Plenty of New Zealand homes still run their hot water from a low-pressure cylinder. It's the system BRANZ describes as the traditional hot water supply for New Zealand houses: a tank in the roof feeding a cylinder, with a vent pipe through the roof. Then the renovation starts, someone falls for a wall mixer and a rain shower, and the question lands: will it actually work here?
The honest answer is that it depends on your pressure, not on the word "mains" on a box. This guide shows you how to tell what you've got, what a mixer's working-pressure rating means, how ours are rated, and why unequal pressure makes a shower swing hot and cold. Then it lists the decisions to make with your authorised plumber before you buy.
Updated 14 October 2026. Pressure figures for hot water systems come from BRANZ and Rinnai New Zealand, linked below. Our ratings come from our product specifications and factory technical sheets.
Why Trust InVogue Mirrors & Bathware? InVogue is a mirror and bathware brand trusted in over 20,000 homes, specialising in LED bathroom mirrors and mirror cabinets. The recommendations in this guide come from bathroom design principles — proportion, balance and light — rather than passing trends.
Plumbing work: every tap, mixer and shower must be installed by an authorised plumber, and the work has to meet the New Zealand Building Code (clause G12, Water Supplies). This guide helps you plan and ask the right questions. It is general information, not installation instructions.
Quick Answer
A mains-pressure mixer can work on low-pressure hot water, but only if the pressure at the tap is inside the mixer's rated range, and even then it will run gentler than on mains.
- Our mixers and showers are rated for a working pressure of 0.5–8 bar (50–800 kPa), the same in all six finishes.
- BRANZ puts low-pressure systems at about 30–120 kPa, and mains-pressure systems at typically 350–700 kPa. So some low-pressure homes sit inside our range and some fall below it.
- A header tank in the roof, a vent pipe through the roof, or hot taps weaker than cold all point to low pressure.
- With low-pressure hot and mains cold (unequal pressure), any single-lever mixer finds it hard to hold a steady temperature.
- Ask your authorised plumber to measure both sides before you buy. If the hot is under 50 kPa, our mixers are the wrong choice for that system.
Low Pressure vs Mains Pressure vs Unequal Pressure
There are three set-ups worth knowing, and the difference between them is where the pressure comes from. In a mains-pressure system, the hot water cylinder runs at the pressure of the incoming supply. In a low-pressure system, the hot water's pressure comes from height: a tank above the cylinder, or a valve that cuts the mains down to a level the vent pipe can hold. Unequal pressure is what you get at the tap when the hot is low pressure and the cold comes straight off the mains.
| System | Typical pressure | What it usually looks like | Source |
|---|---|---|---|
| Mains pressure | 120–1,400 kPa, typically 350–700 kPa | A sealed cylinder fed from the mains. No tank in the roof and no vent pipe | BRANZ, updated 27 Feb 2026 |
| Low pressure (header tank) | 30–120 kPa (3–12 m head) | A cold water tank in the roof space feeds the cylinder; a vent pipe rises through the roof | BRANZ |
| Low pressure (pressure-reducing valve) | 30–120 kPa (3–12 m head) | A valve reduces the mains pressure for the cylinder; it still has a vent pipe | BRANZ |
| Low or unequal pressure (as Rinnai defines it) | Hot about 10–50 kPa, lower than the mains cold | Hot taps noticeably weaker than cold | Rinnai NZ, 1 Sep 2016 |
Figures as published by BRANZ (Building Research Association of New Zealand) and Rinnai New Zealand. They are typical ranges, not a measurement of your home.
Two things jump out of that table. First, the sources don't agree on one number for "low pressure". That's normal: the pressure of a tank-fed system depends on how high the tank sits above the outlet, and BRANZ's figures work out at roughly 10 kPa for every metre of height. Second, the bottom of the low-pressure range is below the 50 kPa minimum our own mixers are rated for. That's why the actual figure at your tap matters more than the label on your cylinder.
