How do I flush my condensate drain line?

Flushing your condensate drain line is a straightforward maintenance task that most homeowners can handle safely — it's one of the few HVAC maintenance jobs that doesn't involve gas or refrigerant.

What the condensate drain does is remove the moisture your air conditioner or high-efficiency furnace pulls from the air during operation. Over time, algae, mold, and debris build up inside the drain line, causing clogs that can lead to water damage, system shutdowns, or basement flooding.

What you'll need: white distilled vinegar (or a condensate drain cleaner tablet), a wet/dry shop vac, and a funnel. Turn your system off at the thermostat before you start.

Finding the drain line is your first step. Look for a white PVC pipe (usually ¾" diameter) near your indoor air handler or furnace. It will run to a floor drain, utility sink, or outside. There's typically a T-shaped access port with a cap on it — that's where you'll pour your cleaning solution.

To flush the line, remove the cap from the access port and slowly pour about 250ml (one cup) of undiluted white vinegar into the opening. Let it sit for 30 minutes to break down any algae or buildup. Then flush with warm water. If you have a shop vac, you can also attach it to the outdoor end of the drain line and suck out any blockage — this works very well for stubborn clogs.

Do this every 1-3 months during cooling season. If your system has a float switch (a safety shutoff that triggers when the drain backs up), you may notice your AC stopping unexpectedly — a clogged condensate line is often the culprit.

When to call a pro: If you're seeing water pooling around your air handler, notice musty odors coming from your vents, or the line keeps clogging despite regular flushing, it's worth having a technician inspect the drain pan and evaporator coil for mold or damage. This can be bundled into an annual AC tune-up, which runs $150–$200 in Ottawa.

For a full system inspection or to book a maintenance visit, feel free to reach out to Ottawa HVAC Pro — keeping your drain line clear is a small task that prevents expensive water damage down the road.