Water heater replacement, decided before it fails

What is water heater replacement?

Replacing a water heater is two decisions, not one. First, what type replaces it - a storage tank on the same fuel, a tankless unit, or a heat pump water heater - which is decided by your fuel supply, the space, and how your household actually draws hot water. Second, what the replacement drags along with it: a permit, an expansion tank, updated venting or a modern relief-valve discharge, because a replacement is inspected against today's code and not the code your old unit was installed under. Getting the first decision right is worth more than shopping the second.

Signs you need water heater replacement

• Rusty or metallic-tasting hot water that runs clear on the cold side - the tank lining is failing, and lining failure is terminal
• Water pooling under the tank rather than dripping from a fitting above it
• You are running out of hot water noticeably sooner than you used to, with no change in household size
• The unit is old enough that you cannot find the data plate, or the installer sticker is from a company that no longer exists
• A rumbling or popping noise on every heating cycle that a flush no longer quiets - hardened sediment sitting on the burner surface
• You have already paid for one repair this year and a second part has now failed
• You are remodelling, converting a garage, or adding a bathroom, and the existing unit was already at its limit
• You are selling, and an unpermitted or visibly corroded heater is going to come up in the inspection report anyway

Seeing something not on this list? Browse water heater problems by symptom →

How water heater replacement actually works

1. 1

   Decide the type before you shop the unit

   The four realistic routes are a gas storage tank, an electric storage tank, a tankless unit, or a heat pump water heater. What decides it is not efficiency marketing - it is what fuel reaches the space, how much air and headroom the space has, whether there is a drain nearby, and how long you plan to stay in the house. Each route has a dedicated page here that will talk you out of it if it does not fit.

   Watch forBeing routed to a type because it is what the installer stocks. Ask directly: "which of the four did you rule out for my house, and why?" An installer who has considered and rejected the other three is giving you a decision. One who only ever proposes one is giving you their inventory.

2. 2

   Size it to how your household actually draws hot water

   Storage tanks are sized by first hour rating - how much hot water the unit can deliver in the busiest hour, which combines stored volume with how fast it reheats. Tankless units are sized instead by flow rate at your required temperature rise, because they never store anything and must heat water as it passes. These are different units of measurement answering different questions, and a tank capacity figure tells you nothing useful about a tankless unit.

   Watch forSizing by "same as what you had". The old unit may have been undersized for years and everybody adapted around it, or oversized because a previous owner had a larger family. Describe your actual worst-case hour - the morning where showers, the dishwasher and the laundry overlap - and let the installer work back from that.

3. 3

   Site survey: space, clearances, drainage and access

   Somebody should look at where the unit lives before quoting. Attic and upper-floor installations need a plumbed drain pan because a failure there does not stay there. Garage installs have their own restrictions in many jurisdictions. Tight interior closets rule some types out entirely. And the old unit has to physically get out - narrow basement stairs and tight mechanical rooms genuinely change what can be installed.

   Watch forA quote given entirely over the phone from a model number. It will be re-quoted on install day, and the second number is the one you pay.

4. 4

   Permit and the code items it triggers

   In most US jurisdictions water heater replacement is permitted, inspected work. The permit is what forces the items your old installation may not have: thermal expansion control, a correctly terminated relief valve discharge, seismic restraint in some regions, drain pans, and compliant venting or combustion air. Requirements vary by city and state - the local building department is the authority, not a national blog.

   Watch forA cash discount for skipping the permit. It shifts every code liability onto you, voids some manufacturer warranties, and reliably surfaces during a home sale. It is also the single clearest signal about how the rest of the job will be done.

5. 5

   Shut down, drain and remove the old unit

   The fuel or power is isolated and the old unit is drained down before it moves - a full storage tank is far too heavy to handle safely, and draining a tank full of hardened sediment can take much longer than expected. Connections are cut back to a clean point rather than reused blindly.

   Watch forOld shut-off valves and supply connections being reused because they still look fine. A valve that has not been turned in a decade often will not seal again once it has been moved, and the time to find that out is while the installer is still standing there.

6. 6

   Set, connect and bring the installation up to current code

   The new unit is set level, connected to water, connected to its fuel or circuit, vented if it needs venting, fitted with any required expansion tank and pan, and given a relief valve discharge that terminates where a discharge is allowed to terminate. This is also the point where a fuel or type change ripples outward, because a different unit style rarely reuses the previous vent, circuit or gas run unchanged.

   Watch forA relief valve discharge that ends somewhere convenient rather than somewhere compliant - pointed at the ceiling, threaded down to a reduced size, or terminated inside a closed cabinet. It is a safety device, and it is the most commonly botched item on an otherwise tidy install.

7. 7

   Fill, purge, test and set the temperature

   The unit is filled with the air purged from the lines before any heat is applied, then fired or energised, checked for leaks at every joint, and set to a delivery temperature. On gas units the combustion and draft get verified. You should be shown the shut-off, the relief valve, and how to isolate the unit in a hurry.

   Watch forBeing handed a running unit with no walkthrough. Knowing where your water and fuel shut-offs are is worth more, on the day something goes wrong, than any feature on the unit.

8. 8

   Disposal, permit close-out and warranty registration

   Haul-away of the old unit is normally included but is worth confirming in writing, since a drained tank left in a garage becomes your problem. The permit needs to be signed off by the inspector, not merely pulled. And most manufacturers require registration within a set window, plus proof of professional installation, before the warranty is worth anything.

   Watch forA permit that was pulled but never closed. Ask for the final inspection sign-off, not the permit number - an open permit is a live issue at resale.

What does water heater replacement cost?

Most replacements land roughly between $1,500 and $6,000 installed, with heat pump and tankless retrofits typically at the upper end. The gap between two quotes is usually the code items - permit, expansion tank, venting, electrical - rather than the appliance. See the cost guide for a full breakdown.

See the full water heater replacement cost guide - by material, size and region →

If the number is the problem, here are the ways people pay for it →