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How Long Does a Tankless Water Heater Last?

Quick answer: A well-maintained tankless water heater often lasts about 15–20 years, versus roughly 8–12 years for a typical storage tank. Hard water without yearly descaling is the most common reason units fail early, followed by undersizing and freeze damage. Replaceable parts can extend life further. Estimates only; results vary by water and use.

Context: why tankless units can last longer

A tank holds water constantly, so its steel shell corrodes over time and eventually leaks. A tankless unit holds little water and has more replaceable parts — sensors, igniters, fans, valves — so many repairs do not end the unit's life. The heat exchanger is the part that usually decides when to replace.

Terms

Heat exchanger: where the burner or element transfers heat to water. Scale and corrosion here are the main wear points.
Scale: minerals from hard water that coat the exchanger.
Duty cycle: how hard and how often the unit runs; undersized units run near maximum more often.
Warranty term: heat exchanger warranties are often longer than parts warranties.

Typical life by type (example ranges)

Type	Example lifespan
Gas tankless, maintained	15–20+ years
Electric tankless	10–20 years
Gas tankless, hard water, never flushed	7–12 years
Storage tank (gas or electric)	8–12 years

What shortens life

Skipped descaling in hard water.
Undersizing, which keeps the unit at full firing rate.
Freeze damage, especially outdoor units during power outages.
Poor combustion air — dust, lint or chemical fumes near indoor units.
Sediment without an inlet filter clean.

Process: how to extend life

Test your water hardness (test strips or utility report).

2. Flush on a schedule that matches hardness — see how to flush.

3. Clean the inlet filter.

4. Keep air intakes clear.

5. Book licensed service when error codes repeat.

6. Size correctly from the start with the size calculator.

Worked example

Figures below are illustrative examples (2026-10-29), not quotes or guarantees.

Assumptions: gas unit, moderate hard water, $1,500 unit + $1,800 install.

Maintained: yearly flush at ~$15 supplies; unit lasts 18 years. Cost per year of hot water hardware: ($3,300 + $270) ÷ 18 ≈ $198/yr.
Not maintained: unit fails at 10 years. ($3,300) ÷ 10 ≈ $330/yr.
Tank comparison: $1,800 installed, lasts 10 years ≈ $180/yr, before energy differences.

The maintained tankless lands close to the tank on hardware cost per year, with energy savings and endless hot water on top. Compare in tankless vs tank.

Signs of end of life

Repeated heat-exchanger error codes after flushing.
Visible leaks from the exchanger.
Repair quotes approaching a large share of replacement cost.

FAQ

What is the most common failure?

Scale build-up in the heat exchanger from hard water.

Is it worth repairing an old unit?

Often yes for sensors or igniters; less so for a failed exchanger out of warranty. Ask a licensed pro.

Does an electric unit last longer?

It has no combustion parts, but elements and scale still limit life.

Does a softener help?

It reduces scale and usually helps lifespan in hard-water areas.

Safety and code reminders

Gas, venting, combustion air, condensate disposal and high-amperage electrical work all carry real safety risks, including carbon monoxide, fire, scalding and shock. They are also governed by local code and permits that differ between towns and provinces or states. Treat every step on this page as preparation for a professional visit, not as instructions to do the work yourself. Keep the manufacturer's manual for your exact model, set water temperature with scald risk in mind (120°F is a common household target), and stop and call a licensed professional whenever something is unclear.

Quick reference: typical fixture flow rates

These example flow rates help you translate everyday use into the GPM numbers used throughout this site. Check the rating stamped on your own fixtures, as older fixtures often run higher.

Fixture	Example hot-water flow
Low-flow showerhead	1.5–1.8 GPM
Standard showerhead	2.0–2.5 GPM
Bathroom faucet	0.5–1.2 GPM
Kitchen faucet	1.0–1.8 GPM
Dishwasher	0.8–1.5 GPM
Washing machine (warm)	1.0–2.0 GPM
Bathtub fill	2.0–4.0 GPM

Add only the fixtures that genuinely run at the same time. Running the dishwasher or laundry outside shower hours is the simplest way to stay within a unit's capacity.

Questions to ask a licensed installer

Bring these questions to every quote so you can compare them fairly. Good installers welcome them, and the answers often reveal hidden costs before work starts.

What peak GPM and temperature rise did you size this unit for, and what inlet water temperature did you assume for winter?
Is my existing gas line, meter or electrical panel large enough, and if not, what exactly needs upgrading and what does that line item cost?
What venting route will you use, how long is it, and does it meet the manufacturer's instructions and local code?
Does the quote include a permit, isolation (service) valves for future flushing, a condensate drain if needed, and removal of the old heater?
What are the labour warranty and the manufacturer's heat-exchanger and parts warranty terms, and do they require registration or yearly professional service?
How long will the install take, and will there be a period without hot water?

How to read the numbers on this site

Every figure on TanklessMath is a planning estimate. Ranges reflect typical North American examples as of 2026-10-29 and will differ with your region, home, fuel prices and installer. Equipment ratings vary by model, so always check the specification sheet for the exact unit you are considering. When our example and a licensed installer disagree, trust the installer who has seen your home.

Next steps

Write down your peak fixtures, coldest incoming water temperature, fuel type and possible locations, then ask at least two licensed installers to confirm sizing, venting, gas or electrical capacity, permits and local code. Compare written quotes line by line so the unit, labour, materials and upgrades are separated. Questions about this site: hello@charlandandco.com.