One of the most common home inspection deficiencies is the comment of "no thermal expansion device installed". What is a thermal expansion device and why should one be installed? Is this really an issue or is this write up just another case of "a pain in the neck smarty pants" home inspector trying to show off for clients by raising inane and esoteric concerns "raining on the parade" and "killing the deal"?
Way back in 1974, Congress passed the Safe Water Drinking Act (Yes, Virginia that was over 30 years ago!). The act mandated that municipalities protect public water systems from contamination from users of the water system due to backsiphonage of water into the public system from the plumbing systems of private customers. To prevent such contamination, the law required that backflow prevention devices be installed between public water systems and private users. Ever since the act was passed, cities and counties have been upgrading water systems by replacing water meters and installing backflow preventers. This is an ongoing effort and in my home county, this work continues.
How can a backsiphonage occur? Imagine you are mixing pesticides with water in a bucket in your backyard; you have dropped the hose into the bucket to fill it. From out of nowhere, you hear the roar of your neighbor's teenage son's super hopped up car flying around the corner. The car comes to a sudden stop as it cleanly shears the fire hydrant in your front yard from the water main! As water flows from the break in the main, it creates suction on the system and the pesticide laden water you are brewing in your backyard gets sucked from the bucket you are filling back into the public water system thus contaminating the system. This is a bad thing. Other than your neighbor's reckless teenage son, you probably don't want to kill your neighbors!
If there was a backflow valve installed on your system, the above incident would not happen as the backflow valve would prevent the water in your plumbing system from flowing back into the public system. So, what does all this have to do with thermal expansion devices?
Once a backflow preventer is installed (or a pressure regulating valve) on a plumbing system of a house or other building, a "closed system" is created. When water is heated its density decreases and its volume expands, and you may remember from your 8th grade General Science class, that water cannot be compressed. So, when water is heated in a storage tank type water heater that is connected to a closed plumbing system there is nowhere for the water to expand. A means of thermal expansion is needed to relieve the expansion and prevent damage to the plumbing system, such as leaks in pipes, rupturing of the storage tank of a water heater or worse collapse of the internal flue of the water heater.
Given that installation of a means of thermal expansion device is usually relatively inexpensive and an easy enough task for a licensed plumber, it is a wonder how much blood is spilled over this issue in contract negotiations!!! Check with your favorite plumber and you will find the cost to cure this deficiency to be in $125-250 range. Hardly, enough to draw a line in the sand and lose the house you love if you are the buyer or lose the sale you want/need if you are the seller! But, many are going to rise and fall on what they see as "principles": It's grandfathered"; "Its not a code requirement." etc, regardless of the facts!
Many get confused on whether the need for a means of thermal expansion is a building code issue or not, and well it depends: What codes have been adopted by your state or local jurisdiction? When was the water heater installed? Has the water heater been recently replaced requiring it to be in compliance with current code? Is it a closed system? Has the city/county water service installed a backflow preventer on the line? Is there a pressure regulating valve installed?
But the debate about whether or not the need for a means of thermal expansion is a code issue is not the issue. Like so many concerns that are noted in a home inspection, SAFETY is the issue. The fact that a certain condition might be "grandfathered" does not render it safe! And whether you are a home inspector or a real estate agent, concerns for the safety of your clients should always guide your approach and the information you provide.