What size hot water cylinder do we need?

What is the best hot water cylinder size for your household? We get asked this question a lot at Cylinder Direct – it’s not something you think about until the time comes to replace or upgrade your current hot water cylinder.

The answer depends on a few factors.

How many people are there in the household?

This is not the only determining factor, but it gives us some initial general guidance. For example, if we were installing a water cylinder where an elderly single person lived alone (and didn’t plan on having anyone else live with them for years to come), we’d look at a smaller cylinder than one used in a larger family. Conversely, if we were installing a cylinder in a home where there were several children, parents and grandparents all living together, we would consider installing a larger cylinder.

The number of people in the household, therefore, is a good starting point.

What are your water usage habits or patterns?

How many showers or baths are taken each day in your home? Do you fill the bath tub each night for children’s baths?

Does everyone shower in the morning, or are showers spread out throughout the day? Do you have shift workers who bathe or shower during off-peak hours? Do you have competitive swimmers, water polo players, surfers, etc in the household who might shower more than once a day?

Do you use a dishwasher or do you wash dishes by hand? How many times a day?

(Note, most dishwashers and laundry washing machines have an internal system for heating water, therefore they don’t draw water from the hot water cylinder.)

How much room do you have in your home for a hot water cylinder?

Hot water cylinders do take up a fair bit of room, so we always consider available space in the decision making. To give you a rough idea of how much space you need for a hot water cylinder, a standard 180L cylinder is approximately 1710mm tall by 490mm wide. In contrast, a 300L tank (popular in larger households) is 1815mm high by 580mm wide.

General guidelines for hot water cylinder NZ size


135 litres

180 litres

250 litres

270 litres

300 litres

Number of people in household






Dimensions HxW

1325 x 490mm

1710 x 490mm

1555 x 580mm

1640 x 580mm

1815 x 580mm

(specs may vary between brands/manufacturers)

At Cylinder Direct we supply and install hot water cylinders from Rheem and Rinnai – two reliable brands we know and trust. We stand by both of these brands (read more on that here) and we often find that the Rheem product selector page on their website is a good place to find more information.

Do we have to keep the hot water cylinder inside?

Changing or upgrading your hot water cylinder is the perfect time to consider whether it’s in the best place in the home and whether it’s worthwhile moving it. Cylinder Direct offers two alternatives that will help free up some room in your house. The first option is to relocate your hot water cylinder from inside the house to outside. There are models that are made specifically to be outside, and we can find a spot that is unobtrusive. The other option is to consider making the switch to a gas continuous flow hot water system.

Get in touch with the knowledgeable team at Cylinder Direct for a no-obligation initial chat and we’ll help you determine what’s best for your home and your budget. Have a look at our Hot Water Cylinders page – then contact us.