How often do you need to run a bleach and water solution through the condensate drain lines (of a heat pump) to keep the bacteria away?

What are the recommended parts (e.g. 1 part bleach, 10 part water)?

  • Do you mean to clean the coils? – tooshel Aug 2 '10 at 20:36
  • What "lines" are you referring to? (Hopefully not the coolant lines...) – myron-semack Aug 2 '10 at 20:38
  • No, the heat pump has a drain line. You have to clean it out.. just not sure how often or with what type of mixture. It drains outside through a PVC pipe – Brian Aug 2 '10 at 22:28
  • VINEGAR NOT BLEACH....sorry for the caps but that's better than bleach according to the old timers down here in Florida....bleach hardens the PVC, vin don't... – user61817 Oct 26 '16 at 0:50

I tend to pour a cup of bleach down the line once a month. Without that at least in Florida you WILL get an algae backup in the line, which if you have bad overflow sensor can cause all kinds of fun water problems.

If it is already blocked, just pour the bleach and let it sit. Eventually enough algae will die and the block will clear itself out.

  • Thanks I have a float valve, at least that's what they called it, so that if it overflows due to blockage then it cuts off the unit. It's not blocked now. I ran half cup of bleach, waited five minutes, then ran a cup of water through the unit. Should I run another cup of water over the next couple days just to be sure? – Brian Aug 3 '10 at 14:09
  • Its not really necessary. Just check that when your A/C unit is running that a steady drip of water comes out of the drain. Side note: Don't always trust the float valve... I had a bad one and got the joy of water pouring through my ceiling. – chotchki Aug 3 '10 at 14:18
  • Thanks for your input. My air handler is in the garage. The entire system is only about 4 months old. – Brian Aug 3 '10 at 14:36

Based on the comments, I think you are talking about the condensation line from the air handler.

For the condensate, you shouldn't need to worry about bacteria. It's not like you are drinking from it, and it doesn't form a pool of stagnant water in your system (unless it is plugged).

You do need to worry if the condensation line gets plugged up, however. If so, it will back up and flood your basement/attic (wherever the air handler is installed). On a humid day, the system can extract quite a bit of water from the air. You don't want that on your basement floor.

The water that drips through the lines is condensation, and therefore very clean. The water won't have any crud in it to deposit in the line. (Unless your air handler is filled with dirty air, then you have bigger problems.)

Depending on where the other end of the condensation line leads, this might be a more likely entry point for dirt/scum. If it is outside near the ground, mud could splash into it, bugs could crawl into it, etc.

Probably the easiest thing to do would be to attach a Shop Vac to the far end of the line and let it suck. You could also use an air compressor to blow out the line from the inside.

Another option would be to pour some diluted drain cleaner (Draino) into the line, and then flush it out with the hose. Make sure you flush it throughly. You don't want the cleaner to sit in there and eat the pipe.

Cleaning the condensate line shouldn't need to be done often. Once a year at most. Most people probably never clean theirs.

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    if you live in florida, this is bad advice. a condensate line in flordia WILL develop alge in the summer because the water flow just isn't fast enough to flush out the microbes, especially if you have a long horizontal run or the equivalent of a p-trap. – longneck Jan 13 '11 at 19:59
  • But if you live in Chicago, basically never. – Mazura Oct 26 '16 at 3:29

It only really needs to be cleaned if it becomes blocked or restricted, if you notice a build up of algae or other such grossness you can flush the line with a 16/1 water bleach mix (making sure you clear the blockage first). After the water bleach mix I would flush the line again with straight water a day or two later, just to make sure the bleach and whatever it cleans is cleared out.

As for how often. It really depends on your situation, keep an eye on it and if it starts to build up flush it again before it becomes blocked. If you find yourself cleaning it often (more than once a year), you may want to do some investigation to find the underlying cause.


From an A/C engineer....

Personally I would never pour bleach into any part of an a/c system. You can purchase antibacterial coil cleaning solutions specifically designed to do the job. The heat exchanger is formed from copper and coated with aluminium fins, these can be corroded in harsh environments like near the sea side, even environments where vinegar is present. I dread to think what damage bleach will cause..

Pay the experts to do what they do best.

From experience in dealing with customers who try and save a few pennys by doing everything on the cheap, it always ends up costing alot more in the long run.

Don't be so mean...................................

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    You know this is the DIY section of Stack Exchange, right? – RQDQ Oct 9 '12 at 20:28
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    Ah yes, the AC Contractor Mafia, sowing fear to keep DIYers at bay. – Doresoom Mar 11 '14 at 19:35
  • No one is suggesting you clean the coils with bleach, only the condensation drain line. – draksia Aug 7 '14 at 13:07
  • I upvoted because of the copper and aluminum corrosion point and the suggestion to buy cleaners for this specifically instead of bleach. I think anyone can clean a drain line, but I also think that you should pay $10 for the proper cleaner. – Zach Mierzejewski Apr 4 '16 at 21:19

I moved into a new house in upper Florida, almost to the Alabama border and when I had problems with my air conditioner I called someone to come out to fix it. The maintenance guy told me I should be running 1 cup of straight bleach through my PVC pipe that goes to the air conditioner monthly.


I have experienced several types of residential HVAC draining systems. The most common is a basic, gravity run. A simple line that runs down hill from the condensate pan until it exits the residence and drips onto the ground. The other system I have seen involves a gravity fed line from the condensate pan to a reservoir that has a float, switched pump in it that pumps the condensate when it reaches a certain level out of the residence via a line that then drips onto the ground.

I have lived in the south eastern USA my entire life, from LA,GA, To TX, and almost every home that I have lived in has had a clogged drain line at some point. The mass looks like the algae mats that grow in ponds and persistent puddles(none of those here in SA TX!). Once or twice a year, either the HVAC unit runs in short spurts or shuts down depending on the sensors and switches built into each brand/model of interior and exterior units or more often it isn't effective as normal at removing moisture from the air or heat.

Some systems have drain blockage sensors that determine when either the pan is overflowing or the drain is blocked. This usually mean that moisture is getting somewhere it shouldn't. Some HVACs beep, some flash lights, some turn off, you need to consult field reference information on the model you have. In a float pump based system the blockages can occur in a few different places. The PVC line that runs from HVAC to pump reservoir. The pump reservoir itself, or the line to the exterior.

I find that the hottest water I can run from the tap and household bleach to be the most effective method dissolving the algae clumps and not damaging the plastic/copper system that is in place at my current residence. I run the hot water and bleach mixture through either the pump or the pvc tube depending on where the blockage is. I use flashlights and strategic placement or an assistant to inspect the pipes, that along with a process of elimination lets me know where the problem is.

My pump has a different pitch to it when there is algae in it so that also makes it easy to pinpoint reservoir algae. Once the lines are clear, I put the bleach and the funnel that I never remember to use to regularly sanitize the lines and keep them clear. After that I resolve to add a cup of bleach once a month. Then I completely ignore the HVAC except for the occasional way past due filter change until I notice a difference in temp, humidity, or sound and then trouble shoot again.

I usually promise myself a good splash of bleach at the top of the pvc once a month. Measured in a few seconds of pouring into a funnel. I wonder if there are mechanically timed drip systems to add the bleach to the line constantly to get the most even application.

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    Giant walls of text are difficult to read. Consider adding some paragraph breaks, photos, or markup. – Tester101 Aug 5 '14 at 13:02

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