Insulating Pipes and Heating Ducts

Insulating pipes and heating ducts can save you money and conserve energy.
October/November 1991
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One of the most cost-effective and energy-conserving measures you can take is to insulate duct or pipe runs in the unheated areas of your home. By not insulating these conduits, you are essentially delivering heat that you've paid for to areas of your house you never use. One very important note: Never place duct or pipe insulation within 3 feet of the heating system, exhaust flues, or any other high temperature areas.

To insulate, install vinyl or foil-backed fiberglass duct insulation to all heating system supply ducts. You can also use regular-faced fiberglass insulation, which is less expensive and has a higher R-value (a measure of the ability to retard heat flow; the higher the number, the better the insulation). To determine how much insulation you need, first measure the distance around each section of duct and multiply that by the total length. Order about 30 percent more than the amount calculated to account for the overlaps needed for fastening.

Before you insulate, be sure to seal all air leaks in the system with duct tape and/or a high-temperature caulk such as silicone. Then, cover the supply ducts with insulation and secure it using clinch-type staples (preferred), wire or tape. Although not as long-lasting as staples, duct tape is easier to install. The tape should be wrapped completely around the duct and overlapped. The backing of the insulation must be on the outside surface. Exposed fiberglass and all joints between pieces of insulation should be covered with tape.

Damper control handles must be left in an accessible and operable position. Any labels on the ducts should be transferred to the outside of the insulation. Do not insulate your return ducts.

To insulate your pipes, follow these rules:

  • For hot-water systems, install “electrometric” or urethane rubber pipe insulation with a suggested minimum R-value of 6 — only on supply pipe. This insulation may not be used in applications where the temperature of the pipe exceeds 200 degrees Fahrenheit (such as on steam pipes).
  • For steam systems, install molded fiberglass pipe insulation with a minimum recommended R-value of 6 on all supply pipes. Before you purchase the insulation, carefully measure the outside diameter and lengths required. Remember to add a little for waste at joints.
  • Before installation, check for leaks in the system. If you find any, repair it before you proceed.
  • To install, place pipe insulation over the pipes, and seal with glue, duct tape or appropriate fasteners. Exposed ends of insulation sections at joints should be tightly scaled to eliminate air flow beneath the insulation.

To save even more energy around the house, try these do-it-yourself projects:

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