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Tank vs. tankless, over ten years, with the math shown.
Every tankless sales page quotes the fuel savings. Few quote the $120-a-year descale that Valley hard water demands, or the replacement tank you will buy either way. This calculator counts all of it. For some households the honest answer is keep the tank — and when it is, it says so.
Valley hard water retires most tanks around year ten.
Phoenix-metro residential gas runs about $1.40/therm.
Stay with a tank — 10-year cost
$4,228
$243/yr in fuel, plus the replacement tank you buy when this one dies.
Switch to tankless — 10-year cost
$6,119
$162/yr in gas, plus $120/yr descaling.
10-year extra cost of tankless
$1,891
Payback point
None within 20 years
Keep the tank.
At your usage, the fuel savings do not cover the annual descale, let alone the $1,500 up-front gap. A $1,800 tank is the economic answer here, and it is not close — you would be roughly $1,891 worse off over ten years. Buy tankless for endless showers if you want them. Just do not buy it for the math.
The assumptions
- Tank: $1,400–$2,200 installed (we use the $1,800 midpoint), ~0.60 UEF for gas, ~0.92 for electric, and a ~10-year working life in Valley hard water.
- Tankless: $2,800–$3,800 installed (midpoint $3,300), ~0.90 UEF gas condensing, ~20-year life with an annual descale at about $120.
- Hot water demand: 17 gallons per person per day at typical usage, heated through a ~67°F rise. Light and heavy usage scale that by 0.7× and 1.3×.
- If your current heater is electric, the tankless option is still modelled as gas — that is what gets installed here. If your home has no gas line, add the cost of running one before trusting the payback figure.
- Fuel prices are held flat for ten years. They will not be, but guessing the direction is astrology, not arithmetic.
Either way the math falls, we install both. See tankless installation or standard water heaters for flat pricing.
How to read this number
The ten-year figure is the one that matters. Tankless wins or loses on the gap between a lower fuel bill and a higher install cost, and ten years is long enough for that gap to settle. If the savings line is positive and the payback lands inside seven years, the switch is a real investment, not a comfort purchase. The unit will still have a decade of life left when the tank would be on its second replacement.
If the number is negative, believe it. Electric households see this most: the fuel arithmetic assumes a gas tankless, and if the house has no gas line, trenching one in eats the payback whole. A close result is a genuine tie — decide on endless hot water, not on money, because the money is a wash.
What the model cannot see is your actual water heater. A twelve-year-old tank in Phoenix is living on borrowed time, and replacement timing changes the math more than any rate input. When yours fails, you will make this decision in an afternoon. Better to make it now, with the assumptions visible and nobody standing in your garage waiting for a yes.
Run the real numbers on your house.
We size and quote both tank and tankless, flat price up front. If the tank is the better buy for your usage, that is what we will tell you.
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