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Old 08-05-2013, 02:03 PM   #1
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A/C condensate plumbing

What's the best practice for draining A/C condensate in a system that already has a lift pump for the 95% furnace condensate?

I have an upflow furnace with coil on top, so the coil drains are under slight pressure. I'm assuming the drains should be trapped so they don't function as air leaks.

Do I put unions as close to the coil as possible so pipes can be removed for cleaning, trap both primary and secondary, run primary into the lift pump and leave the trap outlet on the secondary in the open?

How do I keep the secondary trap from drying out?
Should the end of the secondary drain line be pointing up so a little water can be poured into the trap on occasion?

Is it better to make a trap in the primary line or just run it below the minimum water level in the pump reservoir?


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Old 08-05-2013, 06:26 PM   #2
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A/C condensate plumbing

In my experience traps plug up with bacteria and damage more furnaces than they are worth. the small amount of air leakage is not worth the trouble. there are a dozen ways to drain it but my KISS method and what I use on mine is:

Go to HDepot get a 3/4" galv tee and nipple and barb fitting adaptor to fit a clear 3/4" plastic drain hose they sell by the foot and drain it into the top of the pump. put a 3" tee on top also. that way when you want to clean the drain port you pop the hose off and clean it in 2 mins and Bobs yer Uncle. Gluing PVC looks pretty but has to be chopped to clean. I don't use the secondary drain unless it is in an attic. If you clean it once a yr it should not plug up or need the secondary. I am sure other guys do it different but the KISS method is my choice and HDepot has the stuff 4 U.

You may get away with a 3/4 elbow and no open tee BUT you have to watch it very carefully for the first hour to see if it drains properly. sometimes the air velocity is so high across the coil it needs that open tee to siphon properly. mine works fine with a elbow and clear hose so I can see the draining action/flow.


"Cut it twice and it is still too short".

Last edited by yuri; 08-06-2013 at 07:14 AM.
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Old 08-05-2013, 10:40 PM   #3
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A/C condensate plumbing

this is what I use
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