When it comes to insulating your cold water storage tank and central heating expansion tank (if you have one), there are a number of options open to you. If your tank is circular you could cover it with a proprietary jacket consisting of a number of polythene or plastic envelopes’ filled with insulant; or you could simply wrap it up in a layer of mineral wool or glass fiber blanket similar to — or even the same as — that which is used to insulate loft floors. If, on the other hand, your cold water tank happens to be rectangular then you could construct a ‘box’ for it yourself out of expanded polystyrene, or buy a proprietary one ready-made. A proprietary jacket couldn’t be easier to fit: you simply pull it into position and then tie it in place tapes are sometimes provided by the manufacturer. If you have to cut into the jacket to accommodate a pipe, make sure that you seal it up again with plastic adhesive tape to prevent moisture getting in and the insulating material from escaping.
Expanded polystyrene kits are so extremely easy to fit. Apart from having to fix the pieces of polystyrene together with tape, string or polystyrene cement, the only work you will have to do is to make cut-outs for the pipework. More work will be required should you decide to make your tank kit out of sheet polystyrene — but it would of course be a lot cheaper. If you decide to use insulation blanket to lag your tank then try to buy the sort that is bonded with paper as you will find it much easier to handle. Buy a roll that is as wide as your tank is deep if you can, as this will save you the trouble of having to go round the side of your tank twice. The thickness of the blanket isn’t critical, but blanket 50mm (2in) thick will give your tank adequate insulation and be easier to work with than a thicker one. However, it could well be that you have an odd roll or two of blanket left over from some previous insulation job; if you do, then use that rather than going to the expense of buying additional rolls. The top of the tank to be insulated must have a firm covering to prevent the water inside being contaminated by fibers from the blanket you are fitting. So if it doesn’t already have a lid, cut one out of hardboard, polystyrene or some other sheet material. Lagging a tank with blanket insulation is simply a matter of common sense. You cut the blanket to size, drape it round the side of the tank, and having cut slits to enable the blanket to fit round the pipes, secure it with string. The lagging on the lid should overlap the side lagging by about 150mm (61n); and as you’ll need to inspect the inside of your tank from time to time make sure it’s easily removable. Under normal circumstances the bottom of your tank should not be insulated, nor should the loft floor directly below. The reason for this is that it allows heat from the house to rise up through the floor and slightly increase the temperature of your cold water. The only circumstance in which you do insulate these places (and this applies regardless of what form of insulation you are using) is when, in order to increase the water pressure for a shower on the floor below, the tank has been raised more than a foot or so above the joists. Insulating hot water tanks
Although you could in theory lag your hot water tank by adapting any of the methods that are used for cold water tanks, in practice you will nearly always find that you have no choice but to use a proprietary jacket. The fact that most hot water tanks are situated in airing cupboards means that blanket insulation is out of the question, and unless your tank is a rectangular one (which these days are very rare) you won’t be able to use polystyrene.