Insulating a hot water tank

LAST UPDATED: 10th January 2023 by The Editorial Team

Summary: Step by step guide and video showing how to insulate a water tank, insulate a hot water tank, insulate a cold water tank, insulate using insulation boards and insulate using an insulation jacket.

How to insulate a hot water tank

If your water cylinders do not have any insulation, then you will need to purchase a cylinder jacket to fit over them. These insulation jackets comprise of several plastic segments and come in various different sizes.

When putting the cylinder jacket on ensure that there are no gaps and the immersion heater cable is on the outside.

Insulating hot water tanks

  • Circular hot water tanks have a range of insulating jackets available. Measure the size of your water tank so you know what size insulation jacket to purchase.
  • When you have got the correct jacket for the cylinder, slide it over the body of the cylinder.
  • You will notice that it is in segments and has straps that run around it so it can be tightened. Follow the manufacturer’s instructions on how to fit the jacket correctly.
  • Make sure you strap the segments of the jacket firmly but do not over-tighten. Also make sure there are no gaps between the segments

Insulating cold water tanks

Water tanks in the loft should be insulated along the sides and should have an insulated lid. The two main types of insulation for a loft tank are insulating boards and insulating jackets.

Insulating boards

  • When using insulating boards, make sure you have the correct size for your tank. It should not leave areas exposed. It is possible to purchase insulating boards of a particular size or to cut the boards to fit.
  • For insulating the top of the tank you will need to have a proper lid installed first, and then the insulation board should be placed on the top. Make allowances for the overflow entering the tank from above.
  • Secure the insulation panels in place using rope or tape. Also be sure that the ballcock can be accessed easily without having to disturb the side insulation at all.

Insulating jacket

  • There are different sizes of insulation jacket available, so try and find the best fitting one for your tank. If your tank is not of a standard size, then you will require a jacket larger than your tank.
  • Do not fit the jacket over the top of the tank, but around the sides. The top should have an insulated lid which is easily accessible. Make allowances for the overflow entering the tank from above.
  • Secure the jacket using the straps, string or tape. Do not over-tighten as this will prevent the jacket from insulating effectively. Also make sure the ballcock can be accessed without needing to disrupt the side insulation.

How to install a lagging jacket to a hot water cylinder video

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The Editorial Team

The Editorial Team at lets-do-diy.com are a team of experts led by Mark Wilson. We have been creating DIY projects, articles, costs guides and product reviews since 2008. For more info see our about page.