condensate drain

I'm selling a house where the indoor airhandler for the heat pump has a vertical condensate drain that runs thru the floor into the crawl space. It was installed that way new. Now, an inspector for the buyer lists that drain as a "fault" because it is not trapped. Does a vertical drain need to be trapped. I'm not going to replace it, but now I'm curious if the inspector's right or not. Pro AC tech opinion requested ( since I dare not ask this question on their newgroup).
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Curmudgeon wrote:

If it connects to a sanitary sewer, it needs a trap. That prevents sewer gasses from coming back in through it.
--
Joseph E. Meehan

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That I know...
So why do horizontal condensate drain lines from AC units have a trap bend? They connect to nothing but air. The only thing I can figure is to keep insects and the like from crawling into the unit. But again, a trap bend in a vertical line connected to nothing would make no sense...for either gas or insects.

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I found with my unit, that the condensate drain is on the pressurized side of the fan, this caused air to blow through the drain line, which in turn caused the liquid to be blown through the pipe. I put on a small trap to hold some water and it allowed the water to slowly drip through the tube.

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Its because there is negative pressure inside the air handler as opposed to atmospheric, due to air pressure drop through the cooling coil.
Without a trap, the drain simply sucks air into the unit, and so then the condensate collects all over inside the unit, overflows the drain pan and generally makes one hell of a mess whenever the fan shuts down.
The trap seals against this occurance and allows draining because it traps a water column of sufficient mass and at a low enough elevation such that this negative pressure cannot overcome and lift water out of the trap--remember vaccuum is often measured as "Water column".......together, this all allows the condensate to drain to the outside of the cabinet under gravity..........
--

SVL







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When I posted a question asking why my a/c condensate pan was overflowing I never got a satisfactory answer that I could use. I think you just hit the nail on the head. I am off to build a better trap (but not for mice)
Charlie
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Curmudgeon writes:

(1) Keeps air from moving through it, which is inefficient in itself.
(2) Air flowing through the pipe deposits dust and fosters clogging through microbial growth.
A "trap" in this case is a simple U bend somewhere in the run, usually at the air handler. Not a more elaborate trap fixture like on a sink.
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Hi Curmudgeon, hope you are having a nice day
On 10-Aug-04 At About 01:39:46, Curmudgeon wrote to All Subject: Re: condensate drain
C> That I know...
C> So why do horizontal condensate drain lines from AC units have a trap C> bend? They connect to nothing but air. The only thing I can figure C> is to keep insects and the like from crawling into the unit. But C> again, a trap bend in a vertical line connected to nothing would C> make no sense...for either gas or insects.
They are trapped if they are on the negative side of the air stream. if you didn't the water would never drain due to the air being pulled through the pipe.
-=> HvacTech2 <=-
.. "If you can't hear me it's because I'm in parentheses." - s.w.
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Hi Joseph, hope you are having a nice day
On 10-Aug-04 At About 08:36:56, Joseph Meehan wrote to All Subject: Re: condensate drain
JM> Curmudgeon wrote: >> I'm selling a house where the indoor airhandler for the heat pump has >> a vertical condensate drain that runs thru the floor into the crawl >> space. JM> It >> was installed that way new. Now, an inspector for the buyer lists >> that drain as a "fault" because it JM> is >> not trapped. Does a vertical drain need to be trapped. I'm not going >> to replace it, but now I'm curious if the inspector's right or not. >> Pro AC tech opinion requested ( since I dare not ask this question >> on JM> their >> newgroup).
JM> If it connects to a sanitary sewer, it needs a trap. That prevents JM> sewer gasses from coming back in through it.
Actually no it doesn't if you think carefully about it. I have changed many drains due to the fact they dry out in winter and cause a bad smell when in heating mode. you should never run a condensate drain to a stack or sanitary pipe.
-=> HvacTech2 <=-
.. "Its hard for me to buy clothes because I'm not my size."- s.w.
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Curmudgeon wrote:

Most residential air handler manufacturers require traps.
Code usually says something like this: "Condensate drains shall be trapped as required by the equipment or appliance manufacturer."
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It needs to be trapped. Most heat pump air handlers have the coil on the negative side of the blower. As indicated by other responses, air will flow from out to in and many times causes problems draining as well as the efficiency side effects.

We thank you for posting in the appropriate forum since many of us also read this NG for the very purpose of trying to help homeowners.
- Robert

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Thanks all for the replies. Sometimes logic just isn't enough. But it's been draining fine for nearly 20 years....the new buyer will just have to live with it working OK. :-)

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On Tue, 10 Aug 2004 16:09:19 -0400, "Curmudgeon"

..being the last man in on this one please allow the space to say this. Mostly the responses you got were 'right on the money',, granted I suspect the 'inspectoor' is most likely being plain bureaucratic when stating <mumble> must have a trap </mumble> and, well may it be that " it's been draining fine for nearly 20 years". However, I am quietly confident the unit has had some degree of inefficiency for that 20years (for the time it actually ran). That alone has already cost you dollars whether you acknowledge it or not. What I am also quietly confident of is that,, when the New Owner moves in, their use of the A/C will be different to yours. When that drain fails to do its job (internal flooding of the plenum) or the inefficiency of the unit is a cost worry to *them* A N D they discover you were *told* to fit a trap, then I would suggest your 'arse is grass'. You will pay in the long run,, so be a 'good lad' now and get down to the hardware and buy some elbows and pipe to make a trap from. Might cost you a whole $8.00US <g>
cheers
BTZ
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