Gas water heater leaking from the bottom
Gas units have one cause tanks and electric heaters do not: condensation. Cold incoming water can drop the tank's outer skin below the dew point, and the moisture that forms runs down onto the burner area and the floor. It looks exactly like a leak.
If you smell gas — a rotten-egg or sulfur smell — stop. Do not touch a light switch or the heater. Leave the house and call your gas company or 911 from outside.
How to tell it's this
- Condensation: appears during a long heavy draw, in cold weather, or on a heater that was just refilled — then stops within an hour or two.
- Condensation: you may hear it sizzle on the burner. The water is clear.
- Tank failure: a steady pool that returns however long you wait, and never fully dries.
- Tank failure: rusty or discoloured water, and the unit is past about 8 years.
What to do
- Dry the floor completely and put down paper towel. Do not run hot water for two hours.
- Still bone dry? It was condensation. Nothing is broken.
- Wet again with no hot water drawn? That is a real leak, and the drain valve and T&P discharge pipe are the two things to rule out before the tank.
- If it is genuinely seeping from under the tank body, the tank has failed and the unit needs replacing.
What it costs
Condensation costs nothing to fix. A failed gas tank is a replacement: roughly $1,000–$3,000 installed depending on region, venting, and access.
Typical US ranges for 2026, not quotes. Labour is 30–50% of an installed price, so where you live moves these numbers more than anything else does. Get two or three local estimates.