The Facts About AC Condensate Drain Lines for Attic/Rooftop HVAC Systems

The Facts About AC Condensate Drain Lines for Attic/Rooftop HVAC Systems

Residential HVAC installers have to understand so many facets of the construction industry.
We’re going to talk about the importance of installing the condensate drain lines correctly so the system doesn’t cause damage to the home.
We’re not here to pretend we know or could even interpret all the codes correctly. We’re simply trying to open a conversation about the codes we cite on the job every day out there on the field without even knowing it.
But where is that code in the book? That’s what this project is all about.
Let’s take a look at what the codes say about condensate control and adherence to the code when doing an HVAC change-out.
International Mechanical Code 307.1 talks about condensate from cooling coils we are installing in people’s homes.
Condensate from air cooling coils and the overflow from evaporative coils and similar water supplied equipment shall be collected and discharged to an approved plumbing fixture or an approved disposal area.
Approved areas are at wrapped and ventilated receptor to a sanitary sewer, or a downspout that terminates to an approved area.
The most popular areas we terminate condensate drain lines are over on the side of the house and usually about six inches from the ground.

This can be in a planted area that’s large enough to accept that amount of drainage and soak down into the earth.

One area we cannot drain to is outlined in the codebooks and installation manuals of the equipment we’re installing. The places we cannot have condensate runoff drain to are 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 but what about the sidewalk on the side of the house where it may not be defined as a public walkway?

It would still be a nuisance for the homeowner and their family to have to walk through the wet spot every day in their normal activities.
We usually create a French drain using a roto hammer.

We’ll make a 3-inch hole in the sidewalk and bore through the four to six inches of concrete and we fill it up 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 then it keeps the sidewalk dry.
The inspectors say, if we discharge the condensate into the actual houses drainage system, it has to be through an indirect waste pipe. And to clarify that, an indirect waste pipe is something upstream of a trap – not downstream of the trap. This includes the main venting stack as well.

So, if we’re supposed to drain the primary into the drainage system of the house, can we terminate the drain line over a gutter and let the waterfall into the gutter? Where it will continue to the ground to an approved area?
International Mechanical Code 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 then?
If the condensate drain line includes waste from a condensing furnace, it’ll make a more acidic type of waste that needs to make it to the ground. Thin aluminum rain gutters we’re not designed to carry corrosive wastes like that down to the ground.
It’ll just rust out in a few years and create a new problem.
How 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 a schedule 40 PVC. That’s the most popular type of piping HVAC installer is used today but we can also use ABS cast iron or hard drawn copper.
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 a downward slope for every 12 inches of carrying, gravity will do all the work and pull the condensate ways to the ground all by itself.

A point we want to make to installers is that we can get caught up in this little six by four areas where we’re installing 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 drain line travels off the service platform and disappears in the insulation, that’s fine but you still need to prove to yourself that the entire drain line has at least 1/8 inch of a slope to it. We have seen some pretty big dips in PVC piping which clogs the drain line, creates a backup, and causes water damage in the house.
You’ve installed the new system and now that you’ve adapted into the existing drain line, you own that whole drain line now.
You won’t be able to say “Well, I just joined into it right there” and thought the rest of it would be okay. It’s not going to work. It’s not too much to ask for and the inspector can cite you on the fact that you may have a slope in certain sections of the drain line but if the workmanship of the installed drain line is all cattywampus the inspector can ask you to run it in a more uniform manner this time.

The idea here is to maintain straight alignment, a uniform slope, and to strap or support the drain line at proper intervals as guided by the installation manual and codebooks.
What is the proper interval to support PVC drain lines?

Every 4 feet we’re supposed to get a strap on it. Whether it’s to support the drain line with hangers or strapping 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, we cut off PVC piping to create stanchions and reinforce the downward grade off of the service platform.

This gives your drain pipe a uniform look and makes it really easy for the inspector to pass your job.
A little further up the drain line towards the evaporator coil, the question is “Do we have to install a p-trap or not?” Our inspectors are looking for a trap when it’s required by the manufacturer installation instructions.
Most of the manufacturers recommend one, they don’t require it.

“They say a field fabricated trap is not required for proper drainage due to the positive pressure of the furnace. However, it is recommended to prevent the efficiency loss of conditioned air.”
We hear the positive pressure point of view often on social media when you are talking about not needing a trap or needing a trap in the condenser line. At the very least though, a clean-out is required by code.

It says that it’s not reasonable to ask a future technician who has to come to clear a blockage to cut the PVC lines to do so. And we see far too many systems without a clean-up on them.
This mandatory clean-out allows technicians to blow out the lines with compressed air later on down the road when mold and gunk build up inside it and trust us, 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 a 3/4 inch schedule 40 PVC drain lines for all residential HVAC.

Anything over 20 tons it uses larger diameter piping. The codebook says the size of the pipe is for one or a combination of units or as recommended by the manufacturer. So, if you have two systems and you’re going to be tying to evaporator drains into one single drain line, make sure you look at the installation manual because they might want you to increase the size of the final pipe going to the outside.
One final little touch that is not code but we’d like to pass on to you is to be mindful of the lettering on the PVC piping. We always like to glue in as PVC with the letters facing away from the perspective of the person sitting on the platform.

We never stop doing it that way again because it looks clean. There’s less busyness going on in the scene with the lettering facing outwards. So, little touches like this can make the difference between a clean install and an average install.
We hope this answers some questions that you have regarding the code and HVAC installations when it comes to condensate drain lines.
If you’er installing a new rooftop HVAC system and need a quote or second opinion, call us at Red Deer Heating and AC.