Replacing a water heater: what to expect, start to finish
Once you’ve been told the tank needs to go, the job itself is usually a few hours of straightforward work. The old unit gets drained and hauled off, the new one gets set and connected, and it starts heating as soon as it’s full. The exceptions are switching fuel types or moving the heater to a new spot. Those take longer and cost more, so it helps to know which kind of job you’ve got.
Picking the replacement
The simplest swap is the same fuel and roughly the same tank size as what’s coming out. Same gas connections, same electrical, same venting, same footprint. If you’re not sure what size to get, we’ve got a guide to sizing a water heater that walks through it. And if anyone’s floated the idea of going tankless while you’re at it, read tank vs. tankless first. It’s a real option, but it’s a bigger job than a straight swap, with different venting and gas or electrical needs. If you’d rather hand the whole thing off, here’s our water heater page.
What happens on install day
- Power and fuel get shut off first. Breaker off for electric, gas valve closed for gas. Nobody wants to be draining a tank that’s still heating.
- The cold water supply gets shut and the tank drains. A garden hose runs from the drain valve to a floor drain or outside. A full 40 or 50 gallon tank takes a while to empty, so this is the slow part.
- The old connections come apart. Water lines, gas line or electrical whip, the flue if it’s gas, and the T&P discharge pipe.
- The old tank comes out. On a second floor or up a flight of stairs, this is more of a project than it sounds like.
- The new tank goes in, on a drain pan where one’s called for. Pans matter most in attics, upstairs closets, or anywhere a leak could damage the floor below.
- New connections get made. Fresh flexible water connectors or copper, a new gas flex line or hardwired whip, and a new T&P discharge pipe run down to within a few inches of the floor.
- On a gas unit, the vent gets checked before it’s reconnected. A vent that suited the old heater doesn’t always suit the new one, and sometimes a section needs replacing.
- The tank gets filled completely before anything gets powered on. This isn’t optional. An electric element that powers up in a tank that isn’t full burns out fast, and heating an empty gas tank can damage it.
- Once it’s full, the burner gets lit or the breaker gets flipped, and everything gets checked for water leaks, plus gas leaks on a gas unit.
- The thermostat gets set, usually to 120 degrees, and that’s the job.
Where code changes come in
Water heater code has changed since a lot of older tanks went in, so replacing one often turns up a few upgrades:
- An expansion tank, a small tank on the cold line, if your house has a closed plumbing system (usually because of a check valve or pressure-reducing valve at the meter). Without one, the extra pressure from heating water has nowhere to go but the tank itself.
- A drain pan and discharge line, if the location calls for one and the old setup didn’t have it.
- A T&P discharge pipe that actually reaches the floor, since a lot of older installs have one that stops short or points the wrong way.
- Vent upgrades on gas units, as covered above.
The pan and discharge line keep a leak or a relief valve discharge from turning into a ceiling repair.
Check on permits. Rules vary by city. Ask whoever’s doing the work whether a permit’s needed and who’s pulling it, or call your city’s inspection office.
The first few days
Expect some air in the lines for the first day or so, which shows up as sputtering at the faucet before the water runs clean. That’s normal and clears on its own. If the hot water itself smells like rotten eggs, that’s usually the anode rod reacting with the water. Mention it if it doesn’t fade in a few days. A rotten egg smell in the air around a gas heater is a different thing. That’s gas. Leave the house and call the gas company or 911 from outside.
If a tankless switch or a move to a new spot is on the table, bring it up before install day.