What size hot water system do I need?

Fast read

When it comes to hot water storage systems, size is important. A system that is too small will result in frequent run-outs of hot water. At the same time, a system that is too big will waste energy and money.

Consider your hot water usage patterns to find the right size system for your household. First, look at the total amount of hot water and how you use it. Adding 10-20% is also recommended to account for days when you may use more than usual.

Household size should also be taken into consideration. With a recommended size of < 100 Litres for a 1-person household, around 250 Litres for a 2-person household, approx 250-300 Litres for a 3-person household, and between 300 and 450 Litres for a 4 to 5-person household.

What is the best size hot water system for my home?

Every household’s hot water usage varies. This is why ensuring you get the right size system if you get a new hot water storage system is essential. The hot water within a tank is affected by stratification. This simply means that the water temperature is affected by its location in a tank. The higher the water in the tank, the hotter it will be. Alternatively, the lower the water is, the cooler it will be.

Does size matter?

Size does matter when it comes to hot water storage systems. There are two reasons why this is the case. First, if your system is too small, you will run out of water regularly. On the other hand, if your system is too big, you will spend unnecessary energy heating the water. So how do you know what size tank is best for you?

Man working on a large hot water tank
Determining the appropriate size and location of your hot water storage ensures the most efficient use of energy

How to find the right size hot water system?

Also, when shopping for your new hot water storage system, there are three primary considerations – the technology, the volume and the capacity it can deliver.

Heat pumps are the way to go for larger systems

Nowadays, we recommend a heat pump and tank system as the best environmentally friendly technology to make hot water. The reason is that heat pumps use a low amount of energy compared to other methods of heating hot water. They can also be interlinked with a solar system and battery, so we can use renewable energy to heat our water.

What does the volume amount refer to?

Volume refers to the amount of water the tank can hold simultaneously. This is usually what the tanks are advertised as, a ’50L tank’, which means the tank can have 50 litres of water. However, the volume of a tank does not need to be the amount that can be provided at one time.

For example, it can be okay if you have a 50L tank but usually use 60L of hot water daily. This is because if you use 20 litres of water three times spread out throughout the day, the tank can refill, reheat and provide enough water. Unfortunately, such a small system can not be purchased with heat pump technology, and a simple electric tank is the best option in such a case. 

Find out how much you use in a single go

This is where the capacity of water the tank can deliver at one time is more critical. If you find how much water you and your family use throughout the day, you can save money and energy by purchasing an appropriate tank for the family’s needs. 

To calculate your daily needs, please consider that a decent 7-minute shower uses between 60 and 70 litres of water, of which about 40 comes from the hot water tank and the rest from the cold water supply. Hand washing the dishes depends on the unique method, but allow about 40 litres of hot and 30 l of cold water – to mix. Depending on how full you like, a bath can use between 70 and 180 litres of water, with about 2/3 coming from the hot water supply.

Please also consider which time of the day the various family members use the hot water and allow for the time it takes to reheat it. For example, heat pumps take about 1 hour to heat 100 litres of water.

hot water storage tank next to inverters
Your energy consumption patterns will dictate the appropriate hot water tank to be installed

Considerations

So, to correctly size a hot water storage system, you need to find out about your water consumption patterns. Whether you find this by using your water meter, checking consumption over a week, allowing 50% cold and 50% hot water supply, or attaining a professional for advice is up to you.

Usually, we recommend adding 10-20% of your regular water consumption when purchasing a storage system to account for days when you may use more than usual, as you do not want to run out.

By doing this, you can ideally find the right sized hot water storage system for your home, saving you energy in the long run. If you live in a multi-person household, the general recommendation regarding tank size is as follows:

Number of people in a household 1 Person   Household 2 Person   Household 3 Person   Household
 4-5 Person   Household
The recommended size of a holding tank < 100 Litres < 250 Litres < 250-300 Litres <300-450 Litres
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