condensates in home I've seen have been to the washer.
    The fact that the onsite plumber didn't suggest that, I was thinking distance may have been an issue.

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