What Are Duct Systems?

HVAC duct systems are forced-air processes that use ducts to distribute conditioned air throughout the dwelling. Air pressure and the degree to which this air is forced through the ductwork must remain as constant as possible to provide adequate airflow to all areas of the house. Supply ducts distribute air that’s been cooled or heated throughout the home. Return ducts take air back to the furnace of the AC unit to be reconditioned and recirculated. Duct sealing is important for indoor air quality.

Generally speaking, a house can have as much as a 30% loss of air as it escapes through leaks, holes, and poorly connected ducts.

You might have leaks in the ductwork of your home if you are experiencing any of the following:

  • There are tangled or kinked flexible ducts in your system.
  • You have stuffy rooms that are never comfortable.
  • You have rooms that are hard to heat or cool.
  • You have high summer and winter energy bills.
  • Your ducts are located in an attic, crawlspace, or garage.

Sealing ducts is important for the efficient distribution of air and the use of the AC equipment that has been installed. If the airflow is blocked, impeded, or stopped altogether, then certain parts of the HVAC system will be overworked and wear out in a short period of time.

Why Do Ducts Leak?

Ducts leak because they may be poorly constructed. A duct system is made from sheet metal and held together with screws. Sheet metal is an excellent material for creating avenues through which air can pass. However, the joints, fittings, and seams are also excellent locations for air to escape. Add to this, the possibility your AC system is unbalanced and you can end up with high positive and/or negative pressure in the ducts.

Ducts may also leak because of less than professional installation, remodeling, or the lack of skill from workmen and homeowners alike. Seams and fittings can leak as materials settle into their natural position over time.

Ironically, one of the primary causes of air leaks is an individual will apply “duct tape” to the problem. That original roll of gray duct tape is good for a lot of things. But, it is not rated to be used on your HVAC ductwork! The adhesive gives way under constant fluctuations in temperature and it simply dries up over time.

Typical Problem and Inspection Areas

duct sealing

The first place to check for leaks has to be the supply and return side plenums. Then, you want to check the starting collars and all the fittings. Make sure you inspect any splices and termination points where the ducts connect to the supply registers. All accessible ductwork will have to be visually inspected for damage, wear and tear, and inadequate insulation. 

Look for disconnected or fallen air ducts. Remove a few diffusers and the return grill air filter. Inspect for debris and the possible accumulation of mold spores. Inspect the evaporator coil for debris and mold. If other components of the HVAC system are contaminated with mold and debris, then areas of the duct will be contaminated as well.

Duct Sealing

There are many types of sealants. Some of the most common types of sealants used in the building industry are silicone, acrylic, polysulphide, fire-resistant, waterproof, and epoxy. These materials may be presented to the public as liquids, solids, powders, or foam.

Mastic sealant is a sealant that is usually distributed as a thick glue or paste form. This form of sealant may be used to join two surfaces together or protect the area to which it is applied. This product stays flexible even after it has been cured. It is an ideal product for applying to materials that have some degree of movement. 

Mastic is particularly suited for use with wood, glass, aluminum, concrete, marble, steel, and duct board. It is used extensively and successfully with ductwork in the high-velocity heating and air conditioning field. It contains heat-resistant properties and can seal and form itself to the surface at hand.

Why is Ductwork Important?

The heart of your home’s HVAC system is the equipment selected to deliver conditioned air – your furnace, air conditioner, heat pump, or boiler. However, as with the human body, a healthy heart cannot overcome problems associated with dysfunctional arteries.

Ductwork is the artery component of your HVAC system, channeling warm or cool air to various parts of the home as needed. When something goes wrong with an HVAC system, most people are inclined to think it’s a “heart problem” originating with the equipment. 

Frequently our trained technicians pinpoint a ductwork issue as the cause.

Damage, Sizing, and Poor Installation

Ductwork that is damaged, poorly sized, or improperly installed can result in bad airflow, leaks, and excessive utility bills. Our technicians can usually repair damaged ductwork without too much trouble. The problem is when they encounter poor performance due to poorly sized ductwork or sloppy installation.

Over-sized systems run up utility bills and have trouble maintaining the desired airflow. Under-sized ductwork causes noise and strain on the system, leading to premature failure.

Sizing ductwork involves calculations that take into account the local climate, size of your home, type of construction, insulation, windows and doors, shading, and other factors. Incompetent or lazy contractors may ignore the guidelines and simply design ductwork by “feel” based on their experience. Often their “feel” involves cutting corners for the sake of a lower bid price. 

How would you like to employ a heart surgeon with that attitude?

A key measurement when sizing HVAC systems is CFM, i.e., how many cubic feet per minute of air movement the system will be required to handle. A common mistake made by some contractors who install combined heating/cooling systems is to size the system based on the heating load. Air conditioning requires more CFM, so when the same ductwork is used for both heating and cooling it’s wise to size the system for the air conditioning.

Zoning Issues

Another problem we frequently encounter is when homes are not properly zoned. Zoning refers to different rooms or areas with different airflow requirements for maximum comfort and efficiency. Some single-story homes can get by with a single HVAC zone, but most homes with two or more floors will need separate ductwork zones for each floor. That’s because hot air rises while cool air sinks. 

So a single zone in a multi-story house usually will result in uncomfortable temperature variations. The upstairs will be much warmer than the downstairs. This is a common occurrence and one you’ve probably encountered either as a homeowner or a visitor to a home with poor zoning.

All of this points to the importance of selecting an HVAC contractor that operates professionally and follows the field’s codes, standards, and best practices.

Competitive bidding often puts pressure on contractors to cut corners in ways that impact system performance. Just keep in mind that homeowners who ignore best practices in favor of a cheaper price always end up paying a bigger price down the road.

Freedom Heating and Cooling is professionally prepared and stands ready to inspect and repair your ductwork. A complete professional inspection of your HVAC system can reduce your energy consumption and assist you to become eligible for the many federal and state programs available to gain energy tax and income credits.


A professional HVAC service person can perform leak testing using a duct blower door test. This and other tests can show where and how much air is being lost through the ducts. That same professional can make recommendations for the maintenance and repair of areas that need repair/replacement.

Also, an inspection done by a professional may reveal if you qualify for energy efficiency credits with Alabama Power or other rebates through the federal government.

For a complete inspection of your HVAC system, call Freedom Heating and Cooling at 205-444-4444 or visit our duct services page.