Rinnai New Zealand notes that most new homes are built with mains-pressure hot and cold water, while a large number of homes over 20 years old use low-pressure hot water. If your house is more than 20 years old and the cylinder has never been replaced, assume nothing until you've checked.
How to Tell if Your Hot Water Is Low Pressure
Look at the cylinder first, then look up. Many cylinders are labelled, and the roof usually confirms it. These are the checks we'd do before buying any tapware:
- Read the cylinder label. Many say mains pressure or low pressure on the label, often with a pressure rating.
- Check the roof space. A cold water tank sitting above the cylinder is a header tank, and it means low pressure.
- Look at the roof from outside. A thin vent pipe coming up through the roof above the cylinder cupboard is another low-pressure sign. Rinnai treats either a header tank or a vent through the roof as a low-pressure system.
- Run the hot and the cold. If the hot tap runs clearly weaker than the cold at the same basin, you're almost certainly on low or unequal pressure.
- Notice the shower. If it goes cold whenever someone runs a hot tap elsewhere in the house, the hot side is likely the weaker one.
- Ask for a measurement. Your authorised plumber can put a gauge on the hot and cold and tell you the real figures. That's the number to compare with a mixer's rating.
Designer Insight: the cylinder label tells you what the cylinder was designed for, not what reaches your shower. A tank that sits only a little above the bathroom gives a lot less pressure than one high in a two-storey roof. When the decision is between two mixers, get the hot measured at the bathroom, not guessed from the cupboard.
What a Mixer's Working-Pressure Rating Means
A working-pressure rating is the range of supply pressure the manufacturer says the mixer is designed to operate in. Below the minimum, the maker doesn't rate it to work as designed. Above the maximum, the supply needs reducing before it reaches the tap.
Inside the range, "works" doesn't mean "works the same". A mixer's flow rises and falls with the pressure behind it, so the same tap gives a fuller stream on mains pressure than it does near the bottom of its range. Our basin mixers are rated 5 Star WELS at 6.0 L/min, and our showers 3 Star at 8.0 to 8.5 L/min. Those are the tested figures for the WELS rating, and on a low-pressure hot supply you should expect the hot side to deliver less than that.
The rating also says nothing about balance. A mixer can sit comfortably inside its range on the cold side and near the bottom on the hot side, and that mismatch is what you feel in the shower. If you want to know more about the flow figures themselves, our guide to WELS and WaterMark explains the star bands and how WELS labelling works in New Zealand.
How Our Range Is Rated
Every mixer and shower in the table below is rated for a working pressure of 0.5–8 bar (50–800 kPa). That figure comes from the factory technical sheets and installation guides, and it's printed in the specification table on each product page. The pages list the same rating for all six finishes.
Swipe the table sideways to see every column →
| Product | Working pressure | WELS rating | On low-pressure hot water |
|---|---|---|---|
| Vienna Short | 0.5–8 bar (50–800 kPa) | 5 Star · 6.0 L/min | Operates from 50 kPa; expect a softer stream than on mains |
| Vienna Tall | 0.5–8 bar (50–800 kPa) | 5 Star · 6.0 L/min | Operates from 50 kPa; expect a softer stream than on mains |
| Milano Wall Spout Plus Mixer | 0.5–8 bar (50–800 kPa) | 5 Star · 6.0 L/min | Operates from 50 kPa; plan the valve with your plumber before lining |
| Milano Wall Mixer | 0.5–8 bar (50–800 kPa) | No outlet of its own | Flow depends on the shower or spout it feeds |
| Cannes Diverter and Mixer | 0.5–8 bar (50–800 kPa) | No outlet of its own | Shares one blended supply between two outlets, so low pressure is more noticeable |
| Como Kitchen Mixer | 0.5–8 bar (50–800 kPa) | 5 Star · 6.0 L/min | Operates from 50 kPa; sink fills take longer |
| Corsica Dual Shower | 0.5–8 bar (50–800 kPa) | 3 Star · 8.0 L/min | A large rain head on low pressure gives a gentle, wide spray |
| Bordeaux Wall Shower | 0.5–8 bar (50–800 kPa) | 3 Star · 8.0 L/min | As above |
| Lyon Ceiling Shower | 0.5–8 bar (50–800 kPa) | 3 Star · 8.0 L/min | As above |
| Versailles Hand Shower | 0.5–8 bar (50–800 kPa) | 3 Star · 8.5 L/min | Operates from 50 kPa |
Working pressure and WELS ratings as listed on our product pages, 14 Oct 2026, the same in every finish. Not shown: the Porto pull-out kitchen mixer, whose pressure documents we are still confirming with the factory. Ask us about it.
