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.

How to calculateexpansion tanksize for chilled water system

However, if you’re heating an open-plan living/dining room, often a hydronic system will be more cost-effective over time.

Diaphragmexpansion tank sizing

In short, electric systems are cheaper to install but more expensive to run. Hydronic systems are more expensive to install but cheaper to run.

The smallest area you can reasonably install hydronic underfloor heating is around 40m2. Significantly smaller than this, and it’s probably going to be cheaper to just use an electric system.

In a new slab, the easiest and most cost-effective method to install the pipework is to tie it to the steel reinforcing mesh. Once the mesh has been laid, we can install the pipework, ready for the concrete to be poured. In this case the hydronic pipework is installed within the structural slab.

In this case, we recommend the topping slab to be 90mm thick. There should be two layers of steel mesh – the bottom layer on 20mm chairs, with the hydronic pipework tied on top. Then a second layer of steel should be placed over the pipes which helps stop the concrete surface from cracking. The pipes are generally 16mm diameter, so this arrangement gives you 50mm concrete cover over your pipework.

Pressuretank sizingcalculator

So you’re building your new dream home, and you love the idea of comfortable, radiant heat keeping you warm all winter? Here are 3 things you’ll need to consider before you start building.

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

As a final option you might look into a low-profile system such as Uponor Minitec which can be installed on top of an existing slab and is only 15mm-20mm thick. This type of system is more expensive however.

Surgetank sizingcalculator

Expansion tankcalculation xls

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!)

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

As a rule of thumb, if you’re only heating bathrooms then electric underfloor heating is probably better. The reason is that it’s a small area (usually only 2-3m2) and it’s not in use for long periods of time.

Alternatively, you might pour an additional topping slab over your structural slab. This is common if there is an existing structural slab, or if your floor will have a polished concrete finish – the topping slab has different properties to the structural slab which makes it better for polishing.

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.

If you’re planning to install a solar energy system, the electricity you generate will help power the heat pump. So in that case it can be a cost-effective option as your running costs will be almost nothing.

Chilled waterexpansion tank sizing

If you’re building a new home, chances are you’re pouring a new concrete floor slab. But if you’re remodeling an existing property, you might already have a floor slab.

Expansion tank sizingcalculator metric

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.

You’ll also need to consider which type of heat source you intend to use. In Australia, hydronic radiant floor heating systems are often heated by gas boilers which have the lowest installation cost. However, the price of gas is increasing so running costs are not as low as they once were.

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

Expansion tank sizingrule of thumb

As an alternative, electric heat pumps are becoming more popular, especially for properties without a connection to the gas network. These are more expensive to install than a gas boiler, (normally $5k – $10k more expensive) but are economical to run.

However in Australia, many people prefer not to have heating in their bedrooms and opt to have underfloor heating in just their living room, or only in wet areas like bathrooms.

Ultimately you’ll have to make a decision based on your budget, how long you intend to live in the property, whether you have gas or 3-phase power available, and your preference for renewable vs non-renewable energy options.