What tankless actually costs to put in.
The unit price is the small half. Retrofitting an East Valley house to accept it’s the number that surprises people.
A gas tankless water heater typically runs $2,500 to $6,500 installed in the East Valley. A relatively clean retrofit sits near the bottom. The top of the range is what happens when the unit needs a larger gas line and new venting, which many tank-to-tankless conversions do. Budget separately for annual descaling: in the East Valley's scale-forming water that’s maintenance, not an extra.
Range compiled 2026-08-21 from published Phoenix-metro plumbing price guides (plumbingpriceguide.com/phoenix-plumbing-cost, phoenixplumbingauthority.com, desertrainplumbing.com, plumbingphoenixpros.com). Typical installed range for ordinary residential work, not a quote, and not a promise about your house.
Where the money actually goes
People price the unit and get a shock at the quote. The unit is often under half the job. A gas tankless heater burns considerably more gas at peak than the tank it replaces, so it frequently needs a larger-diameter gas line back to the meter, and it needs its own venting. In a 1990s or 2000s house where the tank sat in the garage on a builder-grade gas run, both of those are real work. Get the whole job quoted, not the unit. The gap between those two numbers is where the unpleasant surprise lives.
The condition attached to it
Valley water deposits scale. A tankless unit pushes water through a narrow heat exchanger, which is exactly the geometry scale punishes. Manufacturers specify periodic descaling. In water like this that instruction is load-bearing. You have three honest options: budget for it annually, fit a softener, or accept a shorter service life. Anyone selling you tankless here without mentioning that is selling, not advising.
Who it pays off for
Larger households that genuinely run out of hot water, anyone reclaiming a garage bay or closet, and homeowners staying long enough to earn back the install. It pays off least for a small household replacing a working tank on an efficiency pitch, in a house that needs a gas upgrade to accept it. That’s the case where the payback period outlives the ownership.
Almost all of the spread here is retrofit, not the appliance. The range assumes we can get gas, venting and power to where the unit is going. If the gas line has to be upsized back toward the meter, or the vent needs a new penetration, that’s added work and we’ll say so before we start. Descaling is an ongoing cost, not part of the install.
Where this page cites a utility, permit or housing figure for a specific town, it’s that town’s published data. Your own city’s water report applies to your tap and your city’s building department sets your permit rules; ask us which apply to your address.
What moves it inside the range.
Almost all of the spread is retrofit work, not the appliance.
The big one. If the existing run can’t feed the unit at peak, it gets replaced back toward the meter.
Tankless units vent differently from tanks. A new penetration and vent run is common on a conversion.
Gas tankless units still need power for controls and ignition. Sometimes there’s no circuit where the tank was.
Moving the unit from where the tank sat means new water lines as well as gas and vent.
Not part of the install price, but it decides the maintenance cost for the unit's whole life.
Answers, not a brochure.
Will it really pay for itself?
On energy alone, slowly: the savings are real but modest against an install that can be several times a tank replacement. The honest reasons to go tankless are hot water that doesn’t run out, a longer service life, and reclaimed space. If a salesperson's payback math is the main argument, ask to see the assumptions.
Do I need a softener with tankless?
Not required, and it meaningfully changes the maintenance picture. In hard water the heat exchanger will scale, and softening upstream is the alternative to descaling downstream. Either is a legitimate choice. Doing neither is the one that costs you the unit early.
Worth deciding on a day you have hot water rather than a day you don't.