Drain Cleaning Protocol

This article is primarily based on HVAC School’s “Drain Cleaning – More To It Than We Think,” hosted by Bryan Orr and featuring Corey Cruz and Mike Klokus. You can listen to that episode HERE.

How hard could it be to clean a drain? The slime should just wash away if you flush the drain with water or blow some nitrogen in it, right? That’s one approach to take to cleaning drains, but it’s not a very good one. Simple work (or straight-up laziness) comes at the expense of callbacks and harsh Yelp reviews.

Proper drain cleaning is a commonly overlooked element of the trade. It may sound like a simple task, but many drains are not properly cared for. Customers may not know that they have a gunk diorama of the Hoover Dam in their drain pans, but they will notice that something’s wrong. That’s where you can come to the rescue.

Here are some proper drain cleaning protocols that can prevent a lot of heartache and time-consuming callbacks.


Clean more than just the drain line

When most people say “drain,” the drain line is what comes to mind. While it is important to clean a drain line, several other parts need attention, too.

You’ll want to remove the panels on the air handler or case coil. That way, you can access the drain pan and clean it. It’s easy for debris to build up in the drain pan. Even though a quarter or half-inch of grime doesn’t sound like a big deal, it’s going to block fluids in the drain pan. It's like a gunky dam, and it's not good for the system.

We recommend checking the status of the filter, evaporator coil, and condensate safeties as well. These are especially critical for horizontal air handlers and during the summer (when the unit will spend most of its time cooling).


Use small brushes to clean coils and narrow channels

We love using shop vacs to clean drains. Unfortunately, they have their limitations. One of those limitations is size. They can suck the sludge out of larger areas, but you’ll have a hard time making headway on small A-coil channels with a shop vac. We recommend using small brushes or even wires to clean areas that are hard to reach with a shop vac.

You can make a small set of vinyl tubing tools to attach to some PVC and a shop vac. Vinyl tubing allows you to see what you’re sucking up, so you can tell if you’re making progress. You can also reach those channels with bottle brushes (or zip ties and thermostat wire). When you use those materials, you may want to run water while you clean those small channels. Water will force all the buildup to the front while you work.

Grime builds up quickly in small channels and coils. Thoroughly cleaning them will spare you trouble later.


Take note of the drain’s setup within the unit

Before cleaning a drain, you will want to analyze the drain and its parts. Consider the setup of the air handler, fan coil, furnace, and case coil. See if you can answer the following questions about the unit:

  • Where will the water come out?
  • Will the water flow into a drain pan or float switch no matter what happens in the case of a backup or other issue?
  • Are the float switch and secondary pan firmly set in place so they won't move or slide?

It's vital to ensure that everything is anchored in place and able to handle the weight of the water. The drain setup’s structural integrity will affect the drain’s function, so it’s always a good idea to check that the drain can handle overflow and perform its necessary job.


Consider if you’re working with a communal (common) drain system

In communal (common) drain systems, several HVAC units lead to a single common drain. A backed-up common drain will have a different set of consequences than a single obstructed dedicated drain. More drains will be affected by blockages, and they will suffer the consequences of careless cleaning practices.

If a common drain backs up, several units are at risk of leakage. Also, you have to make sure that you clean dedicated drains without messing up other people’s drains. You have to be extra careful of backflow if you’re cleaning a single dedicated drain within a communal drain system.

The drain size is also an important thing to note when dealing with communal vs. dedicated drainage systems. It varies between dedicated and communal drain systems. Dedicated drains are usually only about ¾” wide, while communal drains can be around 2” wide.

We also strongly recommend considering where the condensate will come out when working with a communal system. If the drain leads out to a garden, you may not want to dump chemicals in the drain pan!


Assess the benefits and drawbacks of each cleaning technique

We recommend using one of the three main techniques for cleaning a drain. These are using a shop vac, compressed air or nitrogen, and water.

We have already talked a little bit about wet/dry vacs. They are versatile and portable tools, but they have their limitations. We have already said that they’re difficult to fit into small spaces, but they are also on the weak side. Their suction power is limited to 14.7 pounds of force per square inch by physics (and you obviously get a lot less than that).

Compressed air or nitrogen is a bit stronger than a shop vac, but you must be more careful with it, especially in communal systems. You can cause leakages in nearby drains if your compressed air messes up the piping. That is especially problematic if the drain system runs through a wall. If you want to use compressed air, it would be best to be mindful of your blowing power and the drain system’s structural integrity. Cap vents properly, and make sure fittings are glued before you blow compressed air into a drain that leads to a common drain.

We believe that pressurized water is the best solution. It's powerful, clean, and less likely to cause problems in communal systems than compressed gases. Unfortunately, you won’t always have a hose at the ready and may need to consider other techniques when water is unavailable. You also have to be careful not to let the water overflow into the return or make a mess in general.


Do your homework on chemicals

Chemicals are a decent supplement to other cleaning techniques, but we do not recommend using them on their own. Chemicals are most effective when they are diluted to the manufacturer’s instructions and allowed to sit in a single spot and work their magic.

You also have to be mindful of where the chemicals go. As I briefly mentioned earlier, you will want to avoid using chemicals if the drain lets out in a place with plants and personal property. Some sewer systems cannot handle certain chemicals, so you should make sure the drain line either leads to a safe outdoor location or that the sewer/septic can handle the chemicals you use.

If you want to add chemicals to your treatment routine, we recommend using Refrigeration Technologies products. Their Viper Pan & Drain Treatment is a great addition to your drain cleaning toolbox.


Recognize zoogloea buildup and treat it

People have developed several names for the infamous white slime that blocks their drains: elephant snot, the Florida condensate snake, you name it. No matter what you call it, bacterial zoogloea is a problem that has only gotten worse with the widespread usage of aluminum coils.

It helps to understand what causes zoogloea. The slimy residue accumulates very quickly and relies on environmental conditions for development. It's especially problematic in humid climates.

Introducing copper to a drain line will help solve a zoogloea problem. Copper in a drain creates ions that serve an antibacterial purpose. Copper and some other metals, like silver, are also useful against fungi and viruses.

For more information on preventing and treating zoogloea, check out this video on bacterial zoogloea.


Prime the drain and watch

We suggest priming the drain pan by pouring water directly into it. When you do that, you simulate water coming off the evaporator coil and fill the trap to confirm that the pitch is correct.

You can consider going outside and making sure the water runs consistently. When the stream is constant and steady, you’ll know that there are no more blockages. When there are uneven spurts of water, then you’ll know you have another problem. It would also be wise to leave the unit running after you finish the cleaning job. That way, you can see if it drains by its own power.


Check airflow to keep the big picture in mind

Airflow efficiency and drainage may not seem to be that closely linked, but you’d be surprised at the issues that high static pressure and high coil air velocity can cause.

Whenever you have issues with intermittent drainage, popping sounds at the drain, or water blowing off the coil or out of the pan, check your static pressure and air settings.

A double trap may also be the culprit of these problems. Double traps impede drainage because air gets caught between the traps and prevents drainage.

On that note, don’t cap vents if you’re not actively cleaning a drain! Cleanouts get a cap; vents (after the trap) do not.


Cleaning drains may seem like gross, mundane work, but learning to clean a drain properly is an invaluable skill. Even though there is a lot to consider when cleaning a drain properly, your customers will thank you for your careful work. By that, I mean that you’ll deal with far fewer callbacks! There is no better reward for a job well done.

If you want to learn more about drain standards and best practices for disposing of condensate, you can read this article on Condensate Drain Codes and Best Practices.



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