What happens if you don't have an expansion tank?

Author: Fay Considine  |  Last update: Sunday, December 28, 2025

As plumbers know, the expansion tank equalizes pressure throughout the plumbing system by providing a space for hot water to flow into. Without an expansion tank, pressure would be distributed to the entire plumbing system, straining it and decreasing its lifespan.

Is an expansion tank really necessary?

An expansion tank is required on the supply line coming into the tank to reduce the tank stress which will shorten the tank's useful life. An alternative to the expansion tank is an approved pressure relief valve assembly. These devices are required on closed systems, which is public water.

What if I don't have an expansion tank?

Now that might not seem so bad but if you don't have an expansion tank, a closed system doesn't give expanded water any route for escape, causing damage to your home's water heater and plumbing. Here's what we mean: When water is heated inside your water heater, it expands. This is called “thermal expansion”.

Does a 30 gallon water heater need an expansion tank?

Whether or not your water heater requires a hot water tank expansion tank to operate depends on what type of plumbing system you have. Homes either have an open or a closed water heater plumbing system and if yours is the latter, then you'll need an expansion tank to allow your water heater to operate.

How do I know if my water heater needs an expansion tank?

1. If you have a closed system. 2. If you have a pressure regulating valve or a check valve. 3. If you have noticed fluctuating high and low water pressure. 4. If your local city codes require you to have an expansion tank. 5. If you want your water heater to last as long as possible.

How to tell bad expansion tank

Is an expansion tank required by code?

If you are on a "Closed" loop water system, you will be required to have a Thermal Expansion Tank installed on your water heater, the next time it is replaced or repaired.

What happens when an expansion tank goes bad?

If your hot water expansion tank is failing, the following will occur. The relief valve drips during the water heater recovery period, despite no water usage. The water heater tanks in your home fail prematurely. You will hear a metal cracking noise stemming from your water heater when pressure is relieved.

What size water heater requires an expansion tank?

Water heater capacity greater than 60 gallons should meet the following requirements: Water pressure less than 50 psi — 2-gallon expansion tank. Water pressure 50-60 psi — 3.2-gallon expansion tank. Water pressure greater than 60 psi — 4.4-gallon expansion tank.

How do I tell if I have a closed water system?

If your home has a Backflow Prevention Device, Pressure Reducing Valve (PRV), re- circulating pump with check valve, or anything else that prevents backflow of water installed, its plumbing system is considered "closed".

How much does it cost to install an expansion tank?

According to Forbes, the average cost of expansion tank installation is $220 (CAD 270) for materials and labor, with most homeowners spending between $90 and $350 (CAD 122 and CAD 473). Expect to spend between $40 and $200 (CAD 54 and CAD 270) for the tank itself, excluding the cost of labor.

Why do some water heaters not have expansion tanks?

However, an expansion tank may not be necessary if your water heating system has an open plumbing system, such as an open-loop solar heating system or a gravity-fed system.

Why doesn't my house have an expansion tank?

Many homes built before certain plumbing codes were enacted may not have an expansion tank, as they were not a standard requirement. In older systems, open water systems allowed the expanding water to flow back into the city's water lines.

What psi should an expansion tank be set at?

Expansion tanks are pre-charged with a 40 PSI air charge. If the inlet water pressure is higher than 40 PSI,the expansion tank's air pressure must be adjusted to match that pressure but must not be higher than 80 PSI. *Highest recorded inlet water pressure in a 24-hour period of regulated water pressure.

Can I install an expansion tank myself?

Expansion tank installation may be required by your local building codes when installing a new water heater, or it may be a retrofit project. Either way, it will involve splicing into the cold water delivery pipe above the water heater, and should only be taken on as a DIY if you have experience with plumbing work.

Can an expansion tank reduce water pressure?

No, expansion tanks do not increase water pressure. They handle thermal expansion from the heating process and reduce excessive water pressure. This process helps safeguard your plumbing system from damage by thermal expansion.

Does every house have an expansion tank?

If your home has a “closed” plumbing system, then yes, you'll need an expansion tank. You see, homes have either an open or a closed plumbing system. A closed plumbing system prevents water from flowing in the reverse direction (i.e., water won't flow back into city lines once it enters your home's pipes).

How do I know if I have a water leak underground?

Signs of an underground water leak
  1. Sudden increase in water usage and costs. ...
  2. Cracked areas or bulges of pavement. ...
  3. Unpleasant smells. ...
  4. Low pressure in the water supply. ...
  5. Dirty water. ...
  6. Sounds from pipes. ...
  7. Thermal imaging. ...
  8. Acoustic leak detection.

What states require expansion tanks on water heaters?

The California Plumbing Code (Section 608.3) and the California Mechanical Code (Section 1005.0) require a thermal expansion tank to be installed on all closed plumbing water heating systems.

How do you tell if you have a closed plumbing system?

If you notice fluctuating water pressure or strange noises in your pipes, these could be indicators of a closed system. Understanding your plumbing setup can help you address any issues more efficiently and maintain a healthy system.

Does a 20 gallon water heater need an expansion tank?

Expansion tanks are required by code in all new water heater installations in closed systems. A closed water system uses check valves, backflow prevention devices, pressure-reducing valves, or other devices on the supply line to prevent water from being sucked back into the municipal water supply.

Why do I suddenly need an expansion tank?

When extra pressure builds up in the hot water system, it could cause pipes to burst, resulting in costly repairs and even greater risks if someone gets hurt. With an expansion tank installed, excess pressure is diverted away from pipes and other components which can help prevent accidents and damage.

How much does it cost to install a water heater expansion tank?

A water heater expansion tank costs $150 to $450 on average, with a national average of $325. The total cost depends on the size and type of tank. A water heater expansion tank costs an average of $325 to install, and most people pay between $150 and $450 for the task.

Should an expansion tank be full of water?

No, an expansion vessel should not be full of water. It should contain two separate chambers, one for water and one for air. The air chamber is separated from the water chamber by a rubber diaphragm.

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