A poorly insulated hot water cylinder will constantly lose heat into the surrounding area which you may not want to be heating. For example, an electric immersion hot water cylinder without any insulation will lose so much heat it will actually heat the property for you, but this type of heating is very costly to run. Tested and approved at British Standards Institute (BSI Testing Hemel Hempstead) Licence No: KM36881. Multi Panel (4) design to meet the heat loss requirements of BS 5615: 2007(not more than 2.5KW per 24 hour standing heat loss) Eyelet incorporated with one top tie cord and four lengths of heavy duty fixing tape for ease of application. potential savings are calculated using RdSAP 2009 energy assessment software which is used for residential energy performance certificates.