How To Clean Out an HVAC Condensate Line

by Dave The Handyman on October 22, 2009

Hello y’all, Tampa Bay Handyman here today with some more home improvement tips for you, and today I will be going over HVAC.

Yes, the title may be a little misleading but that is what people are searching for – how to clean out your air conditioning condensate line, as the cooling creates the condensate that must be disposed of. When your A/C is not being used – moisture and crap will build up in the condensate line, creating a type of slime sludge. Once enough of this sludge builds up – it will restrict the flow of the condensate that is produced by the air handler, if this is left untreated the line will get clogged to where the condensate has no where to go. This will lead to two things. If you have a float switch installed on your HVAC system (which you should if it is new) it will trip the float switch killing the 24 volts to the thermostat – thus causing your thermostat, air handler and condensing unit not to function at all.

If you do not have a safety float switch installed – then the condensate will just overflow and flood your home. Bad shit. If a flood happens not only will that damage carpet, drywall, wood, etc, but that also brings on a bigger problem to deal with..MOLD! But that is a whole other can of worms that I have yet to open – it will be covered eventually…

The condensate line in most cases goes directly outside, although I have heard of some situations where it goes into sewer systems, I have never dealt with that though so I am going to assume that it is going outside of your home. If you see a pvc pipe sticking out the wall of your home somewhere, that is more than likely the condensate line. Now, the single best way to clean out a condensate line that I know of is with a nitrogen tank and the proper fittings, 3-400 psi of nitrogen will blow out nearly all of the slime sludge, but many people do not have access to nitrogen tanks, plus they are pretty dangerous – don’t worry, I have some alternate methods that you can use.

This is the one I use the most – a wet vac. The more horsepower it has the better. I recommend that you vacuum out the condensate line from the outside. If you want to take it a step further to ensure that it is free of slime sludge, dead lizards, snakes, or whatever the hell may get caught inside there, I recommend that you cut the condensate line right by the air handler and plug it off. You can use a PVC fitting cap, a rag, or your hand, or whatever to do so, but by plugging off the line you will get twice as much suction on the line. Just make sure that you have the proper PVC fitting so that you can reattach the condensate line. You can also do this the other way around by plugging the condensate pipe outside, and vacuuming from the inside, you know what I would do though, the choice is up to you.

Other ways to clean out an air conditioning drain line are with a garden hose with extremely hot water – this may or may not work, I don’t recommend it. There are also anti-slime tabs that you put in your air handler drip pan every couple of months that will prevent the growth of slime sludge. So if your air conditioning keeps shutting off and you have a safety float switch installed (most likely you do if it is a newer HVAC system), I would recommend using a wet/dry vacuum on the condensate line – you will save yourself a couple hundred bucks – which is what it will cost you if you call out an HVAC technician for a service call, as they have to make money too ya know.


{ 5 comments… read them below or add one }

bamalama June 6, 2010 at 10:01 pm

I would not recommend nitrogen or any type of compressed air. Speaking from experience, the pvc joints can blow apart, like places inside the wall. I’ve had this happen with $30K of floor damage in a kitchen. The cabinetts had to be removed and the entire subfloor replaced. Just my 2 cents.

R. Bennett July 17, 2010 at 11:11 pm

Condensate line sludge:
Like the article, my condensate line quit draining. When I cut a section of the line at the air handler, I found it was clogged almost entirely with a sludge which, for lack of a beter description, seems to be a kind of silt that you can break up into a fine particle suspension. I put in a shut off valve at the air handler with a drip leg below the valve. I can connect a garden hose to the drip leg and flush out the line without backflushing into the drip pan. I also used a large wet vac at the air handler and outside to both blow out and suck back any water in the condensate line. No matter what I do, the line seems unobstructed when usinf the force of hose or wet vac and fully obstructed when there only the 2′ water head which os difference in elevation between the air handler and the drain line outside. Water sucked out from either end of the line usually has a few visible pieces (maybe an eighth inch square a little thicker than a stamp) of sludge it.

Any suggestions?

patioplr October 12, 2010 at 5:17 pm

I just had this happen in my home for the 2nd time. The first time, the water backed up out of the floor drain in the basement where the condensate drains into. The next day, all the water had drained back into the floor drain. However, 2 days ago, it backed up again, and the water was not draining like it had before.

Finally called a tech and he said sludge had built up in the drain P-trap. He cleared it by relieving water from our water heater (which is right next to the floor drain). The hot water was able to melt and flush most of the sludge. He suggests doing this once a year. In doing so, he says if you drain your water heater completely, this will also remove some sediment from the water heater, improving system efficiency.

Joe April 28, 2011 at 9:16 pm

Great artical i would either use about 200LB of Nitrogen but if the drain gose to a a sink you better put a towel in there!

jason October 25, 2011 at 12:59 am

What do you think about a product called the diyvac ?We saw it on Youtube being demonstrated and seems to look pretty easy and effective to use.

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