When it comes to specifying a hot water cylinder, quality and longevity must be a top priority. While on the face of it most cylinders might look the same, on closer scrutiny there are important differences, which can impact on product performance and lifespan.
Unvented cylinders store water under pressure, making it essential that they are strong, durable and corrosion resistant. In the UK, unvented cylinders are, in the main, made from stainless steel, copper or enamelled mild steel. The latter must have a coating or glass lining to make them corrosion resistant, but also need a sacrificial anode to protect areas not covered by the coating. Some cylinders made from low-grade stainless steel also require additional protection, and monitored for signs of wear each year.
By far the preferred material is Duplex stainless steel, as it has outstanding and unique resistant properties. It is also lightweight, giving it a strength-to-weight ratio advantage. For longer cylinder life specifiers should look out for cylinders that combine laser and TIG welding and butt welded joints to avoid crevices.
On a direct cylinder, a titanium immersion heater is an indication of quality, and on an indirect cylinder the material to look for on the element would be Superloy 825. Both are high-grade, but the immersion heater on a direct cylinder needs to be made from a stronger material, as it will be used more frequently than on an indirect model, where the immersion acts only as a back-up.
As well as specifying top-grade materials, leading manufacturers will ensure that their products are energy efficient. Since the introduction of the Ecodesign and Energy Labelling Directives (ErP) in September last year, it has been easier to compare efficiencies like-for-like, with energy labels required for water heaters with outputs of up to 70kW and hot water storage tanks with storage volumes of up to 500 litres. Products in the scope of the directives must also be provided with additional performance and efficiency information via a ‘technical fiche’ within the product data, which can help when comparing products within the same energy band.
When it comes to performance, there are a number of parameters to consider, including improved flow rates, recovery times, standing heat losses, and the amount of stored hot water available. Specifiers should consult manufacturers’ literature, and seek out features including the insulation of the temperature and pressure relief valve, which reduces heat loss, an L shaped heating element rather than a straight one to ensure the majority of the cylinder is heated, and an efficient inlet diffuser that ensures excellent stratification and hot water output.
When weighing up the options, it’s equally important to check whether products have been manufactured to established British and European standards, in a factory which has accredited Quality Management Systems. Third party approvals – such as from WRAS and KIWA – are also a good indication of quality and performance.
Megaflo Eco is the UK’s leading unvented cylinder, with over one million installed across the country. Heatrae Sadia offers a lifetime warranty for any Megaflo cylinder or calorifier installed in domestic properties against corrosion for the lifetime of the owner. For further information, visit www.heatraesadia.com.
