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Explaining electric hot water heaters

What is an electric hot water heater?

How do electric hot water heaters work?

What are the differences between hot water heaters available?

Most of us don’t give a passing thought to how our water is heated as long as it is hot when we turn on the hot water tap or get in the shower. There are various ways our water can be heated and these generally are by Gas, Heat Pump, Solar, Wetback or Power (Electricity).

An electric powered water heater can be referred to by many names – a hot water storage tank, a hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank or a hot water cylinder.

storage_hot_water_heater

Electric hot water cylinders are the most common form of water heating in New Zealand.

The cylinders use an electric element in an insulated tank to heat the water to a temperature set by a thermostat.

It acts a bit like a hot water jug or kettle. It has an immersion element inside the cylinder (which looks like a metal loop or coil) and it heats the surrounding water.

The cylinder is an insulated water tank with a cold tube to carry water in, and a hot tube to send the water where it’s needed inside the home. The heating is controlled by a thermostat that turns on the heating element when the water goes beneath the pre-set temperature.

When the heating element is on, electric power runs through it, creating heat. Unlike a gas water heater, the heat does not go through a heat exchanger. Instead, it flows directly into the tank’s water supply.

Electric water heaters (with an immersion element) are more energy efficient than gas water heaters. A conventional electric model averages a 90 percent efficiency rating, while a conventional gas water heater averages a 60 percent rating. Electric power is generally more expensive than natural gas.

Gas does outperform the electric model in water heating speed and recovery time. A gas heater can heat around 190 litres in roughly an hour, while an electric heater takes several hours to heat the same volume.

Some other benefits to electric hot water heaters are that out of all the various types of water heating products available, they have the lowest upfront cost.

They also have a certain amount of flexibility. You can buy cylinders with additional connections suitable for having a solar water heater, heat pump water heater or wetback added in the future. This allows you to change the way you use your hot water, and for adaptation should your family size grow or the demands you require on hot water change.

You can purchase an electric hot water heater that has a thermostatic control. This means that it will automatically turn off when it reaches the temperature you set on the thermostat. This will save you money over time.

If you have a boiler system in your home, an electric water heater will not be connected to your boiler. This means that if your boiler breaks down, you can still generate hot water for your home.

If you well insulate your electric water heater, it can keep water hot for several hours after it switches off. You can set a timer on your heater so that it only switches on during cheaper off-peak electricity hours.

You can usually turn your electric water heater on or off by simply flicking the switch on the wall socket. This is a great power savings ability especially useful if you are going away on holiday and you will have no need for hot water in the house while you are away.

And what kind of things should you be aware of regarding an electric hot water heater?

  • Heating water using electricity is more expensive than heating water with say, gas. A typical electric water heater uses 3 kilowatts of electricity an hour, so it will cost the average house about 78c an hour to run. Most households will need to run an electric water heater for at least a couple of hours a day to get the water hot enough – costing at least $560 a year.
  • An electric water heater needs a thermostatic control, otherwise it can heat the water to far too high a temperature.
  • Some heating engineers may recommend you leave your electric water heater on 24/7 – however, this can be very expensive unless it has a thermostatic control.
  • Be aware that you need to heat the water in your electric water heater to above 50°C to kill off bacteria.Above all consider all of your options. What works for one household might not be the best option for yours. Getting the sizing, the placement and the installation right is important for obtaining your long term enjoyment from your new water heater.
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Rinnai is getting greener in 2017

Rinnai have been busy with some exciting changes to products making sure they remain one of New Zealand’s preferred suppliers of electric hot water cylinders. The next 12 months will see some exciting changes to their range starting with changes to some of the Mains Pressure Enamel products.

Always striving to be at the forefront of future-proof technology, Rinnai, as part of our commitment to the environment has made changes to our manufacturing process. Innovations to the materials that we use to assemble our finished products will enable our cylinders to be kinder to the environment while still allowing us to meet the same exacting standards you have come to expect.

These changes will mean that the height of some of our Mains Pressure Enamel Electric cylinders will be changing over the coming months.

The first of these changes will be reflected with the production of our Mains Pressure Enamel 180L 488 product (ME18048830/ME18048820). This means that all orders from now on will be fulfilled with the new height.

The full schedule of changes to affected Mains Pressure Enamel cylinders can be found below:

CODE LITRES DIAMETER EXISTING HEIGHT NEW HEIGHT KW CHANGE WINDOW
ME18048830 180 488 1660 1695 3 NOW
ME18048820 180 488 1660 1695 2 NOW
ME25059030 250 590 1580 1595 3 MID NOV 2016
ME25059020 250 590 1580 1595 2 MID NOV 2016
ME250590D30 250 590 1580 1595 2X3 MID NOV 2016
ME250590D20 250 590 1580 1595 2X2 MID NOV 2016
ME18059030 180 590 1190 1205 3 END NOV 2016
ME18059020 180 590 1190 1205 2 END NOV 2016
ME09048830 90 488 955 1030 3 EST MAR 2017
ME09048820 90 488 995 1030 2 EST MAR 2017
ME13548830 135 488 1295 1328 3 EST JAN 2017
ME13548820 135 488 1295 1328 2 EST JAN 2017
ME30059030 300 590 1790 1805 3 JUN 2017
ME30059020 300 590 1790 1805 2 JUN 2017
ME300590D30 300 590 1790 1805 2X2 JUN 2017
ME300590D20 300 590 1790 1805 2X3 JUN 2017

From November 2016 we will be phasing out the dual element 2kW and 3 kW 180L Mains Pressure Enamel products (ME180590D30 and ME180590D20) from our range. Stocks of this product will not be replenished and orders for these products will continue to be fulfilled while stocks last.

As always, Rinnai is committed to the environment and to our customers. For more information on any of the products discussed above please contact us 0800 4 CYLINDERS

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Blowing up a hot water cylinder

I made this GIF from an experiment done by Myth Busters to show the extent of damage a hot water cylinder can do when there is no pressure relief. blowing-up-hwc

The image above reinforces the importance of using individuals that understand the physics of hot water and the effects an installation can have on its surroundings.

So at what point will a cylinder explode?

In principal it’s simple to understand. Heating a substance causes molecules to speed up and spread slightly further apart, occupying a larger volume that results in a decrease in density. So “larger volume” means “more space” which is limited to the size of the hot water cylinder.

If hot water is not used and your thermostat fails, your immersion element will continue heating your water (to boiling point) until such time one of the pressure relief valves activates and relieves the pressure. Every installation should include two relief valves, one on the cold water side and one on the hot water side.

This regulation was put in place around 1997 meaning that any cylinders installed prior to that may only have one source of pressure relief. Hence the low pressure vent copper pipe going through the roof.

This is where it gets tricky. Many installers dont bother replacing older valves when replacing an old hot water cylinder with a new one. Others have managed to install a tempering valve on a low pressure system right into the overflow pipe, blocking the only means of pressure relief. The hot water system then becomes a time bomb which may result in something pictured above.

Sometimes its not the plumbers’ fault but rather the homeowner who sees a pipe dripping on the outside of a house and thinks.. “Oh, this should not be leaking” and decides to “blank” it off by any means available, creating the perfect conditions for a catastrophe. My recommendation on this is, see a dripping pipe? Please call the plumber.

If you are unsure about what valves you need or already have, send us an email or give us a call for help.