How do I insulate pipes and a hot water tank?

Heat lost from an uninsulated cylinder or from hot pipes running through cold spaces is heat you paid for and never used. Lagging is one of the few home improvements with a payback measured in months rather than years, and it also prevents frozen pipes.

What you'll need

• Foam pipe lagging
• Cylinder jacket
• Scissors or a knife (optional)
• Tape (optional)

Step by step

1. Measure the pipe diameter and length before buying.Lagging comes in sizes to match common pipe diameters. The wrong size fits poorly and insulates badly.
2. Prioritise pipes in unheated spaces.Lofts, garages, under floors, outbuildings. These lose the most heat and are where pipes freeze in winter.
3. Then insulate hot pipes near the boiler and cylinder.The first couple of metres from either lose a surprising amount, and they are the easiest to reach.
4. Cut the foam along its slit and press it onto the pipe.Most lagging is pre-split. Push it on so it closes fully and tape the seam.
5. Do not leave gaps at bends and joints.Mitre the ends to fit around bends and tape them. Gaps are where the heat escapes, and a poorly fitted job loses much of the benefit.
6. Fit a jacket to an uninsulated hot water cylinder.At least 80mm thick. Many older cylinders have nothing, or a thin old jacket worth replacing.
7. Do not insulate under the loft insulation on cold water tanks.Insulate the tank sides and top, but leave the ceiling below it uninsulated so warmth from the house below keeps it from freezing.
8. Check for and lag any pipe you can feel warmth coming off.If you can feel heat radiating from a pipe, that heat is being lost. It is a simple and reliable test.

Tips

• Do this before winter rather than during it. Lagging also substantially reduces the risk of pipes freezing and bursting.
• Outdoor taps and their supply pipes are worth insulating and isolating in autumn — a burst outside tap floods into the wall.
• Modern cylinders come pre-insulated with foam. If yours is bare copper, a jacket is one of the best-value purchases available.

Common mistakes

• Leaving gaps at bends and valves — Heat escapes through the gaps and pipes can still freeze at the uncovered points. Fit it continuously.
• Insulating the ceiling directly under a loft water tank — It cuts off the warmth from below that stops the tank freezing. Insulate the tank itself and leave that patch of ceiling clear.
• Buying lagging without checking pipe size — Loose lagging insulates poorly and falls off; tight lagging will not fit at all.

Questions people ask