Why Is My Furnace Leaking Water?

Water near a furnace most often comes from the condensate drain on a high efficiency furnace, a leaking humidifier, or, in homes where the furnace shares space with an air conditioner, the coil's drain pan. The first step is to switch the furnace off and figure out which kind of furnace you have, because that decides where to look.

A small leak is still worth taking seriously. Water near electrical components and a fuel-burning appliance can cause damage and safety concerns, and it can rot flooring over time.

Identify your furnace type

Older standard efficiency furnaces vent hot exhaust through a metal flue and produce little liquid. High efficiency furnaces pull so much heat from the exhaust that it condenses into water, which must drain away. They are usually vented through white plastic pipe, often out a side wall, and have a small drain line and sometimes a small pump.

That difference is useful. If you have a high efficiency furnace, some water production is normal, and a leak means the drainage has failed. If you have an older unit and it is leaking, the cause is more likely to be outside the furnace's own combustion system.

The usual causes

• A clogged condensate drain line or trap, often from dust and slime
• A cracked or disconnected drain hose
• A failed condensate pump that no longer moves water out
• A leaking or overflowing humidifier attached to the furnace
• A drain pan from an air conditioner coil that is full or clogged
• Poor venting or a cracked heat exchanger, which need immediate professional attention

What you can safely do

Turn the furnace off at the thermostat and, if water is near the unit, at the breaker. Then look for the source without reaching into electrical or gas components. If you have a humidifier, shut off its water supply valve and see whether the leak stops, since these are a frequent source, especially with the mineral-heavy water in our region.

Mop up standing water and keep pets and children away from the area. Check that the drain line is not visibly kinked or hanging loose. That is as far as it is sensible to go.

When to call a professional

Call a licensed technician if the leak returns after you clear it, if you suspect a cracked heat exchanger, if the furnace makes unusual noises, or if you notice a smell you cannot explain. Cleaning a clogged trap, replacing a pump or diagnosing a venting problem involves details that are easy to get wrong.

Preventing the next leak

Drains clog gradually. An annual furnace inspection includes checking the condensate system, the humidifier and the venting, so those small problems are handled before winter. Air-Tech's AT Advantage Program maintenance plans include two visits a year, which puts a heating check on the schedule each fall.

Why even a small leak matters

It is tempting to put a towel down and ignore a slow drip, but moisture has a way of spreading. Water can corrode metal parts inside the cabinet, damage the control board, stain ceilings below an attic furnace and encourage mold in a closet or crawlspace. A slow leak also tells you something has stopped working as designed, and the sooner that is fixed the smaller the repair usually is. If the furnace sits above finished space, a drain pan with a float switch is one more safeguard worth asking about. Note when the leak happens, such as only during a long run or only after a humid spell, because that detail often points straight to the cause.

If there is water around your furnace right now, call Air-Tech at (509) 392-2021. The Pasco team services all furnace brands and can send someone out day or night for emergencies.