Don’t fit a “standard” cylinder, fit something better!

The unvented cylinder industry is a crowded market, with many suppliers chasing a finite amount of business. Installers clearly have a choice in the products they buy, but in an increasingly commoditised market, they often may not know too much about the product they end up fitting in a consumer’s property. 

If there is a “standard” cylinder, it is a stainless steel cylinder with a separate expansion vessel that is around 200 litres. “Standard” is OK, but its not the best for many occasions.

The OSO super Series is anything but standard. It is a virtually pre-plumbed cylinder that has heating coil connections, hot and cold water services, safety valves and expansion vessels all concealed and contained under a removable lid. Pipes and cable are invisible and usable space is optimised to allow more space for towels and linen storage.

The end result is a dramatically neater and more space efficient cylinder package that considerably reduces installation time and frees up space in a cylinder cupboard that will have customers purring with delight compared the random clutter of pipes and expansion vessels that comes with “standard”. 

With these and other differences, nothing is for free. Some manufacturers will strain every sinew to make the product as cheap as possible to buy, OSO invests heavily in new technology to improve the design, efficiency and ease of fitting of the worlds most advanced water heaters. 

Space efficiency is always important to a householder. The cylinder should be shaped to the area available. Slimline cylinders are available where cylinder spaces are narrow, in all other occasion, wider is better. All manufacturers make similar capacities, but a small increase in diameter can significantly reduce height in a cylinder, allowing more storage shelves or even a washing machine to be fitted in the same cupboard. This is achievable at up to 210 litres with the OSO Super. 

A wider cylinder loses less heat and contributes to better ERP ratings and SAP values. A perfect water heater in terms of heat loss would be spherical. Practical considerations mean that water heaters are cylindrical, but short and fat is better than tall and thin. As close as you can get to 600mm diameter is optimal for most airing cupboards. 

When you have anything other than gas central heating, “standard” is not an option. Manufacturers will typically offer of full range of direct electric, and renewable heat source cylinders for heat pump and solar thermal to complement the standard indirect. Most of these will be offered in capacities typically up to 300 litres.

If you have a heat pump, fit a heat pump ready cylinder. A standard indirect does not have the heat exchanging power needed from the low grade heat from a heat pump. Pay careful attention to the heat exchanger, particularly to how it is designed. A smooth coil will not encourage limescale accumulation, so in hard water areas, be wary of alternative types of heat exchanger where limescale could accumulate and reduce efficiency.

ERP energy labels have revolutionised the heating and appliance industry. Cylinders below band C are effectively illegal. A is best and A is available up to 300 litres in the form of the OSO Delta. A Delta 300 compare to an older unit from the turn of the millennium can save close to £100 per year on a gas fired central heating system, with greater savings on electrically heated cylinders. Most modern cylinders are insulated with Polyurethane foam however efficiency levels are further improved by the pioneering Delta and Super Series cylinders fitted with vacuum panel insulation.

Vacuum panels are very “non-standard”, but to any customer looking for energy efficiency and low fuel bill, they are the best way forward for water heating.

The Hot Water Association Charter identifies manufacturers whose products have passed a high level of audit and scrutineering to demonstrate that the products are honestly and correctly labelled and performance claims are independently verified. Charter members, including OSO Hotwater can be found at  

Heat up time has in recently given way to heat loss efficiency as the benchmark of performance, however if very large volumes of hot water are required, perhaps in commercial circumstance, customers should look for high specification coils to provide a fast recovery rate. Very often this could mean a heat pump cylinder with a big heat exchanged connected to a gas powerful boiler to maximise recovery time.

Unvented cylinders are not all the same. Quality, efficiency, design ingenuity and price all vary. The end customer will not always be interested in the same features as an installer, and giving an end user alternatives at differing prices can lead to both a happier customer and a more profitable project for the installer.