Understanding Water Heater Expansion Tanks

30 January 2017
 Categories: , Blog


Perhaps the single greatest threat to a residential plumbing system is high water pressure. It can cause a wide range of problems, from leaking pipes, to damaged plumbing fixtures, to broken appliances. Yet few people appreciate the fact that water heaters are a common source of high pressure. If you would like to improve your knowledge of this little known link, read on. This article will discuss the nature of the problem, while also explaining how an expansion tank can successfully eliminate it.

Thermal Expansion

The key factor when it comes to the link between water heaters and high pressure is known as thermal expansion. This term simply refers to the fact that water expands when it gets hotter. And since a water heater represents a closed vessel, this expansion causes the pressure inside of it to rise. This high pressure then communicates itself to your pipes and fixtures every time you turn on the hot water somewhere in your home.

Closed Systems

High water pressure presents an especially damaging scenario for those who live in cities or towns with closed system regulations. A closed system is one in which the water main running into the home is equipped with a one-way valve. The idea here is that this valve prevents water from backing up into the city's plumbing system, thus preventing flooding and unwanted damage to city sewer lines.

For the most part, one-way valves are a good idea, since massive backflows can easily overwhelm municipal water distribution systems, leading to water shortages and other problems. Yet these valves tend to exacerbate the problem of high water pressure. That's because they prevent water from flowing out of your home as a way to relieve this pressure.

Expansion Tanks

Here is where expansion tanks come into play. These auxiliary tanks, which are attached to your water heater, are capable of significantly lowering the water pressure in your home. That's because, as the water in the heater gets hotter and hotter--in other words, as it expands more and more--it can now flow safely into the expansion tank. This keeps the water pressure inside of the heater at a relatively stable level at all times.

When you turn on a hot water tap somewhere in your house, the demand will be supplied by water from inside of the heater. Then an equivalent portion of water will flow from the expansion tank into the heater. In other words, an expansion tank doesn't just help to alleviate problems related to high pressure. It also allows you to maximize the volume of water being producing inside of your hot water heater.