Read the right-hand column as practical experience, not a test result. What we can say for certain is the rated range. What we can't promise is how strong a shower will feel on your particular system, because that depends on the pressure that reaches it.
Here's the honest limit. If your hot water measures under 50 kPa at the bathroom, our mixers and showers are outside their rated range on that supply, and we'd rather you knew before you bought. In that case the better options are either a change to the hot water system or tapware sold specifically for low-pressure supplies.
Unequal Pressure: Why Showers Swing Hot and Cold
A single-lever mixer blends hot and cold in proportion to where you set the lever. It assumes both sides arrive at a similar pressure. When the cold comes straight from the mains and the hot comes from a low-pressure cylinder, the cold side has far more push, so the blend leans cold and any small change upsets it. BRANZ puts it plainly: with low-pressure hot and high-pressure cold, it is difficult to achieve balanced flow to a shower (BRANZ).
That's why the shower goes cold when someone runs the kitchen hot tap: the hot pressure at the shower drops further while the cold stays strong. Rinnai describes the same thing from the other side, people timing their shower around the kitchen tap to avoid a blast of cold water, and notes that modern or imported tapware can disappoint on low or unequal pressure (Rinnai NZ).
A wall mixer with a diverter, like the Cannes, makes this more noticeable, not less, because it sends one blended supply to two outlets. It doesn't fix the imbalance; only the supply can do that. If you're on unequal pressure and planning a rain head plus a hand shower, raise it with your plumber at the planning stage.
Your Options: Decisions for You and Your Plumber
Measure first, then choose. Each of these is a conversation with your authorised plumber, and the right answer depends on the house:
| Your situation | What to discuss | Our tapware? |
|---|---|---|
| Hot and cold both on mains pressure | Nothing special. Check the pressure isn't above 800 kPa | Yes, within its rating |
| Low-pressure hot, measured at 50 kPa or more at the bathroom | Whether the softer flow and the hot-cold imbalance will suit you | Operates within its rating; flow will be lower |
| Low-pressure hot, measured under 50 kPa | Changing the hot water system, or choosing tapware made for low pressure | No, below its rated range |
| Renovating anyway and the cylinder is old | A mains-pressure cylinder, priced before the bathroom tapware is chosen | Yes, once the system is changed |
General guidance. Your plumber's measurement and advice for your home come first.
Upgrading to a mains-pressure cylinder is the change that puts hot and cold on equal footing, and Rinnai New Zealand notes that most new homes are built that way. It's a bigger job than swapping a tap, so price it early. If you're already renovating, the time to decide is before the walls are lined, because it can change the pipework the plumber roughs in.
Choosing low-pressure tapware is the right call if you're keeping a system that measures below our 50 kPa minimum. Some mixers are sold specifically for low and unequal pressure. Check the rated minimum in kPa, not the word "low" in the name.
Keeping what you have is reasonable if your hot water measures inside our range and you're happy with a gentler flow. A basin mixer copes far better than a shower in this situation: you're filling hands, not standing under it. Your plumber may also suggest changes to the system itself; that's their call to make on site.
If the hot water system is part of a bigger renovation, our guide to the order of trades shows where that decision falls.
Common Mistakes
- Buying first and checking the cylinder later. The cylinder label and the roof space take five minutes to check. Do it before you choose.
