Tankless vs Tank Water Heater Calculator
Example: Tank heater annual energy cost: 500 $ · Efficiency gain from tankless: 25 % · Extra upfront cost of tankless: 1500 $
| Payback period | 12 |
| Annual energy savings | $125 |
| Tankless annual cost | $375 |
Worked example
If your tank water heater costs $500 a year to run and a tankless unit is 25% more efficient, the tankless costs about $375 a year, saving $125. If the tankless system costs $1,500 more to buy and install, the extra cost pays back in about 12 years. Tankless units also last longer — often 20 years versus 10 to 12 for a tank — so they can still come out ahead over their full life even with a slow energy payback.
Frequently asked questions
How much does a tankless water heater really save?
The Department of Energy estimates tankless units are typically 8 to 34% more efficient than tanks, with the largest gains for low-hot-water households, since they eliminate standby losses. Enter an efficiency gain in that range based on your usage; heavy users see smaller percentage gains than light users.
Why is the payback often long?
Because water heating is a modest share of most energy bills, the yearly savings are limited, while tankless units cost more to buy and install. The upgrade makes the most sense when your old tank is failing anyway, or when you value endless hot water and the space savings alongside the energy reduction.
Do tankless heaters last longer?
Yes. Tankless units are commonly rated for around 20 years, roughly double a conventional tank's 10 to 12 years. Over that longer life the energy savings compound and you avoid one replacement, which improves the total economics beyond the simple payback shown here.
Are there rebates for high-efficiency water heaters?
Federal tax credits and many utility rebates apply to qualifying high-efficiency and heat-pump water heaters. Subtracting those from the price difference you enter shortens the payback, sometimes substantially, so check what is available before deciding.