Greenvision Energy

Dimplex Quantum Smart Water Cylinder

Hot Water Cylinder Guide

We have compiled a wide range of information about hot water cylinders to hopefully answer all your questions. Including things you should consider before installing a hot water cylinder and frequently asked questions.

In the average home, the hot water heater is responsible for about 17 percent of the total energy use, according to the Department of Energy.

Why upgrade your old water cylinder to a pressured unvented water cylinder?

There are many reasons to think about upgrading your boiler/water cylinder. Constant leaks or breakdowns could mean that it’s time to think about replacing instead of repairing, as this will save you money in the long run. A new boiler will be much more energy efficient and could pay for itself quite quickly. A new professionally fitted boiler will be sized correctly to meet the needs of your family and space available.

An old cylinder with a red jacket will mean higher energy bills. Upgrading to a new cylinder and better tariff would make your heating more efficient and cost effective. An off peak tariff in conjunction with the two element cylinder could save you lots of money.

If water pressure is low and it takes forever to run a bath or the shower is just a dribble, a new unvented hot water cylinder will give amazing improvements.

If, however, you are considering a larger cylinder, it is vital to make sure you have sufficient space in the existing location to comfortably fit the new cylinder. Most airing cupboards are built around the size of the cylinder when the house is built, which means that a larger cylinder may not fit in the current space.

What are the different types of electric heaters?

Dimplex Water Cylinders

Unvented hot water cylinders

These were only made legal in the UK in 1986, but have since grown rapidly in popularity. In an unvented system there is no cold water tank, instead, the sealed hot water cylinder is fed directly by the cold water mains. Since they are operating at mains pressure, they offer much better flow rates, meaning your shower and bath performance should be higher.

The other major benefit is that you don’t need to maintain a cold water tank in the loft (which vented systems require). This is good news since not only does it free up space, it also removes the potential freezing issue during our long cold winter periods.

In addition, an unvented cylinder can be located pretty much anywhere in your home as there is no reliance on gravity to move the hot water around.

Vented Cylinder

Vented hot water cylinders

Vented hot water tanks remain the most common type of hot water system found in the UK. Unlike newer unvented tanks, these copper tanks are fed by cold water from a header tank (normally located in the loft) and use gravity to drive the hot water around the home. Cold water in the header tank is linked to the vented hot water cylinder through a vent pipe.

The hot water pressure tends to be governed by the height of the water tank above the tap or shower feed which means that, although the pressure might be excellent on the ground floor of the home, in rooms on upper floors the pressure will be lower.

As a result, many showers in homes with vented hot water tanks use electric pumps to drive the hot water to the shower at increased pressure. Vented hot water cylinders are far less complicated than the pressurised unvented systems so they are much simpler to maintain and install. This makes them a far cheaper option when compared to the unvented system.

What is an Indirect System​

Most hot water cylinders are heated via an external heat source such as a gas boiler or solar thermal panels. This means that hot water is heated and fed through a copper coil in the hot water tank. Heat is then transferred from the external heat source to the water inside the hot water tank.

Indirect cylinders tend to be fitted with a direct backup (such as an immersion heater). Even if the boiler is broken, you can still produce hot water as and when you need it. Indirect systems can be either vented and unvented.

What is a Direct Systems

In a direct cylinder system, the hot water is heated directly by an internal element such as an immersion heater which can make the hot water more expensive to produce. Some homes have no access to gas, for example a mid-level flat, so they are forced to go with a direct system for their hot water. In such cases it is advantageous to choose Economy 7, which will give cheaper electricity at night to heat the hot water.

Normally this type of cylinder would be fitted with two different immersion heaters, one for peak and one for off-peak electricity. If this is the case, it is important to make sure that the immersion heaters are set up on the timers correctly to ensure you are paying the least possible for the hot water. 

Herschel Select Mirror Infrared Panel Heater

What are benefits of an unvented water cylinder?

Unvented cylinders take up less space in your property because they don’t require a feeder tank in the loft. They also tend to provide stronger water pressure than an open vented system. This is because unvented cylinders are directly supplied via the mains and because they don’t rely on gravity to function, they can be installed almost anywhere in your home, which makes it easier to install in a place more suitable for you.

There are also horizontal cylinders available for loft spaces.

Pressurised hot-water cylinders give Invigorating showers and baths can be filled much more quickly.  They also allow you to be in control of your water temperatures to exact degrees.

How do unvented water cylinders work?

An unvented system has no cold water tank, instead it’s a sealed hot water cylinder which is fed directly by the cold water mains. An unvented cylinder is kept pressurised from the incoming water supply and is heated by either an immersion heater (a direct model) or by an external heat source such as a boiler or wet solar system (an indirect model).

An unvented cylinder will have pipework connected to it that distributes the hot water to multiple outlets around the house. As soon as a tap or shower is used, the pressure of the incoming cold water drives the hot water in the cylinder towards the open outlet at mains pressure.

Unvented systems are ‘sealed’, so they use an expansion vessel to allow for the expansion of water in the system as it heats up. The expansion vessel is sited either next to or within the boiler or cylinder and can accommodate the increase in pressure by up to 4.5 bar.

Unvented cylinders are designed to withstand considerable internal forces and are extremely safe to use when fitted with all the correct pressure equipment. They are usually made from stainless steel due to the high tensile strength that can be achieved from a fairly thin sheet.

Woman in hot bath

Things I should consider before installing a hot water cylinder.

1) What type of cylinder should I install?

Think about your type of property and your requirements e.g. if you are in a mid floor flat with no loft access and your cylinder is positioned in the centre of your flat it may be difficult to install an unvented cylinder. A thermal store may be a better option as there is no need for additional pipework. Greenvision can advise on this.

