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Insulating Pipes and Ducts



When insulating attics, floors over unheated basements, or crawl spaces, be sure to insulate the pipes and heating ducts located in these areas, too. Ducts are the rectangular or cylindrical sheet metal passageways that carry heat from the furnace to your rooms. Unless they are insulated, they can waste much more heat than they deliver. Water pipes can be protected from freezing and heat loss with insulation.

To Insulate Pipes and Ducts, You'll Need:
  • Protective Gear, as described on page 5: Wear loose-fitting clothing, cotton gloves, and knee pads. A respirator and goggles can be helpful.
  • Insulation and Materials

    Note: Before purchasing pipe or duct insulation, measure the clearance around the fixtures. Some ducts are set too close to walls, etc., to allow space for the thicker R-11 insulation. Use the highest R-value practical in these cases.
  • Regular R-11 batt insulation. Rolls of special R-11 duct insulation are also available. Faced insulation should be used wherever people will come into routine contact with the ducts and on all air conditioning ducts.
  • Duct tape
  • For pipes, a minimum of R-3 "preformed" pipe insulation or R-7 batt insulation. (More insulation may be needed in areas with severe winter climates. Check with your utility for recommendation.) Use the preformed insulation made specially for pipes which comes in "sleeve" form.


Tools and Equipment:
  • Portable light and extension cords
  • Sharp knife
  • Measuring tape
  • Screwdriver, scraper, or abrasive material to clean pipes of rust and dirt


Insulating Heating and Air Conditioning Ducts
Securely tape any cracks or gaps and all joints in the ductwork with duct tape before you install insulation. Up to 30 percent of furnace heat is lost through cracks and seams in the duct work. Check to make sure that joints are securely joined (fasten any loose joints with screws) and that the metal or wire supports joining the ducts to the structure are in good repair.

For rectangular ducts, cut sections to a length equal to the circumference of the duct. Wrap the lengths around the duct (Fig. 5.1), taping them securely along their entire length. Tape the ends and edges of adjoining blankets together along their entire seam.

Figure 5.1
If the duct is recessed between joists, cut the pieces long enough to wrap as completely as possible, and staple the ends to the joists. (Fig. 5.2.) At the end of the duct, cut and fold the blanket as shown in Fig. 5.3.

Figure 5.2 Figure 5.3
When attic insulation is deep enough to cover the bottom of the heating ducts, batt insulation need only be installed on the exposed portions of the duct top and sides.

Insulating Pipes
Insulating hot water pipes not enclosed by floor insulation helps minimize heat loss. In the winter, it will help keep cold water pipes from freezing. If you live in a severe climate, consult your utility to find out whether greater pipe insulation R-values are recommended for your area.

Before installing pipe insulation, clean dirt and rust from pipe.
If you use pipe insulating "sleeves", apply them according to manufacturer's directions. (Fig. 5.4.) Apply batt insulation by wrapping pipes in a spiral fashion, overlapping each successive layer by half (Fig. 5.5). Wrap the insulation as loosely as possible; compressing it reduces the R-value.

Figure 5.4 Figure 5.5
Attach the insulation with tape, or with plastic or wire ties. If you use tape, apply it along every slit and around each joint between separate pieces of material, or attach it with plastic ties 1 inch from either end of the insulation and every 9 inches along the length of the pipe.

Next: Insulating Finished and Unfinished Walls


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