PHAM NEWS | MAY 2025 Water Heating& Cylinders 21 Choosing the right cylinder


With so many hot water cylinders available, it is not surprising that many homeowners can get confused about the diff erent options, but how can you ensure that you install the best solution that will meet their requirements? David Hall from Intergas Heating provides a useful buyer’s guide.


D


espite serving a seemingly simple purpose, there are a wide range of diff erent hot water


cylinder styles and sizes to choose from. Which cylinder type your customer will need will depend on how it’s heated, as well as how much hot water they require (determined by their home size and personal habits). Hot water cylinders are grouped into two primary sets – open vented and unvented – but within these categories there are a large number of diff erent designs.


For homes with two or more bathrooms and a high demand for continuous hot water, a heating system with a storage cylinder should ensure their needs are always met. 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. However, if a larger cylinder


is being considered, it is vital to make sure that there is suffi cient space in the existing location to comfortably fi t 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 fi t in the current space.


Cylinder construction With so many cylinders to choose from, how can you be sure that the cylinder you select is the best and value for money? Let’s take a look at some of the key factors that should infl uence your decision. Stainless steel is a generic


name for more than 150 carbon alloys that have a minimum of 10.5 chromium. Chromium makes stainless steel corrosion-resistant by oxidizing quickly, forming a thin layer on the metal surface that protects the underlying metal from corrosion. With this thin passive fi lm completely covering the metal surface, the metal is passivized, and the risk of corrosion is greatly reduced.


The most commonly used


grades of stainless steel employed in hot water storage are 304 and 316(L) which have a higher level of corrosion resistance and the ability to shape and form the metal into cylinders and heat exchangers (coils).


As with boilers and heat pumps, when it comes to DHW


David Hall Intergas Heating UK & Ireland business development director


 Manufactured from 444 stainless steel, the Intergas Xylinder heat pump cylinder range has been designed to work in harmony with Intergas Xceed heat pumps and features a smooth internal coil to maximise heat transfer and reduce running costs


 The Xylinder Direct cylinder is available in 150 to 300 litre models and features an immersion heater which sits above the coil so it only heats up the water required


storage vessels, materials are also best selected for their heat performance properties. As the heat exchanger (coil) plays a key role in maximizing eff ective and reliable heat transfer, stainless steel off ers a robust, long-lasting solution. Frequently confronted with minerals, oxygen, chemicals and sediment, not to mention high temperatures and thermal stress, stainless steel is, without doubt, a strong, durable contender that can withstand water attacks. In comparison to coils made from steel or copper, stainless steel is a good material choice due to its high corrosion resistance and fl exibility. Also, due to their composition of corrosion- resistant alloys, stainless steel products often have a longer warranty. Stainless steel DHW cylinders also have the added advantage of being lightweight. Featuring a typically much thinner wall, this makes them much easier and safer to transport and install.


Understanding grades When it comes to selecting the appropriate material for a hot water cylinder, stainless steel stands out for its durability and resistance to corrosion. However, not all stainless steel is created equal. Diff erent grades of stainless steel off er varying properties and are suited for specifi c applications. Understanding these grades can help in choosing the right type of stainless steel cylinder, ensuring optimal performance and longevity. Grade 304 is the most commonly used stainless


steel grade. It belongs to the 300 series of stainless steel and is known for its excellent corrosion resistance and high formability. It contains 18% chromium and 8% nickel, which contribute to its resistance to oxidation and corrosion. Due to its robust properties,


Grade 304 stainless steel is often used in residential and commercial cylinders. It is suitable for environments where the water is not excessively acidic or alkaline. Its resistance to rust and stain makes it a popular choice for many water storage applications. Stainless steel 316 grade is known for its superior resistance to corrosion, particularly in chloride environments. It is also part of the 300 series but includes


molybdenum, which enhances its corrosion resistance. This grade contains 16% chromium, 10% nickel, and 2% molybdenum. Grade 316 is often used in


water tanks exposed to harsh conditions or high salinity environments, such as coastal areas or industrial applications. It is particularly useful where the water may be more corrosive, such as in marine or chemical environments. Grade 444 is a stabilised chromium-molybdenum ferritic stainless steel, combining very good corrosion resistance with good formability and weldability. Its excellent corrosion resistance enables it to replace grade 316 in many applications – domestic hot water cylinders are its largest fi eld of application. This grade contains 18.5% chromium, 1% nickel, and 2% molybdenum. Grade 444 has very good


resistance in a wide variety of corrosive media. The resistance of grade 444 to pitting and crevice corrosion in chloride environments is similar or superior to that of grade 316. Chloride stress corrosion


cracking (SCC) resistance of 444 is also very high due to its low nickel content. Choosing the best grade of stainless steel hot water cylinder involves considering factors such as the environmental conditions, water quality, and the specifi c requirements of the application. Grades 304 and 316 are commonly used for their excellent corrosion resistance, durability and cost. For peace of mind and reliability, Grade 444 stainless steel off ers superior strength and resistance. By understanding the distinct


properties of each grade, you can make an informed decision that ensures long-lasting and reliable hot water storage solution.


Which size?


Obviously larger houses will need a larger cylinder, but when selecting the size of the hot water cylinder, a simple rule of thumb is that for a typical domestic household,


you should allow between 45 and 50 litres for every occupant. That said a mains pressure system can use about


12 litres of water per minute at 40°C if a decent quality shower head is used. Certain brands of shower can use up to 25 litres of water per minute.


However, it must be noted


that personal habits also play a big part in total hot water use. Two households of the same size can use completely diff erent amounts of hot water, with one of them using twice as much as the other! In determining how much hot water is required, you should always consult with the occupants, and consider the following: • A bath uses 100 litres of hot


water at 40°C (equating to 60 litres at 60°C) • Showers can use about 12


litres of hot water per minute at 40°C (equating to 11 litres at 60°C)


The following average


consumption values can be used as a general rule (hot water requirements per person per day): • Low consumption = 20 to 30


litres • Average consumption = 30


to 50 litres • High Consumption = 50 to


70 litres On this basis, a typical four


person household would often use around 200 litres of hot water a day and this is the fi gure that will generally be used under the EU energy labelling scheme. This does not necessarily mean that a 200 litre cylinder is required, as the cylinder may be partially reheated during the day. It is up to the installer to match the correct size of cylinder relative to boiler (or electrical) input to avoid running out of hot water. ◼ phamnews.co.uk/525/31


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