Water Heater Replacement: What the Job Involves
A standard water heater replacement takes a plumber 2 to 6 hours and costs $600 to $3,100 installed, according to HomeGuide's 2026 figures. The swap itself is simple; what stretches the day and the bill is draining and hauling the old tank, then bringing the new one up to the code your town enforces today.
Repair or replace?
A.O. Smith puts the average life of a water heater at about 8 to 12 years, depending on water quality, installation and maintenance. A tank past 10 years old that leaks around the base or runs erratically is a replacement candidate, not a repair. HomeGuide uses a similar rule of thumb: replace a unit over 10 years old, or when the repair would cost more than half the price of a new one.
A leak from the bottom of the tank settles it. HomeGuide notes that water leaking from the bottom usually means the tank itself is damaged, and a rusted-through tank can't be patched.
Before you shop, read the nameplate on the side of the old heater. It lists the tank capacity and the model and serial numbers. Matching the size and fuel type is the cheapest path. While you're down there, look at the route out of the house: tanks that went in before a basement was finished don't always leave through the same door.
What happens on replacement day
Here is the order a plumber works in, based on A.O. Smith's installation guide. Your installer may shuffle a step, but the pieces don't change.
Kill the energy
Gas: close the supply valve to the heater. Electric: switch off the breaker and confirm with a noncontact tester.
Cool the water down
Run a hot tap until the water turns cool, which takes about 10 minutes or more. This keeps the drain water from scalding anyone.
Shut the cold supply and drain the tank
A hose goes on the drain valve and runs to a floor drain or outside. If heavy sediment stops the tank from draining fully, that can turn into a slow job.
Disconnect everything
Water lines, the T&P discharge pipe (the pipe running down from the temperature and pressure relief valve), and either the gas line or the wiring. On a gas unit, the vent pipe comes off the draft hood once it's cool.
Haul it out
Tanks are heavy, so have a second person there to help. HomeGuide prices removal and disposal at $75 to $500.
Set the new heater
A gas unit goes into a drain pan. The water connections get heat trap fittings and 3/4-inch NPT adapters.
Fit a new relief valve and discharge pipe
Never reuse the old T&P valve. The discharge pipe should have a 3/4-inch inside diameter, slope downward, and end 1 to 6 inches from a drain or outside.
Reconnect gas or power
Gas joints get checked with soapy water or bubble solution; bubbles mean a leak. Electric units get the ground wire attached securely.
Fill before you fire
Open the cold supply and a hot tap and let it run until the flow is steady with no air. A.O. Smith says to let it run for 3 minutes to purge the air. Never turn on an empty electric heater, because that can damage the heating elements.
Light or power up and set the temperature
A.O. Smith recommends 120°F. Expect the first tank to take 1 to 2 hours to heat.
Then comes the inspection, if your town requires one.
Code upgrades that often come with it
This is where quotes differ most. An old heater may have been legal when it went in and still fail inspection as a new install.
- Expansion tank. If your plumbing is a closed system (a check valve or pressure-reducing valve at the meter), A.O. Smith calls for a properly sized and charged expansion tank. This is the small "pressure tank" people mean when they search for a water heater pressure tank replacement. HomeGuide puts installation at $100 to $400.
- Drain pan. A.O. Smith specifies a metal pan at least 2 inches wider in diameter than the heater and no deeper than 1.75 inches.
- Venting. Replacing existing vents runs $100 to $600, and venting a location for the first time runs $500 to $1,500.
- Gas line or circuit. A bigger gas supply line costs $350 to $2,000, and a new dedicated electrical circuit costs $250 to $900.
- Earthquake straps. Some regions require the tank to be strapped to the wall. Your building department will tell you if yours does.
What it costs
HomeGuide's 2026 numbers for the common line items:
| Item | Typical cost |
|---|---|
| Standard tank, installed | $600 to $3,100 |
| Labor only, standard tank | $200 to $1,000 |
| Removal and disposal | $75 to $500 |
| Permit (gas or electrical work) | $50 to $200 |
| Expansion tank, installed | $100 to $400 |
For a full breakdown by tank size and fuel, see water heater replacement cost.
Switching to tankless or heat pump
Changing the type of heater turns a swap into a small remodel. HomeGuide puts the labor alone for a tank-to-tankless upgrade at $600 to $2,500, and a gas tankless unit often needs a bigger gas line and new venting. Our tankless water heater installation page covers what changes. Heat pump models need room to breathe: A.O. Smith calls for at least 450 cubic feet of air space. See heat pump water heater installation.
Mistakes to avoid
- Reusing the old T&P valve. It's a safety device, and the new heater ships with its own.
- Turning on an electric heater before it's full. A.O. Smith warns this can damage the heating elements.
- Skipping the leak test on gas joints. Soap and water costs nothing.
- Upsizing without checking supply. A bigger tank or higher-input burner may need more gas or amperage than the house provides.
- Forcing a clogged drain valve. If sediment keeps the tank from draining, get professional help.
Low hot water pressure after replacement
This is a common complaint right after a swap. Start simple: make sure the cold supply valve above the heater is all the way open. Then pull and rinse the faucet aerators, because sediment stirred up during the job tends to end up there. If only the hot side is weak at every fixture, ask the installer to check the new fittings at the top of the tank.
Power-vent, RV and camper units
A power-vent gas heater has a blower and a pressure switch that proves the exhaust is moving before the burner lights. A failed pressure switch on an otherwise healthy unit is a repair, not a reason to replace the heater. RV and camper tanks are a different product with their own sizes and fittings. For those, start with RV water heater repair.
DIY or hire it out
A handy owner can swap an electric tank where the circuit, pan and discharge pipe are already right. Gas work, venting changes and anything that needs a permit belong to a licensed plumber. A mistake on the flue can push carbon monoxide into the house, and that's not a risk worth a few hundred dollars.
FAQ
How much does it cost to replace a water heater?
HomeGuide's 2026 range for a standard tank is $600 to $3,100 installed. Labor alone usually runs $200 to $1,000. Code upgrades, venting and a fuel change push it higher.
How long does it take to replace a water heater?
A tank replacement takes 2 to 6 hours, and a new tankless install can take up to 10 hours. Add 1 to 2 hours for the new tank to heat its first load.
When should you replace a water heater?
Plan for it once the heater passes 10 years, or sooner if it leaks from the tank or behaves erratically. A.O. Smith's average range is 8 to 12 years. See how long water heaters last.
Can I replace my tank water heater with a tankless one?
Yes, but budget for more than the unit. Gas models often need a larger gas line and new venting, and electric models may need new circuits. HomeGuide puts the labor alone at $600 to $2,500.
Do I need a permit to replace a water heater?
In many towns, yes, and an inspection may follow. Check with your local building department before the work starts.
Sources
- HomeGuideWater Heater Installation Cost (opens in a new tab)
- A. O. SmithWater Heater Installation Guide (opens in a new tab)
- A. O. SmithWater Heater Repair or Replace? (opens in a new tab)
- HomeGuideWater Heater Repair Cost (opens in a new tab)
- HomeGuideTankless Water Heater Installation Cost (opens in a new tab)