2) Size of the water cylinder.

If you only have one bathroom, with just an electric shower you will only need a small cylinder or undersink heater that heats water at the point of use.

3) Location.

You might be able to free up valuable space by moving the cylinder into the loft or garage. If your cylinder is located in your bathroom and you are planning to remodel your bathroom it could be a good time to plan ahead.

4) Usage.

If you are using a shower running off your water cylinder, you need to bear in mind that a  pressurised water cylinder can use up to 8-12 litres of water per minute. So a 120L cylinder can be drained very quickly.

5 ) Number of bathrooms.

If the water cylinder is serving two bathrooms, it may be better to install an electric shower in, say, the ensuite.

6) Number of heating elements fitted to the cylinder.

If you have economy 7 it would be a good idea to connect one of the heating elements to your low rate tariff at night.

7) What type of company should I get to install my Unvented cylinder?

As with any major changes to your home it is vital to do plenty of research and talk to the experts about your requirements.  Always make sure you know what you want to get out of your new system to benefit your home, to be more efficient and cost effective and of course make sure you have a budget in mind.  A reputable company will be able to offer advice on the best option for your needs and budget.

Frequently asked questions about hot water cylinders

A pressure reducing valve is placed on the incoming cold water mains pipe linked to the hot water system and is designed to reduce the water pressure slightly and keep it at a constant level.

A line strainer is fitted on the incoming cold water mains pipe and is used to filter out any particles that might come from the cold water system. Due to the sensitive nature of some of the components even a small piece of grit could cause them to malfunction. The strainer keeps them clear.

The expansion vessel deals with the expansion of the water in the system as it is heated. As water gets warmer it expands, by up to 4% in volume and it has to go somewhere. The expansion vessel is designed to store this extra water and stop parts of the system bursting.

This valve is also part of the ‘sealed’ heating system. It is designed to remove pressure from the system.

A Tundish is connected to the pipe coming from the relief valve. It is a device which is placed in the pipeline to alert you to any faults in the system, as you will be able to see the water flowing out of the safety valve(s).

Greenvision water cylinder warranties are for 15 years

Couple stood in kitchen looking at brochure

What people think

Based on 33 reviews
Isobel Gleave
Isobel Gleave
I'm very pleased that I went ahead and replaced my old storage heaters with the new Dimplex ones. The whole process went smoothly and efficiently and Greenvision were very helpful at all stages and didn't rush me. Apart from working better than the old ones they also look smart, as does the new bedroom panel heaters. The installers did a brilliant job and didn't leave a trace.
Gemma Rogers
Gemma Rogers
Quality service for installation of a new Dimplex Quantum storage heater, Rointe electric towel rail, updated fuse box and all associated. The service provided by Greenvision went beyond all expectations. Everyone was extremely helpful and friendly. Stuart and Paul provided professional advice based on what would be best for me. The virtual survey option was ideal, so we could discuss options and get a quote straight away, which meant from contacting Greenvision to installation was only a couple of weeks! Amanda was great in keeping me up to date about the installation and arrangements. On the day, Dan arrived exactly when expected and fitted everything perfectly, it's made such a difference. Thank you to everyone at Greenvision. Very impressed and wouldn't hesitate to recommend!
Peter Graystone
Peter Graystone
I found Greenvision very pleasant to work with. The explanation of the product, and the survey to check it was suitable for my home were both excellent. The engineer was courteous and efficient, although I would have loved it if he had vacuumed before he left. I'm very pleased on the whole.
Purchase and installation of Dimplex Quantum Storage Heaters. Very professional from start to finish. In contact throughout. Answered questions and were friendly and helpful. Fitters were very efficient and even brought a hoover to clear up afterwards! They explained everything regarding usage. Very polite and professional from start to finish. Would recommend.
ann munro
ann munro
I instigated my business with Greenvision 6 weeks or so ago. The staff at Greenvision were informative, considerate of my needs and quick to answer any queries. Adjustments to my advantage were made after a survey which have proved to be most adequate. The installation occurred on 16th. January. The engineers were on time, efficient and considerate, clearing up and tidying up as they proceeded. They took time to make sure I understood the basics of operating my heaters. I will certainly recommend Greenvision where and when I can. So quick.
Sarah Moyer
Sarah Moyer
I used Greenvision for purchase and installation of 2 electrical high heat retention heaters for use with Economy 7. Everyone at Greenvision was friendly and helpful. Although based in Nottingham they facilitated installers for me in London. The whole process was seamless, quick and efficient. I would certainly recommend this company.
Carol G
Carol G
We purchased new Dimplex storage heaters through Greenvision. I was totally impressed by their level of knowledge, advice, customer service and ability to organise an efficient installation of these products at our property in North Wales. Highly recommended!
Lucy Reynolds
Lucy Reynolds
Very pleased with the installation of a Quantum Dimplex storage heater. Clearly explained at all stages and electrician who installed it was excellent.
Ray W
Ray W
6 Dimplex Quantum storage heaters installed to replace old heaters and associated modifications carried out to wiring in meter cupboard. Friendly helpful installers and very professional job. Highly recommended.
Brian Lomas
Brian Lomas
Supplied and fitted 3 Dimplex Quantum storage heaters. Used Greenvision because other residents in our retirement flats recommended them from their experience. They were right to do so as our experience was the same. From start to finish our experience was seamless and efficient ,polite, friendly are words that come to mind. The team that arrived with us on installation day was Nathan/Paul and Luker. All three were cleanly dressed, polite and friendly but courteous. They were very competent indeed and represented an excellent image of the Company. J B and L Lomas SANDBACH

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Electric Water Cylinder