Why Does My Furnace Leak When the AC Is On?

Scratching your head because the furnace is leaking water while the air conditioner is on? You’re not alone. Furnace leaks are troubling for homeowners, and our St. Louis HVAC technicians receive plenty of calls about this issue. As you might have guessed, the leaking water is condensation that has failed to drain properly.

You might try checking your drain pan and drain line to look for any blockage or tilting that you can fix yourself. We suggest calling for HVAC repairs to be safe, make sure that your furnace has not been damaged, and get everything straightened out.

Why a Furnace Leaks When the AC Is Running

Air conditioners create condensate water by necessity. While cooling down the warm supply air, any moisture in that air will condense into water as it gets cooled. The condensate drain system normally collects this water without a problem. The water evaporates or gets shooed away to a drain or the outside of the house.

The reason why a furnace leaks when the AC is running is that your furnace shares a drain line with the AC, and the drain line is clogged or has been knocked askew.

So, it appears as though the furnace is leaking, but really the excess condensation has nowhere to go. The water is spilling onto or under the furnace, and you need to fix the drain system before there’s rust or other damage to your property.

Fixing a Water Leak Around the Furnace

In most cases, the solution is not very complicated. We just need to diagnose the root of the problem and fix it. This usually involves one or more of these condensate drain problems:

  • Condensate drain line clogged with slime
  • Frozen condensate
  • Condensate drain line blocked by debris
  • Broken or cracked drain pan
  • Drain line has been knocked off balance

De-clogging can be accomplished with various methods such as compressed air or drain cleaning tablets that you can find at the hardware store. You can always call us for HVAC service in the St. Louis area if you need help with things.

You should definitely schedule HVAC maintenance if the problem has been going on for a while, or if you’re not sure how long it’s been happening. The furnace coils, burners, motor, or electrical parts may be damaged or corroded.

Get Help for AC or Furnace Leaks in St. Louis

Let us know if you need help fixing a water leak around your furnace or air conditioner. We can perform a quick inspection to find the problem and get everything cleared up. Better to call for some maintenance now rather than find out your furnace needs repairs later this year!

Metro Heating & Cooling serves Fenton, MO and the greater St. Louis area. Call us at 314-845-5900 or request an appointment online.