Wrap a British Standard insulation jacket around your hot water cylinder to cut heat loss and lower bills.
CJ-01Turn off the immersion heater and let the cylinder coolSwitch off the immersion heater at its own switch, usually on the wall near the cylinder. If the cylinder has been heating recently, leave it an hour so it's not hot to touch. Clear the airing cupboard or space around it so you can work all the way round.
CJ-02Measure the cylinderMeasure the height from base to the top dome, and the circumference (wrap a tape measure right round it). Note both figures in mm or metres. Jackets are sold by these sizes, so buying the right one first time saves a wasted trip.
CJ-03Buy a British Standard jacketChoose a jacket marked BS 5615, at least 80mm thick, sized to match your measurements. Cheaper unmarked jackets can be thinner and less effective, so check the label before you buy.
CJ-04Check the cylinder for leaks or damage firstLook over the whole cylinder and its pipework for damp patches, rust staining or drips before you cover anything up. Fitting a jacket over an existing leak just hides the problem. Sort any leak first, or get a plumber to look, before insulating.
CJ-05Wrap the side segments around the cylinderMost jackets come as several curved segments. Starting at one point, wrap each segment round the cylinder in turn, matching the curved edges so they overlap slightly with no gaps. Keep the insulation side facing the cylinder.
CJ-06Secure the strapsTie the fixing tapes or straps supplied with the jacket, working from top to bottom, pulling each one snug so the jacket sits close to the cylinder without gaps. Don't overtighten to the point of squashing the insulation flat, as this reduces how well it works.
CJ-07Fit the jacket around pipework and the immersion heaterCut or ease slits in the segments so they sit around pipes and the immersion heater housing without squashing them. Leave the immersion heater thermostat dial and switch fully accessible — you'll need to see and reach these later.
CJ-08Fit the top piecePlace the top segment over the dome of the cylinder, tucking it in around the vent pipe and any control valves. Leave the temperature and pressure relief valve fully clear and visible, as this needs to be checked periodically.
CJ-09Check the fit and tidy upRun your hand around the jacket checking for gaps or loose straps, and adjust as needed. Clear away packaging and offcuts, then switch the immersion heater back on. You should notice the cylinder stays warmer for longer and your bills should drop slightly over time.
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