How a Clogged HVAC Condensation Drain Can Flood Your Stockton Home


Last week we unclogged a condensation drain in Stockton. That may not sound like tantalizing stuff, but it was more than exciting for this particular homeowner. While it was a fairly cheap repair bill from us, the flooding damage that resulted in the basement was anything but a cheap fix, and the carpet repair bill was plenty exciting. The drain must have been clogged for at least a week, and every time the AC turned on (which was a lot last week), the unit sent water into the home. It soaked through the carpet and padding, stained the concrete below, and ruined two compressed wood end tables that were nearby. The carpet had to be replaced and the chairs were toast. But the client was lucky in one sense: too much longer and the AC would have been wrecked as well. Our client is not alone in this issue; in fact, it’s one of the most called-about complaints we get. So today we’re going to talk clogged drains and prevention, helping you to understand how this common problem occurs and what you can do to stop it.

How the Condensation Drain Works in Your AC Unit

As is usual when describing how something can go wrong, we start with describing how it works when all is well. Here’s an expanded version of what we told that client in Stockton, with a little more HVAC technical knowledge thrown in: 

Your AC cools air by blowing regular air over a super-cold condenser coil — this chills the air which is then blown throughout the house. Think of it like icing a drink: just as water collects on the outside of an icy drink glass, water also collects on those condenser coils as a result of the cooling process. As water condenses, it drips off the coils into a pan designed to collect the water and sends it to drain outside the home. This condensate is just a normal part of AC operation.

What’s abnormal is something clogging up the ability of the condensate to drain away. This can be the result of lots of things, but mold, mildew, or dusty sludge are the most common. When the drain becomes clogged, water will back up, first up the line and then into the drain pan. The water climbs the edges of the pan until, finally, it overflows like a runoff-filled irrigation ditch.

Problems Arise from Clogged Drains

Water damage to the carpet and other items are the most common results of overflowing condensate pans and clogged drains. Our client lost a room full of carpet as well as several tables. The floorboards in the room also got water-logged and had to be refinished. The progress of this flooding can be slow, but you’ll notice it when you feel it underfoot. Damages can really range, too —we’ve heard of structural damage caused by flooding in a summer home that wasn’t occupied for two months at a time.

Our Stockton client lucked out, though. Another common result of condensate pans overflowing is damage to the HVAC system itself and that can get costly. Like many things, your HVAC system is not designed to run when full of water. Chemicals, electricity, and components that need to stay dry (like air filters) don’t play well with overflowing drain pains. In addition, most systems use a pump of some kind or another to drain the water from the home. That pump will be pushing up against the clog in the drain, working overtime to try to get the water to go through. The resulting strain can damage the pump or other components, and when that happens it’s not easy to fix.

In newer air-conditioners, a clogged line and overflowing drain pan can actually cause the system to turn off entirely. This may sound bad, but it’s actually a good thing: many newer AC systems are designed with an overflow sensor. When the sensor is tripped by a drain pan overflowing, the system will turn off until the problem is fixed. This prevents flooding and other system damage!

The Cycle of Mold

Our friend in Stockton had been warned in the past of potential drain issues; during his last inspection we’d cleaned a lot of mold and mildew out of the system, and it came back with a vengeance to ultimately clog the line with spores. Mold and mildew are a chief cause of drain line blockages.

They’re also one of the most common results of said blockages: a pan that isn’t draining at all (or just not fast enough) can, when coupled with the condenser coils, be a great source of humid air. When the air gets humid, mold will grow. And that can mean mold grows and is then distributed all over the home because that’s what the HVAC system does. This mold can be cleaned out, but once you’ve had mold the first time, it’s much more likely to return.

We cleaned out his drain lines and inspected the system for damage. Then we went home and checked out our own drain pans and lines (it never hurts to check!). If you want to make sure your system is operating well and not about to flood your home, give us a call. It’s not worth the risk!