How Do Ducts Work?
For those of you with a central air conditioning and/or heating system, ducts are what transport the hot or cold air throughout the home. To better understand the ductwork, it is best to look at some of the important components.
Duct Work – Furnace/Heater/Air Conditioner
Think of the system of ducts like a tree. The roots here are the heating/cooling system. All ductwork begins here.
Duct Work – Plenum Chamber
Plenum chambers are what connect the “roots” of the system to the trunk. They are also the central collection and distribution components of the system. The plenum
often has two parts. The first is the return plenum which carries and takes in the air from the return grill(s). The supply part directs air from the heating/cooling unit to the –
Duct Work – Main Supply Duct
Also known as a rectangular duct, this duct is given its name due to its shape, although it isn’t always a rectangle. These ducts are usually larger in size – 12 inches or more – and can also be known as trunk lines. This duct acts as the “trunk” of the system and sends the hot/cold air to the –
Duct Work – Supply Branches
These are the “branches” of the duct work system, usually one per room in the home, depending on its size, although larger rooms can have 2 or 3 supply lines feeding to it. These supply branches/duct work can be made of hard or flexible supply lines depending on the type of home and allowable space for ductwork. For example, in a home with an attic, a flexible line that looks like a giant silver hose can carry the air to various rooms. For homes without an attic or apartments, these ducts are usually hard and rectangular to accommodate the allowed size for ductwork.
Other components found in supply branches include stacks, or ducts that are installed vertically. These stacks are often connected to a boot, or stack boot, found at the end of the duct and act as a sort of joint between components. The two main types are end boots, which are parallel to the supply branch, and angle boots, which are at an angle to the supply branch. Connected to the one end of the boot is a head or stack head, which connects to the rest of the duct work. Connected to the other end of the boot is a register head, which connects the boot to the –
Duct Work – Air Terminals
These are what cap supply branches when blowing air. One of the most common are known as registers or grills, aka those rectangular vents about a foot wide where the cold or hot air blows. Many of these have slides that allow users to control the direction of the air flow, as well as shut so as not to cool or heat rooms not in use. Another common type of air terminal is the diffuser, usually a round device commonly used in conjunction with all-air and air-water HVAC systems.
Duct Work – Return Ducts
These ducts serve to help regulate your heating and cooling system by sending the hot or cold air back to the unit and the thermostat. When this air reaches a certain temperature the thermostat will switch off. These ducts are easily identifiable by the filter contained underneath the air terminal, commonly referred to as the return grill.
Duct Work – Return Air Drop
The return air drop is what takes the returned air and outdoor air and feeds it into the heating or cooling unit for conditioning and re-distribution. It is often “L” shaped.
Duct Work – Transitions
These are the “elbows” of the duct work system. They connect various components including from main supply to plenum, supply to branch ducts, from return air to air drop, etc. A common type of transition is called a rectangular side take-off. It is shaped like a lowercase “r”, with the horizontal curl attached to whatever component is being connected as well as the ability to continue the flow into other areas of the duct work. Another common type of transition is the rectangular vertical. These are shaped or curved like an uppercase “L” where the stem is the same size as the horizontal part. These transitions simply connect one component to the other.
Duct Work – Reducer
Notice that some of your registers are smaller than others? This is accomplished with the help of a reducer. This is a type of transition that shrinks the supply duct, and subsequently the supply branch, in smaller areas such as bedrooms and bathrooms.
Duct Work – Dampers
In more modern units, dampers are used to create or eliminate zones in the home that can be too hot or cold. A computer in the heating or cooling unit controls the dampers by opening and shutting them depending on the settings in your unit.
Duct Work – Filters
These are what keep your air clean. They catch dirt, dust, and other contaminants in your system and should be replaced regularly. However, there are several types to choose from.
1 Inch Filter
These have been the standard for most units for many years and are usually replaced a few times a year.
4 Inch Filter
Growing in popularity, these filters catch more contaminants than the standard one inch filters. However, they come with a heftier price tag.
Just as the name implies, these filters can be washed by hand and can save a great deal of cost. However, they also need to be replaced after so many washes and reuses.
Consult your owner’s manual on your heating or cooling system for which type of filter works best with your unit, along with what size it takes.
Other Important Facts About Duct Work
- As stated above, one of the best ways to maintain your entire HVAC system is to regularly replace the filter. A good tip is to write the date on the filter as you replace it to remind you of how long it’s been in there.
- Do not use filters in combination. Four 1 inch filters are not the same as one 4 inch filter.
- One of the main sources of dust in the home is carpeting. In addition to switching to hard floors or hypoallergenic carpeting materials, dust can be reduced by introducing more outside air into the home.
- Duct cleaning is not always necessary. According to the EPA, if no one in the home has allergies or unexplained symptoms and if no dirt is visible in your duct work, no cleaning is necessary.
- When cleaning is necessary, consider duct cleaning companies that are certified by the National Air Duct Cleaners Association. In order to get the certification, providers must pass certain courses and tests to ensure the quality of cleaning.
- Asking for references or doing an internet search on a duct cleaning company can also let you know who has a long standing reputation for good work.
- If possible, check your duct work for leaks. Leaks can be visibly identified or by going over the ducts when the fan is on to check for leaks by touch. Leaks happen most often at joints, elbows, or anywhere two components connect. These leaks can add up to huge costs in your energy bills.
- Do not use standard duct tape to seal leaks. It may have “duct” in its title, but not all tapes are created equal. Tape with the Underwriters Laboratories logo is specially designed for fixing duct leaks.
- UV light cleaners are an option more and more companies are offering. Certain studies (http://www.hpoe.org/resources/case-studies/1276) have shown UV light to be an actual eliminator of germs and other contaminants, but the functionality in the home remains to be seen.