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Hot Water Cylinder Guide

When it comes to hot water cylinder there is a lot of jargon and technical terms involved that can be quite confusing for those not proficient in the terminology. The good news is that once you understand the various terms, getting to grips with what a hot water cylinder is and how a hot water cylinder works is relatively straight forward.

The good news is if you are looking for a new boiler for your central heating, then it isn't as difficult as it might seem to understand the name, types and components that go to make up a central heating system. Generally speaking, when it comes to boilers there are only three main types of boiler available, and these are the ones typically found in your home

What is a Hot Water Cylinder

In simple terms a hot water cylinder is a water storage tank that is used to contain hot water in certain types of central heating system. This hot water tank is used to provide hot water to your taps and shower. You'll often find the hot water tank in the airing cupboard in your house if you have one of these tanks. Not all central heating systems use a hot water cylinder. For example, central heating systems with a combi boiler do not need one as this boiler type heats the hot water on demand and doesn't need to store any hot water. Traditional boilers and system boilers that are alternative central heating system set ups will require a hot water storage tank.

Different Types of Hot Water Cylinder

The type of tank that you require is based on several factors. Firstly, the type of central heating system that it is being connected to, will have an impact on the type you will need. The other factor is how the water in the tank is to be heated.

Heating Water

Direct Hot Water Cylinders

This type of hot water storage cylinder has a mechanism to heat the water itself. The way this works is through something called an immersion heater element that is found inside the cylinder. Hot water is heated by the immersion heater element when it is required. Often when hot water is needed the immersion heater is turned on with a switch, found close to the cylinder. Once the water has been heated the immersion heater is then turned off. Cold water comes into the water cylinder it is heated by the immersion heater and when water, such as a tap is turned on, the water flows out of the cylinder. The principle is very like a kettle that contains an element and the water is heated directly by the element, the kettle just being the container of water. This type of water heating is called Direct and we would always suggest a timer to control the appliance. This is what makes up the hot water supply in the home.

If you're looking to buy a direct hot water cylinder browse our current range at Mr Central Heating

We recommend the following direct hot water cylinder:


     Everflo 150 Litre Direct
     Everflo WM100 POU
     UV Gold 90 Litre DirectK

Indirect Hot Water Cylinder

Another type of cylinder that is used in domestic hot water situations is the indirect hot water cylinder. The way an indirect cylinder works is that an external source is used to heat the water prior to being transferred to the indirect cylinder. A central heating boiler may be used for this purpose, or another external heating source such as solar panels, for example. Cold water is drawn into the tank from a water source. This is often a cold-water storage tank but an unvented cylinder will take the water directly from the mains. An item called a heat exchanger is contained within the storage tank. This takes the form of a heating coil, and hot water from the boiler or alternative heating source passes through this heating coil, in turn heating up the water within the indirect hot water cylinder. The hot water once it passes through the heat exchanger moves back out of the cylinder back to the heating source to repeat the process. The water from the boiler and the cylinder itself are therefore kept separate.

As water passes through the heat exchanger it heats up the cold water in the cylinder. This cylinder then acts as a thermal store for the hot water. Since heat rises, the hot water typically remains at the top of the tank closest to where the feed to the household pipework is. Since cold water travels to the bottom of the storage tank, it is closest to the heat exchangers and the external heating source. With this structure, the household has access to hot water and the water within the tank remains warm.

It should be noted that in some situations it is also possible to find an immersion heater in an Indirect hot water cylinder too. This allows for a secondary water heater, if the primary heat source is not available (solar for example) or an added boost is required

Look at our a great range of indirect water cylinders that we stock at Mr Central Heating.

We recommend the following indirect hot water cylinders:


     Everflo 210 Litre Indirect
     Ideal System Ready 300 Litre Indirect
     Everflo 210 Litre Indirect System Fit

Different Types of Hot Water Cylinder

Vented Cylinders

These cylinders requires connection to a cold-water tank which feeds the cylinder with cold water. This tank is also known as a feeder tank. Generally, this type of cylinder will connect to a large water tank in the loft via a vent pipe. It is common to find this type of cylinder in a traditional central heating system. This type of storage tank uses gravity to help distribute water around the home. This can mean that water pressure on showers may be a little bit on the low side and an additional pump might be required to get a better-quality shower. This type of cylinder is not dependent on mains pressure, so if the water pressure is very low, these tanks are still viable.

Explore our comprehensive range of vented water cylinders that we stock at Mr Central Heating.

We recommend the following vented hot water cylinder:


     Ideal Envirofoam 900 x 400 Indirect
     Ideal Envirofoam 1200 x 450 Indirect
     Ideal Envirofoam 1050 x 450 Indirect

Unvented Cylinders

When it comes to unvented hot water cylinders the main difference between these and their vented cylinder cousins is the fact that they use the mains water supply for its water requirements. One of the benefits of the unvented system vs the vented storage system is that this type of cylinder does not require a cold-water storage tank in the loft itself. This can help save a lot of space. This type of cylinder is commonly found used with system boilers. This type of system can be used in most homes, although if the mains water pressure flow rate is very low then it may not be appropriate. The cost more than the vented cylinder type but are more energy efficient and last longer because they are made from stainless steel.

Learn more about the unvented hot water cylinders that we stock at Mr Central Heating.

We recommend the following unvented hot water cylinder:


     Ideal 250 Litre System Ready
     Everflo 210 Litre Horizontal
     Everflo 300 Litre Indirect