Water Dripping at a Water Heater's Vent Collar
On this page (5 sections)
The Short Answer: On a gas tank, the vent collar is where the draft hood (or a power-vent blower) sits over the flue on top of the heater. Water there usually comes from condensation in the flue or vent, rain entering the vent cap, or a water fitting on top of the tank. Less often, the flue tube inside the tank has corroded through. Repeated wetness with soot or a yellow flame is a venting problem that needs prompt service.
What the wetness looks like, and what it usually means
| What you see | Likely source | Urgency |
|---|---|---|
| A few drops around the collar shortly after the burner starts on a cold tank, gone once it is hot | Flue condensation | Normal in moderation |
| Drips only after rain or snow | Rain entering the vent cap or roof flashing | Have the cap and flashing checked |
| Steady dripping every time the heater runs, rust on the vent pipe or hood | Vent condensing too much: long or oversized run, cold space, or poor draft | Service soon |
| Water running to the collar from the relief valve or the hot and cold connections | Fitting leak on top of the tank | Repair the fitting |
| Rust flakes or water inside the flue opening with all fittings dry | Corroded flue tube inside the tank | Replace the heater |
| Soot, scorch marks, or a yellow flame along with the water | Poor draft or spillage | Turn the heater off and call now |
A. O. Smith’s condensation bulletin (opens in a new tab) explains why a cold tank produces condensation that can look like a leak, and why it fades as the water heats.
Why venting matters here
A standard atmospheric gas heater depends on warm flue gases rising up the vent. If the vent is too long, too large, runs through a cold attic, or has a poor slope, the gases cool and their water vapor condenses inside the pipe. That water runs back down to the hood. Chronic condensation rusts the vent and hood, and the same conditions that cause it can also allow exhaust to spill into the room. That is why steady dripping at the collar deserves a venting inspection rather than just a towel. Water heater vent pipe leaking covers leaks along the pipe itself.
Power-vent heaters use a blower and a plastic or metal vent; water at the blower outlet usually means the vent is not sloped as the installation manual requires or condensate is collecting in the run.
What you can check safely
- Note when the water appears: on a cold start, after rain, or every time the burner runs.
- Look at the relief valve and the hot and cold connections on top of the tank for dampness that could be running to the collar.
- Look at the draft hood and the vent pipe above it for rust, soot, or a joint that has separated. Do not tape or seal anything.
- From outdoors, look at the vent cap for damage, debris, or a missing cap.
- Confirm you have working carbon monoxide alarms near sleeping areas and on the heater’s level.
What the technician will check
A gas technician tests the draft at the hood while the burner runs, checks for spillage and carbon monoxide, and inspects the vent size, length, slope, and connections against the heater’s installation instructions and local code. They look down the flue for rust and scale that would indicate the tank’s flue tube is failing. Venting repairs range from resealing or replacing a section of pipe or a cap to rerouting or lining the vent. A failed flue tube means replacing the heater.
Frequently Asked Questions
Q: Is some water at the draft hood normal? A: A little condensation for a few minutes after the burner starts on cold water is common, especially in winter. Water that appears every cycle, keeps dripping once the tank is hot, or leaves rust and soot is not.
Q: Can I seal the collar with foil tape or silicone? A: No. Sealing the hood or collar does not stop the water source and can interfere with how the draft hood is designed to work. Have the vent inspected instead.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- A. O. Smith technical bulletin 15: condensation (opens in a new tab)Why combustion condensate can resemble a tank leak; not a diagnosis of another manufacturer’s model.
- CPSC: carbon monoxide fact sheet (opens in a new tab)Carbon monoxide hazards and emergency response.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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