How Long Will My Tankless Water Heater Last

how long will my tankless water heater last?

What's the most asked question we get regarding tankless water heaters?

How long will my tankless water heater last? That is the number one question customers ask when we’re discussing tankless water heater installation.

So this plumber has decided to share his answer based on actual experience in the Charleston, SC Lowcountry area.

Please note, the information in this article is based solely on this plumber’s experience – not information from online statistics. This information is also based on this plumber’s geographic location which happens to be the beautiful Charleston, SC Lowcountry area. So if you’re asking this question in Chicago, Illinois this is not going to be your best answer.

Factors that determine your tankless water heater's lifespan.

What factors determine your tankless water heater’s life expextancy? Let’s check it out.

First, you have to consider location. This can be geographic and where the unit is actually installed at your home.

Geographic location is pretty important. In our area (Charleston, SC) we don’t get too many extremely cold winters. So the chances of our tankless water heaters freezing is much less likely than a tankless water freezing in North Dakota. But we do have a lot of moisture. 

Why is moisture important in regards to tankless life expectancy? Because tankless water heaters have a lot of interior components that can be negatively affected by moisture. Metal doesn’t like high amounts moisture. Wiring doesn’t like moisture. Don’t let moisture scare you, because tankless water heaters are designed to be installed outdoors and they work great, but we do have to consider moisture when discussing life expectancy of a tankless water heater.

The other location consideration is where on your property is your tankless located? Most are installed on the exterior of the building or in the garage. We discourage putting them in attics because they’re really hot in the summer and can get extrememly cold in the winter. High heat isn’t great for electronic components. Plus if you get a leak, you run the risk of flooding your home from the top down! We also discourage water heaters from being installed in the living space but this is because of safety. Any gas fixture can create carbon monoxide and anything carrying water can leak. So we suggest sticking to exterior or garage installations. 

Outdoor installations are the most common in our area. Tankless water heaters are designed for outdoor installation. But make sure your tankless is installed in a good location. Too close to the ground and you’ll see the bottom of the unit rusting out quickly. Under a section of roof that dumps water on top of the unit and you’ll see other parts of the unit start to rust as well as interior components corroding.

While tankless water heaters are designed to be outside, they are subjected to weather 24/7. Rain, sun, moisture, wind, hail, cold, heat and yes (although a rarity in our area) possibly even snow. So typically units in a garage tend to last a little longer than an exterior units. But don’t be too concerned, this plumber’s tankless is located outside and it’s just fine.

Tankless water heaters installed in the garage. You won’t have to worry about the weather aspects affecting your tankless water heater’s life expectancy. Typically garage installed units still look brand new when they have to be replaced. So as far as location goes, garage installs are slightly better than exterior installs but not that much better that I’d recommend spending $1,000s more to just to put it in the garage.

Second, what is the water quality at your location? Water quality matters. Excessive sediment, scale, rust or debris in your water is not good. Hopefully your “plumber(s)” didn’t use galvanized piping anywhere in your water piping system. It can stick to the filters and piping causing premature failure. An important reason to service your unit annually. Partially clogged filters make the unit work harder which is bad for the components.

Third, What is the air quality around your tankless water heater’s fresh air intake? Excessive dust, in many forms, is bad for your tankless. Chemical vapors are not good for safety reasons. Some advice, don’t set up a wood working equipment (cutting/sanding) near the air intake. It will clog your filter and lead to premature failure. And never store fuel or open flammable chemicals in your garage, especially if your heater uses room air for combustion.

Fourth, gas piping. Make sure you have an adaquate gas supply to your water heater. Undersized gas piping will make your unit work harder (if it doesn’t shut off on you and spit out an error code). Undersized gas piping will also void the warranty. 

Number five. Make sure your electrical supply is grounded. Connecting your tankless water heater to an improperly grounded supply can cause all kinds of problems to the components and it voids the warranty. Remember, these water heaters are as smart as a computer, so electrical issues can damage the heater. And we’ve seen what a power surge can do to an ungrounded tankless water heater that was only 6 months old – every wire in the unit was fried – it’s a good thing the gas control valve remained closed.

Sixth, who installed your tankless water heater? Did a licensed plumber install your tankless water heater? Ensuring that your unit is properly installed accounts for more life expectancy issues than any other factor. A licensed and experienced plumber who follows code the manufacturer’s guidelines will get you the longest life expectancy. Most of the units we replace prematurely were not installed correctly which helped shorten the life expectancy. Installing or replacing a tankless water heater is not something we recommend for DIY. Tankless water heaters are amazing when installed correctly. 

Finally, do you service your tankless every year? Having your unit serviced annually will be able to eliminate small problems before they become big problems. Lack of annual service is the primary reason we have to replace properly installed tankless water heaters sooner than the 15-20 year mark you read about online.

How long will my tankless water heater last?

Properly installed and serviced annually you can definitely get 15-20 years. Remember there are many factors that determine the lifespan of your tankless water heater. We’ve replaced units between 15-23 years old that were properly installed and serviced annually.

Properly installed but not serviced annually you might get about 10 years. We’ve replaced 8 year and 12 year old units that were never serviced but properly installed. Many factors will determine how long you’ll actually get. You might ask why can’t we just fix a 10 year old heater. Mainly the cost involved. Parts/labor are out of warranty and the repair would cost more than the replacement. 

Improperly installed units may not last a year and they can be a safety hazard depending on how bad the install was. This plumber and many others won’t repair an improperly installed unit because we won’t warranty any repairs on an improperly installed unit so please consider that when deciding on an installer. Units installed too low to the ground or in a location where water dumps directly on them from the roof won’t last 10 years, I’d say you’ll be lucky to get 6 years.

So whether or not you decide to go the annual service route, at least make sure your tankless water heater is installed correctly by a licensed and experienced plumber.

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Steven Dyson

Steven Dyson

Owner of Hanahan Plumbing Co and licensed mechanical contractor since 1997.


Small, family owned and lifelong Lowcountry residents.


Licensed plumbing and gas contractor (M115194).


Over 30 years of experience serving the SC Lowcountry area.

Serving Hanahan, SC & the Surrounding Lowcountry Area

© 2024 Hanahan Plumbing Co.. All Rights Reserved. SC# M115194

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