The biggest drawback to installing a thermal expansion tank is the maintenance that goes along with it. Amtrol, a leading manufacturer of thermal expansion tanks states that yearly maintenance is required. As the tanks gets older more frequent maintenance is required. Currently the average lifespan of an AO Smith water heater in Kansas City is 21 years.
With a conservative price of $89 per inspection, over the course of 21 years it could add up to $1,869.00 just for the maintenance. Thermal Expansion tanks have an average lifespan of less than 3 years as reported on water heater database which is due to lack of maintenance. They can last for over 10 years if they don’t sit full of water. Once an expansion tanks fills with water it can fail within a few months.
Even more upsetting is that thermal expansion tanks have not shown any sign that they actually increase the lifespan of your water heater. Unfortunately they have shown a near 100% reported failure rate at the time of replacement or repair.
Maintenance description provided by the Manufacturer
“A professional plumber should check the complete system, including the expansion tank, yearly and more frequently as the system ages. Checking the precharge allows a small quantity of air to escape and can result in an insufficient air charge. Always check the precharge while the tank is isolated and empty of water, and be sure to maintain the proper precharge whenever the tank is inspected.”
Drawbacks of a thermal expansion tank
- An increase in water pressure will cause the expansion tank to fill with water. This is frequently caused by failing PRV’s or improper inflation of the expansion tank.
- If the expansion tank fails it can cause major flooding. One incident in a commercial building caused over $125,000 worth of damage.
- Electrolysis frequently occurs at the top of the thermal expansion tank, despite many of them using a stainless steel nipple. This is why many expansion tanks that have filled with water look like the tank pictured above.
- Water Pressure can fluctuate in many residential areas based on usage during a particular time of day which makes calibration nearly impossible even when performed by a licensed plumber. So if you have a thermal expansion tank you should also have a PRV.
- The requirements for expansion tanks are too vague. The code is written to require a thermal expansion tank on all closed loop systems. However, if you have a new PRV and your water pressure is below 80 psi an expansion tank is not necessary.