If you have a hot-water cylinder, wrapping it properly is about the quickest payback you will find anywhere in the house. You have already paid to heat that water. An insulating jacket simply stops it going cold while it sits in the cupboard waiting to be used, so the boiler or immersion does not have to reheat it as often. The materials cost less than a couple of takeaways, the fitting takes minutes with no tools, and the saving repeats every single day. This guide covers what to buy, how much it really saves, and the pipes most people forget.
The short answer. An uninsulated copper cylinder loses heat constantly, and a good thick jacket cuts that standing loss enough to save in the region of 40 to 70 a year for a typical household. The jacket costs around 15 to 30 and pays for itself in a few months. Foam lagging on the pipes adds a little more saving for a few pounds. If your cylinder is bare or thinly clad, this is the best-value job in the house.
Why a bare cylinder costs you money every day
A hot-water cylinder is a tank of water you have paid to heat, sitting in a cupboard cooling down. Every degree it loses, the boiler or the immersion heater has to put back, and you pay for that energy twice over.
An uninsulated copper cylinder sheds heat fast. Touch a bare one and it is warm to the hand, which is heat escaping into the cupboard rather than staying in the water. A thick insulating jacket slows that standing loss dramatically, keeping the water hot for far longer between heat-ups, so the heat source fires less often.
Even cylinders with a thin sprayed-on factory foam layer benefit from a jacket over the top, because the original foam is often thinner than ideal. The colder the cupboard the cylinder sits in, the more a jacket saves, since the temperature difference driving the heat loss is larger. This is the same hot-water economy covered on the hot water savings page.
What it actually saves
Standing loss from a cylinder is real energy, and cutting it is cheap. Here is a rough breakdown of where the savings sit, depending on how your water is heated.
| Job | Rough cost | Typical annual saving |
|---|---|---|
| Jacket on a bare cylinder (gas heated) | 15 to 30 | 40 to 70 |
| Jacket on a bare cylinder (immersion heated) | 15 to 30 | 100 to 180 |
| Jacket over thin factory foam | 15 to 30 | 15 to 35 |
| Foam lagging on accessible hot pipes | 5 to 20 | 10 to 20 |
At 26.11p per kWh electricity and 7.33p per kWh gas, Ofgem cap July to September 2026. Savings vary with cylinder size, cupboard temperature and how the water is heated. Electric immersion heating saves far more because the fuel is dearer. Worked examples; check your own setup.
The standout is a cylinder heated by electric immersion. Because electricity is roughly three and a half times the price of gas per unit, every kWh of standing loss you stop is worth more. A jacket on an immersion-heated cylinder can pay for itself in a couple of months. Gas-heated cylinders save less in cash terms but still pay back inside a year.
Choosing and fitting a jacket
The rule is simple: the chunkier the jacket, the better. Look for a generous thickness, usually quoted as 80mm or more of insulation, sized to your cylinder's height and girth. A thin token jacket does far less than a proper thick one, and the price difference is small.
Fitting is a job anyone can do with no tools:
- Wrap the segments around the cylinder so they cover the sides and the top.
- Tie or strap them into place with the loops or bands provided.
- Leave the thermostat dial, the immersion boss and any controls accessible, so you can still reach them.
- Do not cover any valves or the pipework connections you might need to get at.
It takes minutes. If the cylinder sits in an airing cupboard you use to dry clothes, bear in mind a good jacket keeps that cupboard cooler. That is the whole point: the heat stays in the water instead of warming the cupboard, so you may need to dry clothes another way. Our notes on drying clothes without a tumble dryer cover the cheap options.
Do not forget the pipes
The pipes leaving the cylinder lose heat just as the tank does, and they are even cheaper to insulate. Foam pipe lagging is a slit tube that pushes straight onto the pipe by hand and cuts to length with a knife. It costs very little per metre.
Prioritise:
- The first stretch of hot pipe leaving the cylinder, where the water is hottest and the loss is greatest.
- Any hot pipe running through an unheated space like a cupboard, loft or under the floor.
- The pipes between the boiler and cylinder on a system with a separate boiler.
Lagging the hot pipes keeps the water hotter on its way to the tap, which means less cold water run off before it arrives. While you have the foam out, lag any cold pipes that run through an unheated loft too. That does not save energy, but it protects them from freezing and bursting in a cold snap, which is a far bigger bill to avoid. The same loft is worth checking for loft insulation depth while you are up there.
Which cylinders are worth it, and which are not
Not every modern cylinder needs a jacket, so it is worth knowing where the effort pays and where it does not.
- A bare copper cylinder. The best case. These shed heat fast, so a jacket is the single best-value job in the house. Do it first.
- A cylinder with thin factory foam. Still worth a jacket over the top if it feels warm to the hand, since the original layer is often thinner than current standards.
- A modern foam-clad cylinder with a thick factory layer. Usually has 35mm or more of bonded foam and feels cold to the touch when full of hot water. A jacket adds little here, so spend your effort on the pipes instead.
- A combi boiler system. If you have a combi rather than a stored cylinder, there is no tank to insulate, because the boiler heats water on demand. Lagging the hot pipe runs is still worthwhile.
The simple test is your hand. Run the hot water so the tank reheats, then feel the cylinder. Warm means heat is escaping and a jacket will pay. Cold means it is already well insulated. The same logic applies to where you spend on the rest of the house, covered in quick wins under a tenner.
While you are in the cupboard
A jacket and lagging stop the loss, but you can also cut the loss at source by not keeping the water hotter than you need.
Set the cylinder thermostat to a sensible level rather than scalding. Around 60C is the usual recommendation: hot enough to keep the tank safe from bacteria but not so high that you are maintaining water far hotter than you ever use and then mixing it back down with cold at the tap. The hotter you hold the tank, the faster it loses heat, so a sensible setting compounds the jacket's benefit. This is covered in full on the hot water savings page.
It also helps to heat the water only when you need it rather than holding a full tank hot around the clock. A timer that heats the cylinder before the morning and evening you actually use hot water, and lets it cool the rest of the day, cuts standing loss further. A well-jacketed tank holds its heat for hours, so a single morning heat-up can last well into the evening.
If you heat the cylinder on a cheaper night rate, time the immersion to come on then. The Economy 7 and night rates guide explains how to make the most of off-peak electricity, and the better insulated the tank, the longer that cheap heat lasts into the day. The whole exercise, jacket, lagging and a sensible thermostat, is an afternoon and a small spend for a saving that repeats every single day. For the wider picture on cutting hot water cost, the low-flow showerhead and hot water savings pages are the next read.