Tankless vs. Tank: Running the Numbers on a Ten-Year Hold

A storage water heater spends its life solving a problem you do not have yet: it keeps forty or fifty gallons hot around the clock in case somebody wants a shower. The energy spent maintaining that readiness — standby loss — is money burned against a future maybe.

A tankless unit refuses the premise. It heats water when a tap opens and stops when it closes. No tank, no standby loss, no running out on the fourth shower. On paper it is simply the better machine. The brochure stops there. The spreadsheet does not.

The honest ledger

Install cost. A straight tank swap in the Valley runs roughly $1,400–$2,200. A tankless conversion runs $2,800–$3,800, because it is not a swap — it usually wants a larger gas line, different venting, and a wall that was not designed for it.

Running cost. A standard tank operates around 0.60 efficiency; a condensing tankless around 0.90. For a typical family that difference is worth roughly $80–$180 a year at current gas rates. Real money, but patient money.

Lifespan. Here the tankless earns its keep: about twenty years against a tank’s eight to twelve in our hard water — provided it is descaled annually, which costs about $120 or a Saturday morning. Skip that maintenance in Phoenix water and the twenty-year machine becomes a ten-year machine with a premium purchase price.

When each one wins

• Staying ten-plus years, decent hot-water usage, gas already adequate: tankless usually pays back between years eight and fifteen and then runs another decade in profit. Endless showers are a bonus the spreadsheet doesn’t price.
• Selling within five years: keep the tank. You will donate the payback period to the next owner, and Phoenix buyers do not pay a premium for water heaters.
• Low usage — a one- or two-person household: the standby loss you would eliminate is small. The arithmetic rarely closes.
• Electric-only homes: electric tankless wants alarming amperage. Heat-pump water heaters are the better upgrade, and a different article.

Buy the machine your next ten years needs, not the one the brochure photographs best.

The part nobody prints

Whatever you choose is being installed into 15-plus-grain water. A tank without treatment dies young; a tankless without descaling chokes. The water treatment decision and the water heater decision are the same decision, made once or paid for twice.

Our tankless savings calculator runs your household size, gas rate and ownership horizon rather than a national average — and it will tell you to keep the tank when that is the answer. If the numbers close, we install both kinds, permit included, sized to your actual draw.

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