Furnace Leaking Water in Las Vegas: Where the Water Is Coming From

A furnace that burns gas should not leave a puddle, but that does not mean the water comes from the burners. In Las Vegas homes the water usually comes from one of two places: the furnace's own condensate (on high-efficiency models) or the air-conditioning coil that sits on top of the furnace.

Colton Air Conditioning schedules these calls Monday–Friday, 8am–5pm.

This page is about water at the furnace during heating season. For water from the indoor unit while the AC is running, see AC leaking water.

First: safety

• If water is near electrical connections, turn the furnace off at its switch or breaker if you can reach it without standing in water.
• If you smell gas or a CO alarm sounds, leave the house and call 911 from outside.

Source 1: condensate from a high-efficiency furnace

High-efficiency gas furnaces pull so much heat out of the exhaust that water condenses inside the furnace. That water is supposed to drain through tubing, often with a small trap, to a floor drain or a condensate pump.

Signs this is the source:

• Water only appears when the heat is running
• The furnace vents through plastic pipe, not a metal flue
• Water near the drain tubing, trap, or condensate pump

Common causes: a clogged trap or drain line, a cracked or disconnected tube, or a condensate pump that stopped pumping. A furnace with a metal flue usually does not make condensate in normal operation, so water there points to another source.

Source 2: the AC coil drain above the furnace

In most split systems, the AC's indoor coil sits directly on top of the furnace, and both share the blower. That coil has its own drain pan and line.

Signs this is the source:

• Water showed up after the AC ran recently, or on a warm October afternoon when the cooling came on
• Water runs down the outside of the furnace cabinet from above
• Rust or water stains on top of the furnace

A clogged coil drain or a rusted pan can drip onto or into the furnace. Over time that water can rust parts and wet the filter, which is one reason people search "furnace filter wet."

Other possibilities

• A humidifier attached to the furnace, if your home has one
• A water heater in the same closet. Check that it is not the one leaking

Safe home checks

1. Note when the water appears: heat running, AC running, or both.
2. Look at the vent pipe: plastic or metal.
3. Check the filter. Replace it if it is wet.
4. Look for a condensate pump and whether it is full or quiet.
5. Wipe the area dry and watch where new water starts.

Do not open the furnace's sealed compartments or take apart gas parts.

When to call

Call when water keeps coming back after you dry it, water reaches wiring or the control board, the filter keeps getting wet, or a condensate pump has stopped.

Have ready if you can: when the water shows up, plastic or metal vent pipe, and a photo of where it pools.

Hours are Monday–Friday, 8am–5pm.

FAQ

Is it normal for a furnace to make water?

High-efficiency furnaces make condensate by design. It should go down the drain, not onto the floor.

Why is my furnace leaking water only when the heat is on?

That usually points to the furnace's own condensate drain, trap, or pump on a high-efficiency model.

Why is my furnace filter wet?

Often the AC coil above the furnace or a condensate line is dripping where it should not. Replace the filter and find the source.

Is this the same as an AC leak?

Not always. The AC coil drain can leak onto the furnace, but furnace condensate is a separate drain. See AC leaking water for cooling-season leaks.

What hours can I reach Colton?

Monday through Friday, 8am to 5pm.

Water at the furnace that keeps coming back? Call Colton Air Conditioning at (702) 738-6976 Monday–Friday, 8am–5pm. Tell us when it leaks and what the vent pipe looks like.

Colton Air Conditioning · Las Vegas Valley residential HVAC · Monday–Friday 8am–5pm

Call (702) 738-6976 or Book Online. License 0092120. Hours Monday through Friday, 8am to 5pm. Saturday and Sunday are closed.

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