Why Is My Furnace Leaking Water When the Heat Is On?

Is It Normal for a Furnace to Produce Water?

It depends on your furnace type. High-efficiency condensing furnaces (90 percent AFUE or higher) produce water as a normal part of operation. Standard-efficiency furnaces should not.

High-Efficiency Furnaces and Condensation

Condensing furnaces extract so much heat from combustion gases that the exhaust cools below the dew point, producing condensate. This water drains through a condensate line to a floor drain or pump.

Common Causes of Furnace Water Leaks

1. Clogged Condensate Drain Line

Algae, sediment, or debris can block the drain line. Clear it by flushing with water and white vinegar.

2. Cracked or Disconnected Drain Tubing

Plastic tubing that carries condensate can crack in cold utility rooms.

3. Failed Condensate Pump

If your furnace uses a condensate pump, it may have failed.

4. Humidifier Leak

A whole-house humidifier attached to your furnace could be the water source.

5. Heat Exchanger Issue

In rare cases, a secondary heat exchanger problem can cause water to leak.

What to Do

1. Identify your furnace type (check the AFUE rating)
2. Inspect the condensate drain line and tubing
3. Check the condensate pump if applicable
4. Look for humidifier-related leaks
5. Call a professional if the source is unclear

JT Plumbing Heating & Air serves Fort Collins, Loveland, Windsor, Greeley, Wellington, Berthoud, Longmont, Johnstown, Eaton, Evans, and Mead. Contact us or call (970) 818-1613 for service.