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Hot Water Cylinders: How to Choose the Right Cylinder for your Home

Different Types of Water Heating:

This article is about choosing the correct hot water cylinder for your home, but before we go into the details of this, it's usually a good idea to understand the different ways of getting hot water out of a tap.

On-Demand Water Heating from a Combi Boiler:

You can get on-demand hot water from your central heating boiler if you're using a Combination or Combi Boiler (as they are more commonly known).

These boilers only heat water when a tap or shower is switched on and there is a demand for hot water.

Stored Hot Water in a Cylinder:

The other alternative is to use a Hot Water Cylinder to store and heat water. These can heat the water using a system or open vent boiler, a renewable source of energy such as an Air or Ground Source Heat Pump, or by using an electric element.

This article aims to help you decide which type of cylinder to buy if you believe this type of hot water source is your best option.

Which Should I Choose?

Combination boilers are fantastic machines, but you should keep in mind that they've been designed to operate under certain circumstances. If you fall into these then a combi boiler will be absolutely perfect for you. Trouble starts when people install a new combi boiler without first making sure that they can cope with the many limitations.

Combi boilers can provide both instant hot water and central heating, but not at the same time. They are set to prioritise hot water over central heating, so when hot water is being run there is no output to the central heating system. You can see the problem here if someone wanted to run a hot bath in the middle of winter!

If several different taps are switched on at the same time, the water pressure at each tap will be greatly reduced. If someone is downstairs doing the washing up at the same time you're trying to run a bath, you could be in for a very long wait.

If you live in an area with particularly severe winters, a combi boiler may not be your best choice either. Both the efficiency and the water temperature from a combi suffer in winter as the water flowing through the pipes cools more rapidly, and more energy than usual is required to push water around the home.

Because the distance from heat source to tap can vary dramatically with a combi, depending on your mains water pressure you may have to wait for up to a full minute for the hot water flow to reach the furthest taps.

Combi boilers are most suited to homes with low hot water demand such as one-person apartments, holiday homes (where the heating is only used when the home is occupied) and bungalows.

Houses with multiple bathrooms, large families or even small families with teenagers, where the bathroom is a hive of activity in the mornings and at especially at weekends, would almost certainly be better off with a hot water cylinder supplying their needs.

Different Types of Hot Water Cylinder:

Once you've decided that a stored hot water solution is your best option for providing hot water, you need to understand the different types of water cylinder on the market.

Traditional Hot Water Cylinders:

In a traditional cylinder the water is fed to the cylinder from a cold-water storage tank, known as a header tank, situated above the cylinder. The force of gravity is harnessed to generate the pressure that pushes water down from the tank into the cylinder; the higher above the cylinder the header tank is, the greater the water pressure.

The greatest advantage of such a cylinder is that due to the distance between header tank and cylinder, you will receive an improved head and thus a better flow of water at the taps than with a combination cylinder.

Combination Hot Water Cylinders:

If you don't have access to a loft or other roof space to install a header tank, you might want to look at a combination cylinder. Specially designed for homes with limited roof space, what would have been the header tank has been incorporated into the upper body of the cylinder. As it now comprises of both the header tank and a water storage unit, this is known as a combination cylinder.

The main advantage of a combination cylinder is convenience. It requires far less space than a traditional header tank and cylinder installation; however as the header tank is far closer to the cylinder, the water pressure will not be as high as with a traditional setup.

Different Types of Hot Water Systems:

Now that you've decided on the type of cylinder you need, it's time to take a look at how that cylinder will fit in with your existing central heating system. There are two types of hot water systems, namely open vented and unvented.

Open Vented Hot Water System:

Traditional hot water storage systems consist of a header tank positioned above the cylinder, usually in the loft, which contains a large volume of cold water. These systems are powered by gravity, relying on the weight of the water in the storage tank and the distance between the tank and the cylinder to push water down the pipe which leads to the hot water cylinder.

A vent pipe leading from the cylinder to the outside of the house allows excess pressure to escape and in the event of overheating, a secondary pipe runs from the top of the cylinder back up to an open vent just above the water level in the header tank.

