Venting permits the flow of air into and out of your home. The network of rectangular, round, and oval ducts that branch through the walls, floors and ceiling are designed to continuously control the humidity, freshness, and comfort level of the air in your home. Properly connected and insulated, the ducts in your home can provide significant levels of comfort as well as energy efficiencies that can lower your heating and cooling costs. This guide will help you understand how venting works in your home, and offer solutions to help you get the most out of your venting system.


The 3 Types of Venting
There are three types of venting in your home:

• Supply Air - A mixture of recirculated and outside air which has been conditioned and delivered into your home. This can be 100% recirculated air, or 100% 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.
  
  

The effectiveness of these venting systems is facilitated by a combination of heating and air system materials, duct sizes, duct sealant and insulation.

Duct Materials
Advances in the materials used in ductwork have resulted in ducts that offer improved temperature control, energy conservation and reduced condensation. 

Refer to the table below for information about common duct materials and their features.

Duct and Vent Sizes
While thousands of ducts in varying sizes are used for venting in different areas of the country, the table below shows the most common sizes and dimensions for ducts, in-wall stacks and registers. Sizes in color indicate the most commonly used dimensions.

Insulating Ducts
Insulating ducts in unconditioned spaces increases energy efficiency, saving you money in heating and cooling costs. It also prevents condensation from forming and reduces problems associated with mold and mildew. Fiberglass is the most commonly used insulating material.

• 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

Refer to the table below for information about various types of duct insulation.

R-Value
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 2.5” and provide an R-value of about R-4.0 per inch of thickness. Insulating your ducts can be a simple project for the do-it-yourselfer. Sheets are cut to fit and attached to one another with high quality foil tape or other attachment mechanisms. 

Refer to the table below for recommended R-values for insulation in unconditioned areas appropriate to your climate.

Duct Leaks
Studies show that conditioned air leaking from ducts typically losing an average of 20 to 30% of the air that moves through, raising a home’s heating and cooling costs by 20 to 40%.  Leaky ducts can also contribute to health issues, distributing contaminants like household and garden chemicals, insulation particles and dust throughout the home.

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 and 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 your local The Home Depot for a FREE in-home consultation.

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, it also makes the system run more efficiently, which translates into lower utility bills. While a well-designed system shouldn’t 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 to reach the heating or cooling comfort desired.

Cleaning Ducts
Cleaning air ducts periodically removes allergens like pollen as well as other contaminants like dust and dirt. You should consider having your air ducts cleaned 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. It’s a good idea to check debris accumulation in your ducts at least once a year.