Frequently Asked Questions for Rezi Instantaneous Water Heaters

Rezi FAQs


Why buy a Rezi water heater?


Primarily, your Rezi water heater will save you money in several ways:


For a start, it is probably the lowest priced device of its type available in Australia, beautifully designed and manufactured in Europe, complete with a genuine two year warranty.  They are popular throughout Europe, having won many awards. Thousands of Rezi water heaters have been sold in Australia over the past nine years.


Your Rezi will save you




SPACE and even



1    The Rezi is tiny, designed to be installed close to your water outlet. You save the TIME it takes for hot water to arrive at the tap.

2        The Rezi heats water only when the hot tap is turned on. You save POWER because you heat only what you use.  There is no storage or wastage of heated water cooling off in long pipe runs.

3        You save WATER because you don’t watch water running down the sink while you wait for hot water to arrive.

4        If you already have your own tap fittings the Rezi can be mounted “in-line” under the sink or basin.  You will save SPACE by installing your Rezi at any convenient angle – vertical, horizontal, upside down – whatever makes sense.

5        Mounted above the sink, the Rezi comes complete with its own MIXER TAPS and SWIVEL SPOUT so depending on your situation, you may not need to purchase expensive fittings.



Which Rezi for me?


Presently we offer four 240V (single phase) and three 415V (three phase) models. 

The model you choose will depend upon the power (in Amps) that you provide and will affect the volume of hot water you can achieve.


240V Single Phase Models


Rezi 3.3kW has been specifically designed for caravanners. It draws 13.75 Amps @ 240V and produces 2.1litres of hot water per minute (lpm).  Typically caravan parks provide 15 Amps to each site so the Rezi 3.3 won’t brown out the neighborhood!


Rezi 4kW is ideal for under the kitchen sink. It draws 16.7 Amps @ 240V and produces 2.3 lpm.


Rezi 5kW is great for general household use.  It draws 20.8 Amps @ 240V and will provide 3.0 lpm.


Rezi 7.3kW is our latest model drawing 30 Amps @240 and providing 4.5 lpm. 

415V two(2) Phases plus Earth Models. 


Rezi 7.5Kw, 9kW and 11kW all require 415V connection and must be installed by a qualified electrician.  415V can kill!  Although 415V is generally referred to as three phase, these models use two of three phases plus earth.


Rezi 7.5kW draws 18 Amps per phase and provides approx. 4.5 lpm.


Rezi 9kW draws 21.7 Amps per phase and provides approx. 5.5 lpm.


Rezi 11kW draws 26.5 Amps per phase and provides approx. 6.5 lpm



How hot is “Hot Water”?


All Rezi water heaters look and operate the same way.  Cold water is passed across heating elements which add approximately 25C degrees to the ambient (incoming) temperature. The higher the power of the unit, the more hot water is produced.  Water temperature remains constant across all models.  Hot water volumes quoted above are all based on 40C (ambient 15C + 25C).  Ambient temperature will obviously vary across Australia depending upon where you are and the time of year.


Rezi heaters can produce water at higher temperatures, up to 55C, by reducing the water flow at the hot water tap or mixer. A lower flow rate gives the element more time to heat the water.



Can I have a Shower?


Sure can, provided your expectations are within the water flow constraints given above.

All Rezi models will usually need cold water added to give a comfortable shower.  You will need a water-reducing shower head to get a reasonable shower effect. Don’t expect Niagra Falls! We can provide an inexpensive but efficient shower Rezi accessory if required.


The following questions have been asked of us via email recently: 

"Need to replace an old electric storage heater in a holiday home. Has 2 showers and two kitchens. What do you suggest? ".

All 240V Rezi heaters are the same price, the only difference between models is the power you are prepared to provide.

A typical installation such as you have described is to install an undersink Rezi feeding both the kitchen and the bathroom.  A Rezi 4kW unit "inline" for each kitchen would be a good solution.  This draws about 17 Amps but in most circumstances will work well off a standard 240V GPO. In most situations, electrical wiring will handle 22 Amps.  If in doubt, consult your electrician.

Provided that kitchen and bathroom shower is not used concurrently this will work fine, provided that you have a water limiting shower head installed.  If you need shower head, we offer the Wh/S shower that has been designed for the Rezi at a reasonable price.

If you are interested, go to our website and click on the Rezi link.

Order 2 X Rezi 4kW with T-Piece.
If you want the shower head, include 2 X Wh/S Complete showers

The Rezi 4kW provides 2.3LPM.

Bear in mind that instantaneoous heaters function differently to storage heaters. When using the shower, our advice is to turn the hot tap on full and then temper with cold water.  To increase the water temperature (up to 55C) simply reduce the hot water flow slightly.

"I am after a replacement electric shower head and a under sink heater at our shack, would a Rezi do this if so can u send me some model numbers and prices?"

We can offer a variety of Rezi heaters, all the same price but varying in their power consumption and hot water volumes.