Here are the advantages of an open vented hot water cylinder system:

• Can be installed by a regular plumber or keen DIY'er
• Simple and relatively inexpensive to maintain
• Gives the option of a traditional airing cupboard
• Gives the option of installing a power shower
• Less expensive than unvented cylinders

And here are the disadvantages of an open vented hot water cylinder system:

• Available hot water is limited by the size of cylinder and the recovery time
• Large amount of space required for tanks, cylinders and pipe-work
• Possibility of low or unbalanced water pressure at taps and showers

Unvented Hot Water System:

In an unvented hot water system water is stored at mains pressure where it can be distributed throughout your home. To maintain this pressure, the entire system must be completely sealed and self-contained; meaning a method other than a vent pipe must be used to relieve excess pressure.

Cold water is fed through a pressurised tank inside which it is heated by the cylinder's heat source, either directly or indirectly. Hot water stored inside this tank is then forced out into the cylinder by the incoming cold water at mains pressure, where it can be drawn off whenever a tap is switched on.

To allow water inside the cylinder to expand as it heats up, a closed container known as an expansion vessel is used. A flexible rubber diaphragm separates the pressurised air inside the vessel from the expanding water outside. This pressurised air acts as a cushion against the impact of the rapidly expanding water, allowing pressure waves to dissipate harmlessly while keeping water out of the vessel.

Just like an open vented cylinder, an unvented water cylinder also has a number of advantages and disadvantages.The advantages are:

• High water pressure ideal for showers
• Balanced water pressure at both hot and cold taps
• Balanced shower pressure
• No need for a cold water storage cistern in the loft
• Quicker and easier to install than an open vented cylinder
• Installation and maintenance will be carried out by a qualified professional to local safety regulations

And the disadvantages are:

• Controls need more space than those of a traditional open vented system
• Unvented cylinders are usually more expensive than open vent cylinders

Different Styles of Hot Water Cylinder:

Hot water cylinders come in a variety of styles, each best suited to homes with differing energy needs and hot water systems.

Direct Hot Water Cylinder:

In a direct cylinder, the water is heated via a heat source located within the cylinder, such as an electrical immersion heater. Cold water is fed into the bottom of the cylinder and the heat coming from the heat source rises up to the top of the cylinder where it heats the water which is then drawn off and used for drinking and bathing.

As this heat source is heating the water ‘directly' without relying on an external source such as a boiler, this type of cylinder is known as a direct cylinder.

Indirect Hot Water Cylinder:

With an indirect cylinder, a pipe carrying hot water from your boiler feeds through the cylinder, heating up the water around it as it goes. The section of pipe that goes through the cylinder is shaped like a coil, so that as much of the pipe remains in contact with the water as possible to maximise heat transfer.

Since the main heat source for the water in the cylinder is not located within the cylinder but comes from an external source, this type of cylinder is known as indirect.

Twin Coil Hot Water Cylinder:

If you have an old back burner or a wood-burning stove as well as your central heating boiler, a twin coil cylinder will allow you to connect that heat source to the cylinder as well.

This doubles up on the amount of coil inside that can transfer heat to the water in the cylinder and thus increases the speed the water is heated at.

Solar Hot Water Cylinder:

Solar systems incorporate both solar collecting panels and a sealed control kit with safety valves.

The panels absorb the sun's energy in the form of light, and channel that energy through the system to the single coil in the cylinder, providing an energy source to heat the water inside.

Different Sizes of Hot Water Cylinder:

The next thing you'll need to think about is what size and volume of hot water cylinder would best meet the needs of you and your family.

In modern homes hot water usage has been calculated to range between 35 and 45 litres per person per day; therefore you might think that a 200 litre cylinder will store more than enough hot water to supply the average 4 person family for a full day.

However this doesn't take into consideration that some members of the household may take longer in the bathroom than others, may prefer power showers over standard, may leave the tap running while brushing their teeth or that a family may use a dishwasher instead of doing the washing up.

Teenagers in particular are notorious for using more than their fair share of water, and the simple act of taking a bath can more than double your daily water usage.

