Hot Water Cylinder Sizes: What Size Do You Need for Your Home?

Hot water cylinder sizes are measured in litres, and picking the right one is the difference between a hot shower for everyone and a lukewarm one for whoever's last in the queue.

This guide covers the sizes most Kiwi homes use, how many people each one suits, and how to check it will actually fit. It's aimed at Auckland homeowners and landlords replacing an old cylinder, renovating, or tired of running out of hot water by 8am.

How to work out the right size

The simplest starting point is the number of people living in the house. The BRANZ Level guide to storage cylinders puts typical use at 40 to 60 litres of hot water per person per day. Multiply that by your household and you've got a rough daily figure. Then adjust for how you actually live:

• Shower habits: long showers, teenagers and back-to-back morning routines all push you toward the upper figure.
• Baths: a spa bath or regular deep baths can empty a smaller cylinder in one go.
• Mains pressure: higher flow from the tap means more hot water used per minute, so households upgrading from low pressure often go up a size.
• Guests and growth: if a baby is on the way or the in-laws visit often, size for that.

Bigger isn't automatically better, though. An oversized cylinder keeps water hot that nobody uses, and you pay for that heat every day.

Small hot water cylinder options

A small hot water cylinder can make a lot of sense for a studio, a sleepout or a minor dwelling with its own kitchen and bathroom. Units from around 45L are available and can sit in a compact cupboard or under a bench. Pipe Fix also uses 45L cylinders as temporary hot water during repairs, which shows how far a small unit can stretch for a short stint. Most small hot water cylinder NZ models are built with one person in mind, so a full-time household of two or more will usually run them dry too quickly.

135 litre hot water cylinder

A 135 litre hot water cylinder suits a couple or a single person with a single bathroom. It's also a common size in older Auckland units and townhouses where cupboard space is tight. Many 135L hot water cylinder models are the same width as a 180L, just shorter, which makes them handy where height is the limit.

180 litre hot water cylinder

If you're not sure, a 180 litre hot water cylinder is the safe middle ground. It handles most families of three or four with one bathroom, and it's the size most replacements in Auckland go back in at. It's also widely available in both low and mains pressure versions, which keeps choice and pricing competitive.

250 litre hot water cylinder

Step up to a 250 litre hot water cylinder when you've got four or five people, two bathrooms in use at the same time, or teenagers who treat a shower like a holiday. A 250L hot water cylinder is noticeably wider or taller than a 180L, so measure before you commit.

300 litre hot water cylinder

A 300 litre hot water cylinder is for big households, homes with a spa bath, or anyone running a home business that uses hot water. It needs a decent cupboard or an outdoor position, and it costs more to keep hot, so it only earns its place if you'll actually use the capacity.

180 litre hot water cylinder dimensions and fitting it in

Capacity is only half the story. The cylinder also has to fit the space, with room for valves, pipework and a safe tray underneath. As an example, a Rheem 180L mains pressure stainless cylinder sold in NZ measures 560mm wide and 1,295mm tall, while the 135L version of the same range is 560mm wide and 1,010mm tall. Other brands differ, so always check the spec sheet for the exact model.

When you're checking 180 litre hot water cylinder dimensions against your cupboard, measure:

• Width and depth: allow extra space around the cylinder for valves and access.
• Height: include the safe tray and the pipe connections on top.
• Door opening: the cylinder has to get through the door, not just fit inside once it's there.

Diameters vary a lot across the market, from roughly 460mm to 810mm. Shorter, wider cylinders tend to lose less heat than tall, slim ones, so if you have the floor space, a squat model can be the more efficient pick.

Other things that change the size you need

A few situations change the maths:



• Heat pump hot water: these still store water in a tank, so sizing follows similar rules, but recovery times can be slower. Ask about the model's reheat speed.
• Gas continuous flow: there's no storage tank at all, so size is about flow rate rather than litres.
• Outdoor cylinders: moving the cylinder outside frees up your cupboard and can open up bigger size options.
• Night rate power: if your cylinder only heats on cheaper overnight power, you'll want enough stored to last all day.

Signs your current cylinder is too small

Get the size right the first time

Choosing a size is easier with a plumber standing in front of your cupboard. Pipe Fix's licensed plumbers can look at your household, your current setup and your space, then recommend the size that fits both. Our hot water cylinder installation service covers supply, fitting, valves and testing, with most jobs done in around half a day. If budget is the next question, our guide to [hot water cylinder replacement cost] breaks down typical Auckland prices.

Call 021 217 2782 to talk sizing with the team. Not sure what you've got now? The label on the side of the cylinder lists its capacity. Snap a photo, send it to info@pipefixplumbing.co.nz, and the team will suggest what to go with.

Frequently asked questions