In the rare situation that an excessive amount of pressure builds up in the tube it can create an unsafe situation and/or damage to the enclosure. Pressure build-up could be due to the buildup of gasses from a chemical reaction like something catching on fire, or from a slow leak into the enclosure while at depth followed by a quick return to the surface. The PRV automatically releases any excess pressure built up inside a watertight enclosure. It works automatically to relieve pressure, and it also works manually, like our original vent.

AMTROLExpansion Tank SizingChart

To protect the water heater, pipes, and other system components from excessive pressure when heating water, an expansion tank is added. A simple device, it is nothing more than a tank with a bladder (thick balloon) inside. The space between the bladder and the inner wall of the tank is pre-charged with air to closely match the neutral pressure of the system BEFORE the water is heated. Then, when heat is applied and the pressure goes up, the expanded water volume flows inside the bladder. The air outside the bladder compresses against the tank walls, providing the cushion needed to protect the rest of the system.

If you have questions about equipment size, water heaters or expansion tanks, you should talk to your manufacturing representative to ensure that you’re selecting the best equipment sized correctly for your application.

As a rule of thumb, a thermal expansion tank should be about 10% of the total water heater volume. Let’s take some examples:

Sizing a thermal expansion tankaustralia

When you look a water heater in a large building or even a home, you may notice a much smaller tank close by. That small tank is a thermal expansion tank. An expansion tank in this application is a vessel design to accept additional system volume resulting from heating water. Water is incompressible and, when it is heated, it expands. If this happens in a system with a fixed volume of pipes and equipment, you will quickly discover the weakest point in the system as water begins to spray through it. (Hopefully, it is the pressure relief valve releasing water!)

Expansion tank sizingrule of thumb

The Pressure Relief Valve is an important safety mechanism for our locking watertight enclosures and also adds a few features to the enclosures.

Why is it needed for safety? Our watertight enclosures have come with a manual vent that has worked great for years. But, our next generation watertight enclosures have a locking cord that secures the flange to the tube and prevents the end cap from coming off.

Sizing a thermal expansion tankcalculator

The PRV is designed to work with the updated Vacuum Plug and Backfill Adapter. Check out those product pages for more details and usage guides! Note that if you already have a vacuum plug, you will need the updated version to be compatible with the PRV.

Chilled waterexpansion tank sizing

The Pressure Relief Valve (PRV) automatically releases any excess pressure built up inside a watertight enclosure. It works automatically, but it can also be opened manually or used to perform a vacuum test on your enclosure! We strongly recommend using the PRV on our locking watertight enclosures.

The PRV has an M10 thread so that it can be mounted to any of our watertight enclosure end caps. It can be used in a few different ways:

AMTROLexpansion tank Sizingpdf

Sizing a thermal expansion tankpdf

Remember, this is just a rule of thumb. In addition to water heater volume, an engineer will consider other factors when sizing and selecting a thermal expansion tank, such as entering and leaving water temperatures and minimum and maximum pressures. The expansion volume may then be calculated and a tank selected based on acceptance volume and overall volume. In most cases, the engineered expansion tank size will be smaller than the 10% of the water heater volume, but, for budgeting/planning purposes, this estimate will get you in the right ballpark.

In the rare situation that an excessive amount of pressure builds up in the tube it can create an unsafe situation and/or damage to the enclosure. Pressure build-up could be due to the buildup of gasses from a chemical reaction like something catching on fire, or from a slow leak into the enclosure while at depth followed by a quick return to the surface. The PRV automatically releases any excess pressure built up inside a watertight enclosure. It works automatically to relieve pressure, and it also works manually, like our original vent.

The PRV is designed to work with the updated Vacuum Plug and Backfill Adapter. Check out those product pages for more details and usage guides! Note that if you already have a vacuum plug, you will need the updated version to be compatible with the PRV.

The Pressure Relief Valve is an important safety mechanism for our locking watertight enclosures and also adds a few features to the enclosures.

Expansion tank sizingcalculator

Why is it needed for safety? Our watertight enclosures have come with a manual vent that has worked great for years. But, our next generation watertight enclosures have a locking cord that secures the flange to the tube and prevents the end cap from coming off.

The PRV has an M10 thread so that it can be mounted to any of our watertight enclosure end caps. It can be used in a few different ways:

We are proponents of sustainable and efficient hydronic heating and cooling building solutions, which are at the heart of commercial green building.

David Swinson has worked for Heat Transfer Sales for over 35 years. His knowledge of HVAC and plumbing equipment is vast.