The Rezi 3.3kW unit produces 2.1 Lpm and draws 13.75 Amps
The Rezi 4.0kW unit produces 2.4 Lpm and draws 16.67 Amps
The Rezi 5.0kW unit produces 3.0 Lpm and draws 20.83Amps

All of the above will produce a reasonable shower volume, provided that you have a water saving shower head. The Rezi Wh/S shower head is reasonably priced and has been designed to work efficiently with the Rezi heater.  In addition to limiting the input water volume it also mixes the hot and cold water nicely for optimum temperature control.

When you install you Rezi heater "in-line" you will need to order the Rezi T-piece as well , which is an additional $38.00 + GST.

Thanks for your enquiry.


See the following queries - answers are in bold...

We have an instantaneous gas hot water system which takes a long time to provide hot water to the kitchen – thus water is wasted while we wait, which is particularly galling as we rely on rain tank water. The Rezi is tiny and can be installed close to your sink taps at any angle.  Just be sure that the water flow follws the arrows on the back of the Rezi as it won't work if the water flows the wrong way. Install Rezi upside down if necessary to comply with the water flow direction.

We are looking for a booster system that can be plumed into the existing hot water line and will heat the (cold) water instanteously until the hot water from the gas heater arrives.  Ideally the booster would then cut out.  This is impractical (and unnecessary) as the Rezi will add  25 degrees +  to the ambient temperature to a maximum of 55 C.  It has no thermostat so you will be wasting gas energy for no good result.  The Rezi will also restrict the water flow somewhat as it is designed to bring the water temperature to specification by limiting the water throughput.

Is the Rezi the answer?  Yes  Or will the Rezi add 25 degrees to the hot water from the gas heater?? It will add 25c + until the temperature gets to 55C.  It cannot add greater heat than this and will not cut out, thus, the Rezi will be costing you electricity for no benefit once the gas heated water arrives.  Typically, by the time this happens, you will have turned the hot tap off and you will have heated all the water in the line for nothing!

To achieve higher temperatures, slightly reduce the hot water flow at the tap to give max temp of 55C.


Useful steps:

1.  Buy the Rezi with Rezi  T-piece that best meets your power availability - 

240 Volt models 3.3kw uses 14 Amps, 4kW uses 17 Amps, 5kW uses 21 Amps. 

Check this with your electrician.  

They are all the same price, the more power you provide, the greater volume of hot water you get. (2.1 lpm, 2.4 lpm, 3.0 lpm respectively).  All of these models are  fine your application. 

Please refer to the performance table on our website  If you have 415 Volts available, great, but definitely check with your electrician!

2.  Cap the hot water inlet under the sink (from your gas HWS) and forget it - never use it again for the kitchen sink.

3.  Buy a standard 1/2" T-piece from your hardware store and install it on the cold water inlet - one side to the cold water mixer tap and the other to the Rezi dual T-Piece which connects to the body of the Rezi.  Connect the hot water side of the Rezi T-piece line to your mixer hot tap.  Use plenty of white plumber's tape.

4.  Job done.


"Live top end of S.A, however wish to mount in a caravan, under the sink to do both sink and a shower, at the other end of the Van, all on 240V mains power, any suggestions?"

We recommend the Rezi 3.3kW for caravanners as it draws less than the 15 Amps usually provided  at van parks. The Rezi dual T-piece is installed in line under the sink and mounts the Rezi heater body. 
You will need a couple of standard 1/2" t-pieces from the hardware store to direct the incoming cold water to both cold tap over the sink and to the Rezi T-piece together with a 10Amp or 15 Amp electric plug.  (We have found that a 10Amp plug will handle the load adequately when used for the purposes you describe).
Fit another t-piece to the hot water end of the Rezi t-piece to direct hot water to the sink and to the shower.  USE PLENTY WHITE PLUMBER'S TAPE when connecting the brass t-pieces.
In order to achieve a satisfactory shower, you will need a water conserving shower head.  We recommend the Rezi Wh/S Complete shower unit as it mixes the hot and cold water well and provides a reasonable shower at a reduced water rate.
To order, go to, click on the Rezi picture to proceed.
Select the Rezi 3 with T-piece ($276 +GST) and also select the Wh/S Shower set.
Useful info:
Rezi water heaters provide an ideal low cost solution to your under sink applications.

Rezi has an Australian Electrical Safety Certificate.  We do not have the Australian Watermark certificate nor do we intend to do so.

Rezi water heaters has been installed in thousands of sites in Australia over the past several years.  A two year return to base warranty is provided.

If you wish to place an order via our website (, choose the unit that meets your power availability and order the T-piece option for under the sink installation.

All pricing is similar, $238 + $38 (t-Piece) + $20 freight + GST.

We usually recommend the Rezi 4kW for dishwashing. This model will provide 2.4 lpm approx and draws 17 amps. If you have the power available, the Rezi 5kW offers
3 lpm and draws 21 amps.


Any more questions?   

If you are unsure on any matter, please email to [email protected] so we can add your question and our response to this list.


Thanks for reading!

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