Hot Water Storage: The Options

hot water storage units from Begetube. Begetube’s two phase change material units (each contain 60 litres of hydrate salt) provide the same level of thermal storage as the 600 litre thermal store next to them
Begetube’s two phase change material units (each contain 60 litres of hydrate salt) provide the same level of thermal storage as the 600 litre thermal store next to them (Image credit: Begetube)

A hot water cylinder once was just that — a cylinder that contains hot water. Usually copper, often with a 80 litre capacity, and sometimes with an immersion heater, this simple device did exactly what the name suggested. But now we have buffer tanks, accumulators, thermal stores and even calorifiers. What happened?

With the increasing need for efficiency, more complex heating control systems and the potential for multiple heat sources, a simple cylinder is no longer always the answer. The problem is knowing what all these different devices do and which one to specify.

Tim Pullen

Tim is an expert in sustainable building methods and energy efficiency in residential homes and writes on the subject for magazines and national newspapers. He is the author of The Sustainable Building Bible, Simply Sustainable Homes and Anaerobic Digestion - Making Biogas - Making Energy: The Earthscan Expert Guide.


His interest in renewable energy and sustainability was first inspired by visits to the Royal Festival Hall heat pump and the Edmonton heat-from-waste projects. In 1979

this initial burst of enthusiasm lead to him trying (and failing) to build a biogas digester to convert pig manure into fuel, at a Kent oast-house, his first conversion project.


Moving in 2002 to a small-holding in South Wales, providing as it did access to a wider range of natural resources, fanned his enthusiasm for sustainability. He went on to install renewable technology at the property, including biomass boiler and wind turbine.


He formally ran energy efficiency consultancy WeatherWorks and was a speaker and expert at the Homebuilding & Renovating Shows across the country.