Is your Hot Water Cylinder insulation below standard?
An hot water cylinder heater is rather like a large kettle. It is an electric resistance loop that is inserted into a cylinder to heat stored water. Immersions are not the most efficient way of heating water in the home, but they do have the advantage of flexibility and ease of use, and they can be used on an economy night tariff electricity supply via a timer.
Homes without boilers generally rely on hot water cylinders with an immersion heater for their primary hot water supply. Many other houses with central systems have an immersion as a back up to provide hot water in case of boiler failure.
A typical immersion heater uses 3kW of electricity an hour, and costs around £1 for two hours’ use on an average standard tariff, or perhaps a half of this on an Economy 7 tariff. This will generally provide the daily basic hot water needs for a small, one or two person household.
A large tank of expensively heated hot water will lose heat very quickly if not used immediately. Insulation is critical to energy efficiency, financial savings and minimising carbon emissions. It also makes for a more convenient system, as hot water will be instantly available without waiting for the tank to heat up again.
Modern cylinders are factory-fitted with insulation, generally in the form of a 50mm foam coating. While this is usually sufficient, even relatively new tanks may have an out-dated coating of 38mm or less, as insulation standards have increased substantially over recent decades. The thickness can be measured where the foam is cut away to allow the insertion of the immersion heater assembly. Any sign of copper means that there is an easy escape route for the heat.
An older hot water cylinder without foam or with a substandard layer can be insulated with a purpose-made jacket. These are widely available from DIY stores. It is worth paying a little extra for a thick jacket if there is room around the tank to accommodate it. The best cylinder jackets have a 75mm or 80mm glass fibre filling and a flame-retardant cover, and these can be bought for as little as £15. DIY fitting is straightforward, but remember not to cover the top of the immersion heater and its thermostatic cut-out.
Adding one of these jackets to an un-insulated tank can save around £80 a year on electricity bills, so the investment will pay for itself within three months. It will also reduce your annual household carbon emissions by 420kg. Using a jacket to top up a cylinder with 25mm of foam will save approximately £20 per year, with payback over nine or ten months.
It is also worth lagging the exposed hot water pipes in the immersion cupboard. These take the water from the top of the tank to the shower and taps. The sections closest to the tank can lose a lot of stored heat, and they can be very easily insulated with split foam tube that simply slips over the pipe and closes around it. This is a £20 DIY job that will save another £10 to £20 a year.