Hot water tanks are still the most common method of providing domestic hot water for showers and washing however hot water tanks have the shortest service life of the major mechanical systems of the home. I’m often asked by clients some common questions about hot water tanks.
Why Do Hot Water Tanks Have Such Short Lives?
The primary failure method for hot water tanks is to spring a leak and this leak is typically caused by erosion of the inner pressure tank. Essentially, oxygen molecules in the water supply will cause the metal in the tank to rust. The reason hot water tanks have shorter lives than other water/metal mechanical systems however has to do with some additional unique characteristics of a hot water tank.
The speed at which metal will ‘rust’ will speed up when there is a fresh source of oxygen, chemical reaction catalysts (like natural salts and minerals) and even heat and pressure can speed up the process. As hot water tanks have a constant supply of fresh oxygenated water, and generate heat under supply water pressure, rust is inevitable. The real wild card however in how long a hot water tank will last is based on the mineral content of the supply water to the home. This mineral content can speed up rusting in the tank censurably and is highly variable in different communities.
How Long Does a Hot Water Tank Last?
Predicting the failure of mechanical equipment is a statistical experiment. On the short end, tanks have been known to fail in as little as 8 years, and in some cases, I’ve seen original hot water tanks in 20-25 year old homes. The industry ‘average’ for hot water tank life is usually considered about 10-12 years.
When Should I Replace My Hot Water Tank?
This question is all about managing risk. If you absolutely cannot risk a water leak from a hot water tank, you should be pretty safe replacing it every 8 years (by pretty safe, that still means a small risk of premature failure). As a home inspector, I start to warn people of probable failure when the tank is about 10 years old and recommend replacement on all tanks over 12 years of age.
Another part of the risk to manage is what happens if there is a leak. In many house basement mechanical rooms, there is a drain a few feet away ready to collect water from a potential leak. In these houses, there is less risk of damages from a leak. However if you live on the 4th floor of a wood frame condo and there is no drain around your hot water tank, repairs to the building below you could be very expensive in the event of a leak.
How Can I Tell the Age of my Hot Water Tank?
This is one of the most frustrating parts of my job as for some reason the labelling requirements for hot water tanks don’t include an obvious date code. Every manufacture uses a different combinations of letters and numbers (usually in the serial numbers) to determine the month/year or week/year of manufacture. Fortunately, most of these codes can be looked up by inspectors or home owners on the internet but for some brands such as Sears Kenmore units (which are made by other factories), the code system can be nearly impossible to determine. With experience however, home inspectors can observe other components like gas valves, installation methods, and temperature pressure valves to get a closer idea of the date of the unit.
Do Tankless Hot Water Heaters Last Longer?
Tankless hot water heaters still have metal, oxygenated water, oxidization catalysts, heat, and pressure and are also slowly working their way to failure. There has not been a good history of these units to predict life spans however most home owners are being cautioned to consider the same 10-12 year life spans.
While hot water tanks have a short life compared to most other mechanical systems, they are much less expensive than most mechanical systems. Installation costs can vary as different municipalities may have different permit and code needs but it is often comparable to the price of a ‘good’ dishwasher.
If you are unsure about the age or condition of your hot water tank, call your local home inspector, service technician, or a competent handyman to help you know if your tank is safe and solid.