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Get the cylinder size right and you have reliable hot water without paying to heat more than you use. Get it wrong and you either run out mid-shower or waste energy keeping a too-big tank hot. The right size comes down to how many people are in the house and how you use hot water. Here is a practical guide.
Sizing by Household
As a general guide for a mains-pressure electric cylinder:
- 1 to 2 people: around 135 to 180 litres
- 3 to 4 people: around 180 to 250 litres
- 5 or more people: 250 to 300 litres or more
These are starting points, not hard rules — your habits matter as much as the headcount.
What Pushes the Size Up
- Long or frequent showers, or several people showering close together in the morning
- A bath that gets regular use — baths use a lot of hot water at once
- Multiple bathrooms in use at the same time
- Appliances plumbed to hot water
If your current cylinder runs out and you are constantly waiting for it to reheat, it may simply be undersized for how your household has grown.
Cylinder or Continuous Flow?
Sizing is a cylinder question. If you are weighing up whether a tank is even the right approach, a continuous flow (instantaneous) system never runs out and is sized by flow rate rather than tank volume — but it has trade-offs. Our guide on hot water cylinder vs continuous flow compares them.
Do Not Forget Recovery Rate
Tank size is only half the picture — recovery rate (how fast it reheats) matters too. A smaller tank with a fast recovery can outperform a larger, slow one for a busy household. This is part of why winter feels worse: colder incoming water means slower recovery, which we cover in why hot water cylinders fail in winter.
Get the Right Advice
The best size depends on your specific household, the space available, and whether you are on mains or low pressure. When we quote a replacement, we size it to your actual usage rather than guessing — so you are not left short or paying to heat water you never use.
Hot Water Sizing and Replacement Across Auckland
Water and Gas Worx sizes, supplies and installs hot water cylinders across Auckland. See our hot water services and our areas we service.
Call 0800 322 322 or email service@wgw.co.nz.
Frequently Asked Questions
What size hot water cylinder do I need for a family of four?
As a general guide, a household of three to four people is usually well served by a 180 to 250 litre mains-pressure cylinder. The right figure depends on your habits — frequent long showers, regular baths or multiple bathrooms in use at once push the size up. We size to your actual usage when quoting.
Is a bigger hot water cylinder always better?
No. An oversized cylinder wastes energy keeping more water hot than you use. The goal is to match the cylinder to your household so you have enough hot water with a good recovery rate, without paying to heat water you never touch.
What is recovery rate and why does it matter?
Recovery rate is how quickly a cylinder reheats after you have drawn off hot water. A smaller tank with a fast recovery can keep up with a busy household better than a larger, slow one. In winter, colder incoming water slows recovery, which is why hot water can feel like it runs out faster.
Can I upgrade to a bigger cylinder than I have now?
Usually yes, subject to the space available and your home's setup. If your household has grown and you keep running out of hot water, upsizing or switching to continuous flow are both options. We can advise on what fits your space and usage when we quote.