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How to insulate a cold water tank

Wrap an insulating jacket around the tank for cold weather protection

When winter weather hits we work hard to protect our homes. But all too often we forget areas that are out of sight, such as the loft. Cold water tanks housed in the loft can freeze when temperatures drop. Thankfully, it’s easy to help prevent this and protect them for years to come by lagging your cold water tank with an insulating jacket.

This simple but effective item wraps around the tank to insulate it, keeping the water stored inside warmer than it would be without the jacket. This means less energy is used to heat the water, so you can save money on your energy bills.

In this guide we’ll provide step-by-step advice on how to:

  • Choose the right insulating jacket for your cold water tank
  • Fit the jacket to your water tank.
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Safety kit and Safety first

Before tackling any loft project, head to our guide on loft safety.

It includes essential advice on how to move and work safely in the loft, as well as a full list of recommended protective clothing and other loft project must-haves. These items are not included in this article's list of materials and tools. Be sure to read and check you have everything you need to safely start insulating a cold water tank in your loft.

Ensure that the water tank jacket is not in close proximity to heaters, light bulbs or other sources of heat.

What water tank jacket is needed?

Before you can lag your water tank, it’s essential to confirm its shape and measure its size. This will ensure you buy the right size of tank jacket to best fit. This means a trip into the loft.

Step 1

In the loft, measure the size of the water tank.

Rectangular water tanks - measure and note the length, width and height of the tank. Circular water tanks – measure the circumference and height of the tank.

You might find that you have two water tanks in the loft, so measure both individually. Choose the jacket(s) that best fit your tank(s) based on these measurements.

Top tip: Tie loosely

Don’t over-tighten the straps, the panels insulate more effectively if they’re not compressed.

Top tip: Insulate water pipes

We recommend that all water pipes entering the tank should also be insulated. For advice on this, head to our guide on insulating water pipes.

An insulation jacket typically has two panels - a long panel to fit around the sides of the tank, and a short panel to fit over the tank lid.

Step 1

Check if there is any loft floor insulation under the cold water tank.

If the tank is elevated by at least 300mm - leave it where it is. If the tank isn't elevated by at least 300mm - remove it. Don't block the heat coming up through the ceiling as it can actually help keep the tank warmer and prevent freezing during cold winter weather.

Step 2

In the loft, open the packaging being careful not to rip the jacket.

Unroll the tank jacket panels and give them a gentle shake. Leave for approximately one hour to allow the insulation filling to expand.

Step 3

Place the smaller lid panel over the tank lid and check that there's an equal overhang around the edges.

Step 4

Use a utility knife to cut holes through the jacket lid panel for any protruding pipes or vents from the tank's lid.

Secure the overhang to the tank with electrical insulation tape.

If your water tank doesn't have a lid - securely fit the insulated lid panel with tape at both ends and sides of the tank.

Step 5

Wrap the longer panel around the tank, starting at the centre of one of the shorter sides if wrapping a rectangular tank.

Step 6

Once all sides of the tank are fully covered, loosely tie the jacket using the ties provided.

Space the ties evenly with the top set tied one third from the top and the lower set tied one third up from the bottom of the tank.

It can be fiddly to tie the jacket into place - use small pieces of tape to hold it in position as needed.

Step 7

Check if any overhang from the lid panel is tucked inside the main body of the jacket panel. Adjust as necessary so that the tank is completely covered.