Buying Guide

Types of Vents

Venting Types

There are three types of venting in your home: venting for supply air, return air and exhaust air. The effectiveness of these venting systems is facilitated by a combination of heating and air system materials, duct sizes, duct sealant and insulation.

Supply Air: A mixture of recirculated and outside air which has been conditioned and delivered into your home. This can be either 100 percent recirculated air, 100 percent outside air or any mixture of the two.

Return Air: Air that has circulated through your home as supply air and is returned to the HVAC system for additional conditioning or release from the home. Return ducts help pull air into vents that is being pushed in by supply ducts.

Exhaust Air: Air that is removed from a space and not returned, removing airborne impurities, like smoke from cooking or moisture from bathrooms and washing machines. This keeps the air clean and prevents damage from excess moisture and dust.

Duct Design

Ducts can be made from galvanized steel, fiberglass duct board/insulation panels or flexible ducting. They are available in a range of sizes but ducts, in-wall stacks and registers have standard sizes commonly found in homes.

metal ducts
plenums & air returns
flexible ductwork
Description Galvanized steel Fiberglass duct board / Insulation panels Flexible ducting
Feature/Benefits Cuts and bends easily Can be wrapped or lined with fiberglass insulation Constructed with built-in thermal insulation Dampens sound Can be cut into various shapes with special tools Round and covered with thin layer of plastic over fiberglass insulation Connects supply outlets to rigid ductwork Works best with minimized turns and in lengths of 15 feet or less
Common Duct and Vent Sizes

Ducts: 4, 5, 6, 7 or 8 inches

In-wall stacks: 3.25 x 10 inches, 3.25 x 12 inches or 3.24 x 14 inches

Registers: 4 x 10 inches, 6 x 10 inches, 4 x 12 inches, 6 x 12 inches

Insulation & R-Values

Insulating ducts in unconditioned spaces increases energy efficiency and prevents condensation from forming so you can avoid problems with mold and mildew.

Return air ducts only need to be insulated if they pass through environments that adversely affect the return air temperature.

Supply air ducts don’t require insulation if they run exposed through the space being conditioned.

Exhaust air ducts normally do not need insulation.

Insulating your ducts can be a simple project for DIYers. Sheets are cut to fit and attached to one another with high-quality foil tape or other attachment mechanisms.

Insulation Type


  • Shorter lengths
  • Available for various elbow and tee joints
  • The most commonly used insulating material

Self-adhesive foam insulation with aluminum foil backing

  • Effective where space is at a premium
  • Suitable for hot and cold pipes

6-foot lengths of 3/8-inch tubular polyethylene foam

  • For use with long runs of pipe
  • Pre-slit tubes come in different internal diameters
  • Tubes snap into place quickly and easily on pipes from ¼-inch iron to 1¼-inch copper
  • Available as rubber tubes

Spray foam

  • Used for new installations
  • Used for spot repairs and leak sealing

Duct insulation is measured in terms of R-value, which is a measure of resistance to heat flow.

The higher the R value, the better the degree of insulation.

Duct insulation ranges in thickness from 1 to 2 ½ inches and provide an R-value of about R-4.0 per inch of thickness.

Warm Climate

  • R-Values for Unconditioned Attic: R-4 to R-8
  • R-Values for Unconditioned Basement/Crawlspace: None to R-4

Mixed Climate

  • R-Values for Unconditioned Attic: R-4 to R-8
  • R-Values for Unconditioned Basement/Crawlspace: R-2 to R-8

Cold Climate

  • R-Values for Unconditioned Attic: R-6 to R-11
  • R-Values for Unconditioned Basement/Crawlspace:R-2 to R-11
Upkeep & Features

Leaky air ducts can raise a home’s heating and cooling costs by 20 percent to 40 percent, and can contribute to health issues. Keep an eye on duct leaks and clean the ducts if mold or excessive dust is present.

Duct Leaks

Look for air leaks in ductwork in unconditioned areas, like attics and crawlspaces.

Check for separation in areas where sections join and for obvious holes.

If your duct joints have been sealed with cloth duct tape, look for cracks and loose or peeling tape.

Small repairs are fairly easy to make, using duct mastic/sealant, mastic tape or high-quality duct tape approved for heating and air conditioning systems.

Bigger repairs may need to be made by a professional. Contact The Home Depot’s Installation Services for more information.

Maintaining a Balanced System

Forced air distribution systems are designed to be a closed, pressure-balanced loop, with the same amount of air entering and leaving conditioned zones through the ductwork. Maintaining a balanced air system not only makes your home more comfortable but also makes the system run more efficiently, which translates into lower utility bills.

While a well-designed system should not need adjusting, if you find some rooms too hot and others too cold, you can tweak the balance yourself by adjusting levers on air registers and balancing dampers in rooms.

Cleaning Ducts

Cleaning air ducts periodically removes allergens like pollen as well as other contaminants like dust and dirt. Check debris accumulation in your ducts at least once a year and have them cleaned immediately if:

Mold is visible

Ducts are infested with vermin

Ducts have excessive dust or dirt that is being released through supply registers 

Cleaning techniques range from using a brush, rag and vacuum cleaner to remove loose dirt and dust on registers, grilles and duct walls to professional whole-house duct cleaning services that clean the entire HVAC system with services like duct sealing and biocide applications.

Features to Consider

Decorative grilles and registers are available in a variety of materials and finishes and are an easy way to change your decor.

In-line booster fans boost heated and cooled air for increased comfort.

Register vent boosters pull more air from registers and increase comfort in rooms that aren’t served by your HVAC system.