Homeowners considering or already living with a tankless unit tend to ask the same practical questions: how long will it last, is it noisy, what does venting involve and what happens when the power goes out? This FAQ answers them in plain language. Because models, water quality and codes differ, treat the answers as general guidance and check your own manual and local rules.
Independent, general information. It does not describe any particular manufacturer’s products or warranties.
Lifespan
How long does a tankless water heater last?
Tankless units are often described as lasting longer than storage tank heaters, with figures in the range of about 20 years frequently quoted for well-maintained units. Real-world life depends on water hardness, usage, installation quality, maintenance and the specific model. A figure from a brochure is not a guarantee.
What shortens the life of a tankless heater?
- Hard water and scale buildup
- Skipped maintenance and flushing
- Poor installation, such as incorrect venting or undersized gas lines
- Frequent short cycles or very high demand beyond capacity
- Freezing in unprotected locations
- Corrosive air or exhaust issues
What extends it?
- Annual flushing in hard-water areas; see how to flush a tankless heater
- Cleaning the inlet filter
- Installing isolation valves
- Using a water softener or scale control where appropriate
- Following the manual and scheduling periodic professional service
- Keeping the vent and surroundings clear
Are parts replaceable?
Most tankless units are designed so parts such as sensors, igniters and fans can be replaced, which can extend life. Availability varies, so ask about parts support before buying.
Noise
Is a tankless water heater noisy?
Operating noise varies by model and location. Gas units have a fan and burner that can produce a steady hum or whoosh when running, while electric units are typically quieter. Most people notice little in a utility room or garage, but a unit mounted on a bedroom wall may be audible.
Why is my tankless heater making banging, popping or rumbling sounds?
Possible causes include:
– Scale buildup, which can cause rumbling or popping as steam bubbles form
– Water hammer from fast-closing valves
– Loose mounting or pipes
– Fan or bearing wear
– Vent issues
Start with a flush and check mounting. If noises persist, ask a technician to inspect it.
How can I reduce noise?
- Choose a location away from bedrooms
- Mount on a solid wall with vibration-dampening hardware
- Make sure pipes are properly secured
- Consider a model with quieter operation if noise is a priority and compare specifications
Venting
Why does a gas tankless heater need venting?
Burning gas produces exhaust, including carbon monoxide, which must be carried outdoors. Venting must follow the manufacturer’s instructions and local code.
What types of venting are used?
- Metal venting for non-condensing units with hot exhaust
- Plastic venting (PVC, CPVC or polypropylene, where approved) for many condensing units
- Direct vent (sealed combustion), which uses a pipe for intake air and a pipe for exhaust
- Concentric vent kits that combine intake and exhaust in one penetration
Only use vent materials approved for your specific model. Mixing materials or lengths can be dangerous and void the warranty.
Can I vent through an existing chimney?
Sometimes, with an approved liner or kit, but not always. Chimney conditions and sizes matter. A professional should assess.
How far can the vent run?
Each model has maximum equivalent lengths and rules for elbows. Exceeding them can cause problems. Check the installation manual.
Do electric tankless heaters need venting?
No. They produce no combustion gases and need no flue. Read more in our gas vs electric guide.
Is a condensate drain necessary?
Condensing gas models produce acidic condensate that must be drained, often through a neutralizer. Requirements depend on local rules.
Power and Outages
Will a tankless heater work in a power outage?
Most gas units need electricity for the control board, fan and ignition, so they will not provide hot water during an outage unless you have backup power. Ask about battery backup or generator compatibility.
Can I connect it to a generator?
Often yes, if the generator’s output and quality suit the unit. Check the manual and ask an electrician.
Maintenance and Troubleshooting
How often should I service it?
Annual attention is a common recommendation, with more frequent flushing in very hard water areas. Follow your manual.
Why do I get lukewarm water?
Common reasons include demand beyond capacity, cold-water sandwiches, low flow, scale or crossover plumbing. See troubleshooting lukewarm water.
What do error codes mean?
They vary by model. Refer to your manual or manufacturer support, and do not clear safety lockouts repeatedly without understanding the cause.
Efficiency and Cost
Does a tankless heater really save energy?
It avoids standby losses, so many households use less energy than with a tank, but savings depend on usage, fuel and model. See tank vs tankless.
Is it worth the price?
That depends on your priorities and infrastructure. Compare itemized quotes and estimate payback.
Safety
Is a gas tankless heater safe?
When correctly installed, vented and maintained, yes. Carbon monoxide detectors are essential, and gas and venting work should be done by licensed professionals.
What temperature should I set?
Many households use around 120°F as a balance between comfort and scald protection. Lower the setting if children or older adults live in the home.
Installation and Buying
Can I install it myself?
Gas, venting and high-amperage electrical work should be done by qualified, licensed professionals, with permits where required.
What questions should I ask before buying?
See our buyer’s checklist for a complete list.
Questions to Ask Before Buying a Tankless Unit
How to Flush a Tankless Heater and Remove Scale
Frequently Asked Questions (Quick Answers)
What is the single best thing I can do to extend life?
Keep scale under control with regular flushing or water treatment, and follow the maintenance schedule in your manual.
Is a tankless unit louder than a tank heater?
Gas tankless units can be louder because of the fan, but the sound is usually modest. Placement matters.
Can venting be changed after installation?
Changes should only be made by a qualified installer using approved components.
Will it work during an outage?
Usually not without backup power.
Conclusion
Tankless water heater lifespan, noise and venting questions have practical answers: good installation and regular maintenance extend life, noise depends on model and placement, and venting must follow the manual and code. Keep the manual handy, schedule maintenance and rely on licensed professionals for anything involving gas or electricity.