This makes it important that rather than choosing a cylinder which turns out to be too small for your needs that you choose a larger cylinder than you might at first think would be necessary. It's always better to have a cylinder larger than you need, than to have one that's too small and only find out after it's been fully installed!

The following table gives the sizes and capacities of standard hot water cylinders that can be installed in the UK:

Standard Cylinders

British
Standard
Type Ref

External Diameter
(excluding foam
insulation)

External Height
over Dome

Min Storage Capacity

 

Direct Indirect mm mm Litres Litres 0 300 1600 98 96 1 350 900 74 72 2 400 900 98 96 3 400 1050 116 114 4 450 675 86 84 5 450 750 98 95 6 450 825 109 106 7 450 900 120 117 8 450 1050 144 140 9 450 1200 166 162 9e 450 1500 210 206 10 500 1200 200 190 11 500 1500 255 245 12 600 1200 290 280 13 600 1500 370 360 14 600 1800 450 440

You've probably spotted that indirect cylinders have a slightly smaller storage capacity than direct; this difference is a result of the space inside the cylinder that has to be taken up with the heating coil instead of water.

Different Grades of Hot Water Cylinder:

When looking into Hot Water Cylinders you might come across the term ‘grade' and wonder what it means.

A cylinder's grade gives the maximum distance above the cylinder the header tank can be, and thus the maximum water pressure the cylinder can withstand.

There are three different grades of cylinder:

• Grade 1 can withstand up to a 25 meter head of water
• Grade 2 can withstand up to a 15 meter head of water
• Grade 3 can withstand a up to 10 meter head of water

The average household hot water cylinder is made to Grade 3 specifications, meaning your header tank can be safely positioned anywhere up to 10 meters above the cylinder.

Insulation of Hot Water Cylinders:

Much more than just an afterthought, proper insulation or lagging is absolutely essential on a hot water cylinder. It's completely ridiculous to heat a large volume of water only to let it go cold again. Would you boil a kettle and then let it go cold before pouring a cup of tea?

Many older properties may have an unlagged cylinder, but their owners might as well be burning money for every second the cylinder is on. It's a blessing in disguise when one of these finally fails, as the replacement cylinder will invariably arrive lagged and go on to show how much more efficient it is.

Modern cylinders usually come with foam lagging pre-attached to the outside of the cylinder. Make sure that the new cylinder carries the British kite-mark, to ensure your compliance with Part L of the Building Regulations regarding the conservation of energy.

Older cylinders are likely to be fitted with an insulation jacket which could be as thin as 40mm. These provide little or no benefit and depending on how old the cylinder is, could have worn through in places, or even been wrongly fitted from the start.

If your cylinder does not have lagging, a new 80mm thick insulation jacket should cost no more than £15 and can save up to £30 a year on your heating bills. This should be your highest priority in the event you find yourself with an un-lagged cylinder.

Delivery Times:

The delivery time for a standard hot water cylinder is between 7 to 14 working days.

The delivery time of a bespoke cylinder depends entirely on the specifications the cylinder must be manufactured to, and will be calculated on a case-by-case basis.

Our Recommendation:

Our hot water cylinder manufacturer of choice is RM Cylinders of Yorkshire, an independent company built on a proud tradition of serving the commercial and domestic hot water storage markets.

RM Cylinders specialise in bespoke hot water cylinders, manufactured to precise specifications provided by their customers.

We are proud to work with RM Cylinders as they continue their tradition of providing quality, flexibility and market-leading customer service.

About the Author

This article was written by Sam Brown, Marketing Manager at TradePlumbing. Tradeplumbing.co.uk is a trading name of Clayton Horsnell LTD,a privately held company with headquarters in Colchester, UK, providing a wide variety of plumbing products starting with bathroom suites, baths, showers, towel rails, furniture, sinks, heating system, and radiators and finishing with taps and water treatment products.

Twin Block Braces make me hot?

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Is the brace making me hot, if so how?
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This entry was posted on Saturday, February 28th, 2009 at 6:22 am and is filed under bedding. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.