Tankless Water Heater Savings Calculator
Compare annual water-heating energy cost with a tankless scenario and the incremental installed cost versus the replacement you would otherwise buy. Fuel, sizing and installation determine the real result.
Quick answerIf water heating currently costs $600/year and a tankless option reduces that energy cost by 15%, the modeled saving is $90/year and the new annual cost is $510. A $1,500 net incremental upgrade has a simple payback of 16.7 years and remains $600 behind after 10 unchanged years.
Change any number below — your result updates instantly, no button to click.
Your details
Results
Net incremental cost divided by modeled annual saving.
Ten unchanged years of energy savings minus net incremental cost.
Compare equipment only after temperature-rise and infrastructure checks
Required flow at the design temperature rise, fuel or electrical capacity, venting, condensate, water quality, clearances and qualified installation matter more than headline GPM.
As an Amazon Associate we earn from qualifying purchases. We may earn a commission from links on this page, at no extra cost to you.
Amazon opens in a new tab. A listing is not a sizing or installation plan. Confirm fuel, design temperature rise, simultaneous flow, gas or electrical capacity, venting, condensate, water quality, clearances, permits, warranty conditions and qualified installation before ordering.
How it works
Annual saving = current annual water-heating energy cost × modeled reduction percentage. Estimated new annual energy cost = current cost − annual saving. Net upgrade cost = incremental installed cost − confirmed rebate, with a minimum of zero. Simple payback = net upgrade cost ÷ annual saving. Ten-year net saving = 10 × annual saving − net upgrade cost.
Tankless savings and simple-payback scenarios
These examples hold usage and energy prices constant and compare only annual energy savings with incremental upfront cost.
| Current cost | Reduction | Annual saving | Net upgrade | Payback |
|---|---|---|---|---|
| $600/yr | 10% | $60/yr | $1,000 | 16.7 years |
| $600/yr | 15% | $90/yr | $1,500 | 16.7 years |
| $900/yr | 20% | $180/yr | $2,000 | 11.1 years |
| $1,200/yr | 25% | $300/yr | $3,000 | 10.0 years |
| $800/yr | 15% | $120/yr | $500 | 4.2 years |
| $400/yr | 10% | $40/yr | $2,000 | 50.0 years |
Maintenance, descaling, repairs, financing, service-life differences, fuel switching, distribution losses and future energy prices are excluded.
Worked example: $600 annual cost and a 15% scenario
$600 × 15% = $90 estimated annual energy saving, leaving a modeled $510 annual cost. With a $1,500 incremental installed cost and no confirmed rebate, simple payback is $1,500 ÷ $90 = 16.67 years. Ten years of $90 savings equals $900, so the net result remains −$600.
Run more than one percentage and cost scenario. A quote should separate the baseline replacement from the added cost of the tankless option so the payback denominator is not overstated.
Tankless technologies and fuels are not interchangeable
Whole-home gas tankless, point-of-use electric and whole-home electric products have different input, venting, flow and infrastructure requirements. ENERGY STAR’s current whole-home tankless water-heater material and certified Product Finder cover qualifying gas models; that does not mean every electric tankless model is ENERGY STAR certified.
Fuel switching can change both fixed and variable charges and may require electrical-service, gas-line or venting work. Model those changes separately rather than applying one percentage to the old bill.
Size by temperature rise and simultaneous flow
A tankless heater must raise incoming water to the setpoint while serving the required fixtures. Colder inlet water reduces the flow available at a given output. Add realistic simultaneous fixture flow and use the manufacturer’s temperature-rise chart—not just a headline maximum GPM.
ENERGY STAR’s current gas instantaneous criteria include minimum efficiency and flow requirements, but certification is not a substitute for household sizing, fuel supply, pressure, venting and installation review.
Use incremental cost and current incentives
If a storage heater already needs replacement, compare the installed tankless option with the installed baseline replacement. Include equipment, permits, venting, condensate, gas or electrical upgrades, water piping, controls and commissioning, then subtract only a confirmed current incentive.
The previously published U.S. federal tax credit page for natural-gas, oil and propane water heaters applies to qualifying purchases and installations from January 1, 2023 through December 31, 2025. Do not assume that expired window applies to a 2026 purchase.
Standby loss is removed, but other losses remain
Tankless equipment avoids keeping a storage tank hot continuously, but energy use still depends on hot-water volume, inlet temperature, setpoint, cycling, minimum activation flow and equipment efficiency. Distribution pipes and recirculation can continue losing heat.
A recirculation strategy may improve wait time while adding pump energy or heat loss. Include its controls and schedule in a complete comparison.
Installation and maintenance can decide the outcome
Gas supply, combustion air, vent category, condensate, clearances, freeze protection, water quality and scale management must follow the exact manual and local rules. High-power electric models may require major service and circuit capacity.
Have a qualified installer verify the complete system. Isolation/service valves can support maintenance only when they are approved and compatible with the exact model and installed as directed.
Sources used for assumptions: ENERGY STAR — whole-home tankless gas water heaters; ENERGY STAR — how whole-home tankless gas water heaters work; ENERGY STAR — tankless gas water-heater benefits and savings context; ENERGY STAR — residential water-heater certification criteria.
Frequently asked questions
How much can a tankless water heater save?
There is no universal percentage. Fuel, current equipment, household hot-water use, inlet temperature, distribution and product efficiency matter. Use a product- and household-specific estimate or test a range.
What cost belongs in the payback calculation?
Use the extra installed cost of the tankless option versus the replacement you would otherwise purchase. Include required infrastructure and subtract only a confirmed current incentive.
What is standby loss?
It is heat lost while a storage tank maintains hot water between uses. Tankless equipment avoids tank standby loss, but cycling and distribution or recirculation losses can remain.
How do I size a tankless water heater?
Determine required simultaneous gallons per minute and the temperature rise from incoming water to setpoint, then use the exact manufacturer performance chart and verify fuel or electrical capacity.
Are electric tankless heaters ENERGY STAR certified?
Do not assume so. ENERGY STAR’s current whole-home tankless program and Product Finder cover qualifying gas models. Check the current certified listing for the exact model and category.
Is there a current U.S. federal tax credit?
The ENERGY STAR page for the prior natural-gas, oil and propane water-heater credit states an installation window ending December 31, 2025. For a 2026 project, verify current law and program guidance before entering a rebate.
Does tankless mean unlimited hot water?
It can heat continuously only while demand stays within its available flow at the required temperature rise and the energy supply is adequate. Excess simultaneous flow can reduce outlet temperature.
Related calculators
Water Heating Cost Calculator
Estimate the useful heat needed to warm water, then adjust for heater efficiency and your …
HeatingHeat Pump Savings Calculator
A heat pump moves heat instead of creating it directly. Enter your own annual heat demand,…
HeatingHome Insulation Savings Calculator
Model an insulation and air-sealing project from the heating and cooling portion of your b…