Hot Water Cylinders

Hot Water Cylinders 2018-01-31T15:57:29+00:00

Hot water cylinders are a must with regular and system boilers, and come in a variety of sizes. It is probably advisable, especially with a family, to have the largest you can find space for. The capacities can range from around 100 to more than 300 litres.

Check with your installer that the boiler you are buying will heat the amount of water you want to be stored, and how long it takes to heat the cylinder from cold – if you should run out. Cylinders need to be well insulated to ensure the maximum heat retention.

Modern hot water cylinders come already insulated, but if you have an older version then it is possible to buy an insulation jacket from a good DIY store. The money saved through retained heat will ensure it soon repays the cost.

Choosing a standard hot water cylinder

When choosing a hot water cylinder the first decision that needs to be made is whether you choose a traditional cylinder with a separate header tank or a combined unit.

Traditional cylinder

The traditional hot water cylinder is used in many family households in the UK and is suitable for a variety of heating systems e.g. electric,coal oil and gas fired heating systems.

The cylinder is fed by a cold-water storage cistern usually located in the attic, which provides a greater head of water, thus a higher flow rate at the taps, than combination type cylinders.

Combination cylinder

A combination water storage cylinder has its own cold-water header tank fitted on top of the hot water cylinder. They come in a variety of sizes, 115 litres of hot water storage being the most common with 20 -115 litres of cold storage on top depending on the circumstances Intergrating a cold water cistern and a hot water cylinder in a compact all-copper unit, are an effective way of providing adequate supplies of hot water when storage space is limited, it also enables a ‘dry loft’ thus lessening the risk of freezing. This system is ideal for rented accommodation due to is low maintenance requirement, or partially used properties where frequent draining and re filling by the owner is required.

The next step is to determine which mode of heating you will use to heat your water, this will determine whether a heat exchanger will be required for central heating use.


Hot water from the boiler circulates directly through the cylinder. Alternatively used for all electric immersion heater operation.


Hot water from the boiler circulates through a heat exchanger (usually a coil) within the cylinder. Avoids the problems of mixing boiler water with the water in the storage vessel.

Self priming

Incorporating a patented heat exchanger designed to provide two airlocks to prevent water mixing. This system also removes the need for a separate expansion and feed system for the primary circuit.

The next decision is to determine the overall size and water storage capacity of the cylinder.

Hot water usage varies with the type of building, it uses and the number of occupants. Occupant usage may vary depending on their level of activity, age, and water usage by appliances etc.
In modern homes hot water usage can vary between 35 and 45 litres per person per day, with hot water at between 60 – 65 degrees centigrade.

  • A wash hand basin tap will use 0.15 litres per second at 40 degrees C
  • A Kitchen sink will use 0.20 litres per second at 60 degrees C
  • An average bath can use 60 liters of hot and 40 litres of cold water
  • Modern showers can use 11 litres of blended water per minute.