- Trusting the word "low" or "mains" alone. Compare the measured pressure with the mixer's rated minimum in kPa.
- Expecting a rain head to fix weak hot water. A bigger head spreads the same flow wider. On low pressure it feels gentler, not stronger.
- Judging by the cold tap. On unequal pressure the cold is strong and the hot is weak. It's the hot side that decides how the mixer behaves.
- Leaving the cylinder decision until after tiling. If you might change the hot water system, decide before the plumber roughs in.
- Assuming every finish has the same rating. Ours do, but some ranges rate different finishes differently. Check the exact one you're buying.
Frequently Asked Questions
How do I know if my hot water is low pressure or mains pressure?
Start with the cylinder: many are labelled mains pressure or low pressure. Then look up. A header tank in the roof space, or a vent pipe from the cylinder poking through the roof, means low pressure. A hot tap that runs noticeably weaker than the cold is another sign. If you're still unsure, an authorised plumber can measure the pressure on both sides.
Will a mains-pressure mixer work on low-pressure hot water?
It depends on the actual pressure, not the label. Our mixers and showers are rated for a working pressure of 0.5 to 8 bar (50 to 800 kPa). Above 50 kPa they operate within that rating, but the flow will be lower than on mains pressure. Some low-pressure systems run below 50 kPa, which is under our rated range.
What is unequal pressure?
It's when the hot and cold water reach your taps at different pressures. The usual case is low-pressure hot water from the cylinder with cold water straight from the mains. A single-lever mixer then struggles to hold a steady blend, because the stronger cold side tends to push past the hot.
Why does my shower go cold when someone turns on a tap?
On a low or unequal pressure system, another tap drawing hot water lowers the hot pressure at your shower even further, while the mains cold stays strong. The blend shifts towards cold until the other tap is turned off. Your plumber can tell you whether a change to the system would steady it.
Is it worth upgrading to mains-pressure hot water?
If you're renovating a bathroom in an older home, it's worth asking your plumber about it before you choose tapware. A mains-pressure cylinder puts hot and cold on an equal footing, which suits modern mixers and showers. Whether it's worth the cost depends on your house, cylinder and budget, so get a quote.
Does the finish change a mixer's pressure rating?
Not in our range. The product pages list the same working pressure, 0.5 to 8 bar (50 to 800 kPa), for every one of our six finishes. That isn't true of every brand, so check the specification for the exact finish you're buying.
Designer's Cheat Sheet
Designer's Cheat Sheet
- ✔ Header tank or roof vent? → Low-pressure hot water
- ✔ Hot weaker than cold? → Low or unequal pressure
- ✔ Our rating → 0.5–8 bar (50–800 kPa), all six finishes
- ✔ Low pressure, per BRANZ → about 30–120 kPa
- ✔ Under 50 kPa at the bathroom? → Not our tapware on that supply
- ✔ Before you buy → ask your authorised plumber to measure hot and cold
Conclusion
Low-pressure hot water doesn't rule out a modern mixer, but it does change what you should expect from one. Get the pressure measured, compare it with the rated minimum, and decide whether the system or the tapware is the thing to change. A five-minute look at the cylinder now saves a shower you're disappointed with every morning.
Still choosing? Our shower guide compares rail sets, wall arms and ceiling arms, and the tapware buying guide covers everything else.
Where To Next?
- Related guides: WELS and WaterMark Explained, Wall-Mounted vs Basin Mixers, Bathroom Heights and Rough-In Measurements, How to Clean and Care for Tapware Finishes and Leaking Tap or Weak Flow?
- Mixers: the Vienna Short, Vienna Tall, Milano Wall Mixer and Cannes, or the full Bathroom Mixers & Spouts range
- Showers: the Corsica, Bordeaux and Lyon, or the full Showers & Shower Sets range
Need help? Ask us with a photo.
Send a photo of your cylinder label and the tapware you like, and we will tell you how it is rated, or email info@invoguemirrors.co.nz.
