310.1 Condensate Drains:  Understanding the Codes

310.1 Condensate Drains:  Understanding the Codes

Correct Installation of Condensate Drain Lines

Residential HVAC installers have to understand so many facets of the construction industry.   In this blog, we’ll be talking about the importance of installing condensate drain lines correctly so the system doesn’t cause damage to your customer’s home.

I’m not here to pretend I know or could even interpret all the codes correctly.  In this series of blogs, I’m simply trying to open a conversation about codes we cite on the job every day out there without even knowing it.

What the Mechanical Codes Say

Let’s take a look at what the codes say about condensate control and adherence to the code when doing an HVAC change-out.

IMC 307.1 and CMC 310.1 talk about condensate from the cooling coils we’re installing in people’s homes.  They both say pretty much the same thing.  Condensate from air cooling coils and the overflow from evaporative coolers and similar water supplied equipment shall be collected and discharged to an approved plumbing fixture or approved disposal area.

Examples of “approved areas” include a trapped and ventilated receptor to a sanitary sewer, and a downspout that terminates to an approved area.  The most popular areas we terminate condensate drain lines to is the side of the house and usually about six inches from the ground.  And this can be in a planted area that is large enough to accept the amount of drainage, and soak down into the earth.

Public Walkways

Another important topic is covered by the code books and installation manuals for the equipment being installed.  We cannot have condensate runoff drain to public walkways and driveways.  This creates a nuisance area of slippery water that, over time, can even start creating algae which are even more slippery.  That’s pretty much common sense, right?

What about the sidewalk on the side of the customer’s house?

It may not be defined as a “public walkway,” but it would still be a nuisance for the homeowner and family members who must walk through that wet spot every day during normal activities.  We like to create a “French Drain” thereby using a roto-hammer.  We make a three-inch hole in the sidewalk and bore all the way through the 4 to 6 inches of concrete and fill it with pea gravel.  This allows the water to drain to the side of the house, down through the gravel and into the earth down below it and keep the sidewalk dry.

The inspectors say we if we discharge the condensate into the house’s actual drainage system, it must be by means of an indirect waste pipe.   And to clarify that, an indirect waste pipe is something upstream of a trap rather than downstream, and this includes the main venting stack as well.

So, if we are supposed to drain the primary into the drainage system of the house, can we terminate the drain line over a gutter and let the water fall into the gutter, where it will continue to the ground to an approved area?  CMC 310.3 says condensate waste pipes must be made from materials designed to work with that type of condensate drainage.

Why would we be worried about draining our condensate liquid into the rain gutter?  If the drain line includes waste from a condensing furnace, it will create a more acidic waste type that needs to make it to the ground. Thin aluminum rain gutters were not designed to carry this type of corrosive waste to the ground.  They will eventually rust out and create a new problem.

The Termination Point

The means by which the condensate waste is delivered to the termination point is as important as where we discharge it.

We have to use certain materials for our piping.  We have to use an approved corrosion resistant pipe like Schedule 40 PVC.  That’s the most popular type of piping HVAC installers use today, but we can also use ABS, cast iron, or hard drawn copper.

And that piping needs to have a certain slope to it.  That’s why we call it a gravity drain because as long as we have the necessary 1/8 inch of downward slope for every 12 inches of carry, gravity will do all the work and pull the condensate waste to the ground all by itself.

Maintaining the Drain Line Slope

A point I want to make to installers:  we can get caught up in this little 6 by 4 area we’re installing in and not be mindful of the complete drain line. One thing you should prove to yourself if you’re the one installing or modifying the current drain line, is to make sure you get a level on it.  If the condensate lines travel off the service platform and disappear in the insulation, that’s fine.  But you still need to confirm to yourself that the ENTIRE drain line has at least, an eighth-inch slope to it.

I’ve seen some pretty big dips in PVC piping which clogs the drain line, creates a backup, and causes water damage in the house.

Maintaining Alignment

You’ve installed the new system and now that you’ve adapted into the existing drain line, you own the whole drain line.  You won’t be able to say, “well, I just joined into it right there and thought the rest would be okay!”

It’s not too much to ask for, and the inspector can cite you on the fact that you may have slope in certain sections of your drainage but if the workmanship of the installed drain line is all cattywampus, the inspector can ask you to re-run it more uniformly.  The idea here is to maintain straight alignment, a uniform slope, and strap or support the drain lines at proper intervals as guided by the installation manual and code books.

The Proper Interval to Support PVC drain lines

We’re required to get a strap on it every four feet.  Whether its to support the drain line with hangars, or to strap it down to the deck, we don’t want the PVC to bow downwards, creating a dip and not allowing gravity to do its thing.  When we are mounting to the deck, I use cut-off PVC piping to create stanchions, and reinforce the downward grade, off the service platform.  This gives your drain pipe a uniform look and makes it easy for the inspector to pass your job.

A little further up the drain, toward the evaporator coil, the question is, do we have to install a p-trap or not?  When it’s required by the manufacturer’s installation instructions, Sacramento area county inspectors look for a trap.  Trane, our old supplier, saying “a field fabricated trap is not REQUIRED for proper drainage due to the positive pressure of the furnace; however, it is recommended to prevent efficiency loss of conditioned air.”

Setting up a System for Success

At the very least, a cleanout is required by code.  310.3.1 basically says it’s not reasonable to ask a future technician who has to come out to clear a blockage, to cut the PVC lines in order to do so.  And I see far too many systems without a cleanout on them.  This mandatory cleanout allows technicians to blow-out the lines with compressed air at a later date when mold and gunk build up inside it.  And trust me, it will!  This is just another prime example of how installers can set a system up for success down the road when another technician comes to service it.


As far as sizing goes, we use 3/4 inch Schedule 40 PVC drains for all residential HVAC.  Anything over 20 tons uses larger diameter piping.  We only get up to 5 tons in people’s homes.  The code book says the size of the pipe is for one or a combination of units, or as recommended by the manufacturer.  Make sure to check the installation manual if you have two systems.  If you’re planning to tie two evaporator drains into one single drain line, they may want you to increase the size of the final pipe going to the outside.

A Final Word of Wisdom

There’s one final little touch I’d like to pass on to you.  Be mindful of the lettering on the PVC piping.  An old foreman of mine always liked to glue in his PVC with the lettering facing away from the perspective of the person sitting on the platform.  I never stopped doing it that way again because it looks clean.  There’s less busyness going on in the scene.  Little touches like this can make the difference between a clean install and an average install.

Looking Forward

Wow, this blog got a little long!  We’re going to have to tackle secondary condensate drainage on another video.  But I hope this answers some questions you have about the building code, HVAC installations, and condensate drain lines.

Don’t forget to check out our YouTube page.  We have all kinds of great videos about your home’s hvac system.  And check out many related blog posts here.

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Thanks so much for watching and we’ll see you on the next blog!