Water Heater Exhaust Blower Noise: Causes
On this page (6 sections)
The Short Answer: A power-vent water heater’s blower pushes exhaust outdoors. A steady whoosh while the burner runs, and briefly after, is normal. A new squeal or grind usually means worn bearings or a fan wheel rubbing its housing. Gurgling suggests water in the blower or vent, and a rattle suggests something loose or debris in the fan. Replace a failing blower before it stops.
What the sound tells you
| Sound | Likely cause | How soon to act |
|---|---|---|
| Smooth whoosh during heating, stops shortly after the burner | Normal operation | None |
| High squeal or chirp, getting worse over weeks | Motor bearings wearing | Schedule service soon |
| Grinding or scraping | Fan wheel rubbing the housing, or a failing bearing | Service soon; turn the heater off if it is getting louder |
| Rattle or tick | Loose mounting screws, cover, or vent connection, or debris in the fan | Service; check the outdoor termination |
| Gurgling or sloshing | Condensate collecting in the vent or blower housing | Service; vent slope or drain needs correcting |
| Hum without the fan turning | Motor or capacitor failure | Turn off; see blower not working |
| Fan keeps running after the burner stops for a long time | Control or switch issue | See water heater fan keeps running |
| Bang at the moment the burner lights | Delayed ignition, not the blower | Turn off; see water heater made a loud bang |
Why it matters
The burner relies on the blower to move exhaust, including carbon monoxide, outdoors. A pressure switch confirms the blower is working before the burner lights. As a blower fails, it may slow down, trip the pressure switch, and cause the heater to shut off partway through a cycle (see water heater shuts off after 5 minutes). Eventually it stops altogether. A failing blower is a part to replace. It should never be bypassed so the burner can keep firing.
Water in the blower or vent
Power-vent exhaust is warm and moist, and some condensation in the vent is expected. The vent is supposed to be sloped so that water drains away, either back toward the heater’s drain point or to the outdoors, depending on the manufacturer’s instructions. If the vent sags, or the condensate drain is blocked, water pools and you hear gurgling, and over time it can corrode the blower. Water dripping from the outdoor termination is covered in water dripping from the water heater exhaust.
What you can check safely
- Listen for when the sound happens: at startup only, throughout the burn, or after shutdown.
- From the ground outside, look at the vent termination for nests, leaves, ice, or a damaged cap.
- Look for water or rust stains around the blower and along the vent pipe.
- Don’t oil the motor unless the manual shows oil ports. Most blower motors on these heaters are sealed.
- Don’t remove the blower cover or disconnect the pressure switch tubing.
What the technician will check
A technician will isolate power, inspect the blower wheel and motor bearings, and check the housing and mounting. They examine the vent’s slope, joints, and condensate drainage, and confirm the pressure switch and tubing are dry and working. Blower assemblies are usually replaced as a unit, and after replacement they confirm the heater vents and fires correctly. On an older heater, they may compare the repair cost with replacement.
Frequently Asked Questions
Q: Is a noisy blower dangerous? A: The noise itself is not, but it signals a part that is wearing out. The risk comes when the blower slows or stops, which is why the heater has a pressure switch. Never bypass that switch. Replace the blower if it is failing.
Q: Does an ordinary gas water heater have an exhaust blower? A: No. Standard atmospheric tanks vent by natural draft through a metal flue and have no blower. If your heater has no fan on top, the noise is coming from something else; see the water heater noises hub.
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.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
- CPSC: carbon monoxide fact sheet (opens in a new tab)Carbon monoxide hazards and emergency response.
Editorial standards and corrections · Prepare a useful service request