A cursory search of Google will tell you that the average lifespan of a water heater is 8-11 years. While one shouldn't believe everything that’s stated on the internet there is some truth to this statement. But only some.
When I first started my plumbing career in the 90’s I remember removing water heaters that were installed in the 1950 and 60's. Some of those were still heating water the day I removed them. I don’t see water heaters that are still working 30 or 40 years later anymore. Very rarely will I find one that is still kicking after 20 years. But that doesn't have to be the case.
Much to the chagrin of conventional wisdom water heater manufacturers haven't cheapened the quality of the units produced these days.They really do still “make ‘em like they used to”.
With the constant threat of lawsuits these days they may even be making them better. But the problem doesn't lie in how modern water heaters are made. The problem lies with how they are installed and maintained, or more appropriately, how they aren't installed and maintained.
There are five layers of protection water heaters have against failure and leakage. The first two are provided from the manufacturer.
First, is the anode rod. The anode rod is a long piece of metal which runs almost the full length of the water heater and its job is to disintegrate from the reactive materials and electric current in the water BEFORE your tank does. In most areas and for many water conditions they last about five years before they are completely depleted. If you read the manual that comes with your water heater you will see the manufacturer recommend that the anode be inspected at least annually for deterioration.
Second is the glass lining. Just imagine the inside of your water heater tank being glazed like a piece of pottery. This is a similar process for protecting the steel of your tank. Once the anode rod deteriorates, this glass lining is the only thing preventing the tank from rusting out. On its own, this lining doesn't last very long.
The other layers of protection are provided by the installer of the water heater and mandated by most plumbing codes. The primary one is from proper piping connection. Dielectric unions provide a buffer zone between the steel of the water heater tank and the copper piping which connects the tank to the rest of the plumbing system. When steel and copper are connected and water run through them they begin to share electrons at a rapid rate. We refer to this sharing of electronic bonds as corrosion. Dielectric unions/connections are often overlooked or ignored by installers to the detriment of the water heaters longevity.
The fourth layer of protection is also provided by your water heater installer. In many scenarios a water heater is required to have a thermal expansion tank. If you have a pressure reducing valve, or a back check valve at your meter (most municipalities do) you are required by code to have a thermal expansion tank. This device gives a safe place for the extra volume created by heating water to go. Without this device, every time the water heater turns on to reheat the stored water, it will produce excess pressure/volume which is a stress on the water heater, water piping, and fixtures attached to it (toilets, washing machine hoses, ice maker, etc.).
The fifth layer of protection is provided by you, the operator of the heater. Again, referring to that handy manual which the manufacturer provided you will find all water heaters should be flushed out and drained to remove build up and sediment at least annually. Some manufacturers recommend this every six months! This not only keeps the water heater at full heating capacity, it also prevents minerals and deposits from attaching to the inside of the tank and solidifying causing future damage.
Unfortunately most of the water heaters I see these days are improperly installed. BIg box stores and do it yourselfers just don't have the know how of a licensed professional. As a result a water heater that should be running for 15 to 20 years is dead and gone in only ten. Just because its heating water and not leaking does NOT ensure a plumbing fixture is installed correctly, especially a water heater. The manufacturer recommendations and the municipal codes are there to not only keep people safe but also to ensure they get the full benefit of a properly installed unit.
Learn more about water heaters and water heater replacement at Pathmaker Plumbing.