Short definition
A gas water heater is a storage-tank water heater fueled by natural gas or propane. A burner under the tank heats water, and the flue rises through a tube in the center of the tank, giving up extra heat as it goes. Standard residential models run 30,000–50,000 BTU/h and recover roughly twice as fast as electric.
What it is
A standard gas tank water heater pulls combustion air at the bottom, fires a burner under the tank, and routes flue gas up a flue tube through the center of the tank to a vent at the top. That center flue acts as a heat exchanger — flue gas gives up heat to the surrounding water on its way up. From the top of the tank, flue gas exits through one of three venting types:
- Atmospheric (B-vent). Flue rises by buoyancy through a metal flue and out the roof. The legacy default.
- Power-vent. A fan pushes flue gas out a sidewall through PVC pipe. Allows installs that don’t have a roof flue path.
- Direct-vent. Sealed concentric pipe brings outside air in and pushes flue gas out a sidewall. Used in airtight homes where combustion air is limited.
Gas tank heaters typically run 30,000–50,000 BTU/h input on standard residential models, with high-recovery 65,000–80,000 BTU/h options for larger households. Recovery is about 30–40 gallons per hour at a 90°F rise — roughly twice the recovery of a standard 4,500-watt electric tank.
Why it matters to a homeowner
In WA, gas water heaters used to be the cheaper-to-run choice. With heat pump water heaters now in play and federal/utility incentives flowing toward electrification, the calculation has shifted, but gas tanks still have advantages: faster recovery, lower upfront cost, and well-understood failure modes.
The most useful things to know:
- Pilot light or electronic ignition. Pre-2010 models almost always have a standing pilot light and a thermocouple. Newer models use electronic ignition. Different diagnostic paths when the heater quits.
- Atmospheric installs need real combustion air. A heater installed in a tight closet, especially in a newer airtight home, can backdraft and trip a CO alarm. Power-vent or direct-vent fixes that.
- Sediment trap and flex connector are required at every gas appliance in WA. WA-amended IFGC requirements; inspectors check at permit.
- Seismic strapping is mandatory. Two straps, upper third and lower third of the tank, anchored to studs.
When a quote on a failed gas heater offers tankless or HPWH conversion, the math depends on your gas-line capacity (tankless often needs an upsize), your install location (HPWH wants lots of unconfined air), and your utility rebate eligibility.
When you’ll encounter this term
- A failed water heater needs replacement and you’re choosing between gas tank, tankless, electric, and HPWH.
- A pre-purchase inspection identifies an atmospheric gas heater older than 12 years.
- A CO alarm trips and the plumber traces it to backdraft at the gas heater.
- A gas-utility outage notice references “gas water heaters and furnaces” in your area.
Common variants and what gas water heater is not
- Gas tank vs. gas tankless. Tank stores hot water; tankless heats on demand. Different sizing math, different gas-line requirements.
- Atmospheric vs. power-vent vs. direct-vent. Vent style dictates closet placement, combustion air, and install cost.
- Standard vs. condensing tank. Most tank gas heaters are not condensing. Condensing tech is mostly tankless territory.
- Natural gas vs. propane. Same physical heater, different orifice. Conversion kits exist but should be installed by a licensed gas fitter.
Common failure modes
- Pilot light won’t stay lit. Thermocouple failed (older models) or flame-sensor / igniter (newer). Replace.
- Pilot lights but burner won’t fire. Gas-control valve failed.
- Yellow / lazy flame. Poor combustion air, burner clogged with dust, or vent obstruction.
- Spillage at the draft hood. Backdrafting from competing exhaust appliances. Investigate house-pressure dynamics.
- Tank leak from bottom. Anode consumed; tank rusted through. Replace.
- Sediment popping noises. Hard-water mineral buildup at the base. Flush.