Don't overlook heater, duct insulation


November 20, 1993|By Gene Austin | Gene Austin,Knight-Ridder News Service

Most homeowners are aware of the importance of insulation in attics, walls and floors, but they sometimes overlook other items, such as water heaters and metal furnace ducts, where insulation can cut energy costs.

Both electric or gas water heaters can be insulated to reduce heat loss through the tank walls, reducing the need to reheat the water in the tank.

In general, insulating older water heaters pays off best, since newer heaters often contain effective built-in insulation.

To test a heater, feel the side of the tank several times at intervals during a day. If the tank is more than slightly warm, it should benefit from added insulation.

Kits to insulate water heaters are available at some home centers for less than $20. The kits generally contain a blanket of fiberglass insulation, sized to fit typical heaters, plus instructions and tape to hold the insulation together at joints.

Fiberglass wall insulation or duct insulation with foil facing, sold in rolls, can also be used to insulate water heaters.

Both types of insulation are available at some home centers and building-supply dealers. Most wall insulation is 3 1/2 inches thick and about 15 inches wide; duct insulation is usually 1 1/2 to 2 inches thick and is made in various widths.

Insulation with a kraft-paper facing should not be used for water heaters or ducts since the paper is flammable.

When installing fiberglass insulation on either water heaters or ducts, the facing goes on the outside. Wear a dust-filter mask, goggles, gloves and other protective clothing to prevent skin discomfort and inhalation of the fiberglass particles.

Duct tape -- a widely sold, silver-colored fabric tape that is self-adhesive -- can be used to seal insulation joints, but in time it usually dries out and pulls loose. A better choice is aluminum-foil tape, a self-adhesive tape normally sold in 3-inch-wide rolls. A mail-order source of foil tape (about $13 for a 50-yard roll) is Improvements in Cleveland (telephone [800] 642-2112).

Vertical strips of insulation are generally used to wrap a water heater. Measure the height of the tank and cut strips to length with a utility knife and straightedge. Tack individual insulation strips in place with tape tabs. When the tank is covered, hold the insulation strips together at joints with continuous vertical strips of tape reinforced with horizontal strips of tape.

When insulating an electric water heater, make cutouts in the insulation for the small doors in the heater jacket. The doors give access to thermostats and heating elements. A panel of insulation, with cutouts for pipes, can be placed on top of an electric water heater.

On a gas water heater, keep insulation well away from the burner area. Do not insulate the top of a gas water heater.

Insulation is especially important on metal heat-supply ducts that run through unheated areas such as attics, crawl spaces and basements, where a significant amount of heat can be lost through duct walls.

Before insulating a duct, seal the joints of the duct sections. Joint sealing can be done with aluminum-foil tape, mentioned above, or a duct mastic and fiberglass tape. The mastic and fiberglass tapes is available from some heating-supply dealers; one source is the GRASP (Grass Roots Alliance for a Solar Pennsylvania) store at 3500 Lancaster Ave., Philadelphia ([215] 222-0318). Sealing duct joints with mastic and fiberglass tape is much like sealing wallboard joints. Spread mastic over the joint with a wide putty knife, embed the tape in the mastic and apply more mastic to cover the tape.

To insulate a duct, measure the length needed to surround the duct, cut a strip of insulation to fit, and wrap it around the duct. Fasten joints of the insulation strips together with aluminum-foil tape or duct tape.

Research by GRASP and several other groups has shown that the efficiency of an air-circulating heating system can often be improved by sealing joints of both heat-supply and return-air ducts, though it is not necessary to insulate all ducts.

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