How to Insulate
Water Pipes

Before you begin

  • Check pipes before insulating. Don't insulate until any leaks are repaired and pipes are properly supported.

  • To be effective, insulation must touch the pipe. Gaps between the insulation and the pipe allow cold air to penetrate, which increases the chance of freezing.

  • Don't take short-cuts where insulation is difficult to install. Any spot that's left uncovered or inadequately covered could freeze.

Types of Pipe Insulation

Two types of pipe insulation are commonly used:

Unfaced fiberglass batts work well on pipes in areas such as attics and crawlspaces where people won't often be present. Tubular foam is a better choice for areas where people may be present. These areas would include garages, utility rooms and basements. Match the inside diameter (ID) of the insulation to the outside diameter (OD) of the pipe.

Spiral wrap tape, thin strips of fiberglass and "bubble" products are not acceptable because the insulating value is too low.

Minimum R-value requirements are listed below.

Tubular Foam

Slip straight sections into place on the pipe. The slit should face downward on horizontal runs. Cut the ends so that the pieces fit snugly, without gaps. At corners, cut the end of each piece at a 45 degree angle. Fill any gaps with wedges of foam insulation cut from a scrap.

Secure the insulation with one of these options:

  • Apply glue to the ends and the slit.

  • Wrap the insulation with foil tape, plastic twine, or rust-proof wire. Start 1 inch from the end and then circle the insulation every 9 inches. Place the last wrap 1 inch from the far end. Do not leave any areas of pipe exposed.


Use fiberglass for sections of pipe that can't be easily insulated with tubular foam. The fiberglass should touch all parts of the pipe.

Apply the insulation in one of these ways:

Cut the insulation into long strips wide enough to wrap around the pipe with a 3 inch overlap. Place the insulation lengthwise on the pipe.

Wrap the insulation around the pipe in a spiral. Overlap each turn by 1 to 3 inches.

Secure insulation every 12 inches with twine, wire ties, plastic straps or approved tape at least 1 inch wide. Don't compress the insulation more than 1/2 inch, because that reduces its insulating value.

Water Heater Connections

Pipes leading to a water heater (both hot and cold) should be insulated to reduce heat loss from the tank. If the water heater is in a conditioned space, insulate the first five feet. Tubular foam insulation is a good choice for straight pipes. For flexible connectors, use scraps of vinyl-faced duct wrap or water heater wrap with a Flame Spread of 25 or less.

Where to Insulate

All water pipes in unheated spaces, such as crawlspaces, garages, and attics, must be insulated to prevent them from freezing. Don't overlook pipes that serve refrigerator icemakers, undersink water heaters and other appliances. Do not insulate drain pipes, pressure relief valves or natural gas pipe. Leave the handles of shut-off valves exposed.

Pipes in floors or attics don't need more insulation, if they are covered by at least 3 in. of cavity insulation, such as cellulose or fiberglass.

Copyright 1993 Iris Communications, Inc.

Source: Oikos

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