Water Heater Condensation vs. Leak: How to Tell

Is It Condensation or Is My Water Heater Leaking?

Condensation on a gas water heater shows up when the tank is full of cold water and the burner is running. It drips onto the burner, may sizzle, and stops once the tank is hot. A leak keeps going no matter the tank temperature, and usually has a clear starting point on a fitting, valve or the tank.

The quick test is timing. Condensation comes and goes with heating cycles, mostly after heavy hot-water use or on cold mornings. A leak doesn't care what time it is. Water that's still showing up hours after the tank is hot, or with the burner off, is not condensation.

This page is mainly about gas tank heaters, since they're the ones that make condensation as part of normal operation. Electric tanks don't burn fuel, so water under an electric heater is almost always a leak.

Why Gas Water Heaters Make Condensation

Burning natural gas or propane makes heat, carbon dioxide and water vapor. That hot, moist exhaust rises through the flue, a metal tube that runs up through the middle of the tank. When the water around the flue is cold, the flue walls are cold too. The vapor hits them and turns back into liquid, the same way a cold glass sweats on a warm day.

That water runs down the flue and drips onto the burner. A few drops evaporate with a hiss. The rest can land in the burner area and the drain pan.

When does condensation happen most?

• First fill or first heat-up: a new heater full of cold water can drip for a few hours.
• After heavy use: long showers, laundry or filling a tub pull in a lot of cold water at once.
• Winter mornings: Apache Junction lows average about 42°F in December and January. Incoming water is colder, so the tank takes longer to warm up.
• Seasonal homes waking up: when snowbirds return in the fall and refill or reheat a tank that sat cold.

Do high-efficiency water heaters make more water?

Yes, on purpose. Condensing gas heaters pull extra heat from the exhaust, which makes a steady stream of water. They have a condensate drain line for it. If that line clogs, kinks or comes loose, water ends up on the floor. That's a drain problem, not a tank leak. Tankless units that condense work the same way, and heat pump water heaters also have a condensate drain.

Two Simple Tests to Tell Them Apart

Test 1: The dry-towel check

1. Dry everything. Wipe the tank, the pipes, the pan and the floor.
2. Wrap the likely spots. Put a dry paper towel around each fitting on top, the relief valve threads, the end of the relief pipe and the drain valve.
3. Lay a towel on the floor or pan right under the burner opening.
4. Check in 30 minutes. A wet towel on a fitting or valve is a leak. If only the towel under the burner is wet and everything above is dry, condensation is likely.

Test 2: The timing check

Note the time you see water and what the heater was doing. Then check again a couple of hours after the tank has fully heated with no one using hot water.

When It's Definitely Not Condensation

Call it a leak and act on it if you see any of these:

• Water on an electric water heater
• A wet spot that starts at a pipe fitting, nipple or flex connector
• Drips from the end of the relief valve pipe
• Water at the drain valve spout or its threads
• Wet insulation behind the burner or element access panel
• Rust streaks running down the outside of the tank
• Water still collecting hours after the tank is hot
• A puddle that gets bigger each day instead of drying out
• Water coming out from under the outer jacket at the bottom seam

For a top-down check of every leak spot, use our water heater leak finder. If the water starts on the connections above the tank, our page on a water heater leaking from the top goes through each one. If it seems to come from the base, see leaking from the bottom.

When Condensation Is a Warning Sign

Some condensation is normal. A lot of it, all the time, is telling you something.

Can a water heater be too small for the house?

Yes. If a tank is undersized for the people using it, it's always refilling with cold water and the burner runs almost nonstop. The tank never gets fully hot, so condensation never stops. Running out of hot water often, plus water at the burner most days, is a sign. A thermostat set very low can do something similar. The Department of Energy suggests about 120°F for most homes.

Could a venting problem cause condensation?

It can. A blocked, damaged or poorly sloped vent keeps moist exhaust in the flue longer, so more of it condenses and runs back down. Worse, poor venting can spill exhaust into your home. Rust or water stains at the draft hood on top of the tank, soot or scorch marks around the burner opening, or a flame that looks lazy and yellow are all reasons to stop and call.

Can condensation damage a water heater?

Short bursts don't. Constant dripping over months can rust the burner, the burner tray and the bottom of the tank, and can put out a pilot light. In a mobile-home closet or on a wood garage platform, the water also soaks into the floor or stand. So even if it's "only" condensation, constant water is worth fixing.

What to Do Next

If your tests say condensation and it only happens on cold mornings or after big hot-water use, keep an eye on it and keep the pan and its drain line clear. If the tests point to a leak, shut off the cold water and set the gas to "Pilot" or turn off the breaker. Our shutoff guide shows the steps.

Brand-new heaters often drip a bit on their first heat-up. If yours is still dripping after a day, see our page on a new water heater leaking. Apache Junction Water Heater Pros is open 24/7 for water heater leak repair in Apache Junction, and we'll tell you honestly if what you're seeing is normal.

Condensation vs. Leak FAQs