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Duct Design Makes a Significant Impact on Your Home’s Heating and Cooling System

If your home has a central furnace, air conditioner, or other HVAC appliance, your ductwork is an unsung hero in your home. Good duct design determines how comfortable your home is and how well the temperature is managed throughout the house. Moreover, it  has a huge impact on your home's energy use. The average homeowner can attribute half of his or her energy bill to heating and cooling costs, with almost 30 percent of that energy being wasted due to duct damage.

In this article, you'll learn about the role of ductwork in your Chicago area home, ductwork design considerations, and how to maintain your ducts over the life of your HVAC installation.

What is the purpose of Ductwork?

If you have a fireplace in your home, you know that it can be a cozy place to congregate on winter evenings – but you have to gather close by to enjoy its warmth. Furnaces don't conjure up nearly as many cozy feelings, but they do keep your whole house warm thanks to the hidden ductwork. 

Ducts are the circulatory system of your home. Good duct design ensures that every room in your house receives an appropriate amount of conditioned air, whether warmed or cooled. They also bring stale air in from the various parts of your home and route it through the central heating or cooling equipment, which may include filtration systems, air cleaners, as well as humidifiers or dehumidifiers.

Duct design is usually implemented when the building is first constructed, but may require significant remodeling later. It's very important for homeowners to care for, maintain, and upgrade ducts for substantial cost savings over time.

What Is Good Duct Design?

Ducts are differentiated by two roles: supply ducts, which deliver air to your living areas, and return ducts, which bring old circulating air back to the central HVAC system. Each type can be installed in a variety of designs.

 For return ducts, there are two general installation plans:

  • Central return systems have a single intake that feeds back to the central HVAC appliances, and rely on the outward pressure of the supply ducts to displace old air. These systems often suffer inefficiencies at cycling air, especially when rooms are closed.
  • Multiple-room return systems, by contrast, have return vents in all or most rooms in the house, so that old air is constantly being pulled out as new air is being fed in.

Supply ducts have a number of different basic schemas, which vary in effectiveness based on the design of the house:

  • Trunk and branch systems, among the most popular duct designs, have a single large "trunk" duct leading out from the central air handler, and smaller ducts which branch off from the trunk and lead directly to each room.
  • Radial systems, another popular design, has no main supply lines from which smaller, feeder lines take their air; they simply run ducts directly out from the central HVAC unit to each room.
  • Spider systems, which can be seen as a middle-ground between trunk and branch systems and radial systems, run a number of larger supply ducts to mixing boxes in various parts of the home. From there, smaller branch ducts can distribute the air to individual vents.
  • Perimeter loop systems have a loop of duct that circles the home, supplying air to various vents. This loop is fed by a number of supply ducts from the central unit. These are fairly rare, generally only found in homes with a slab foundation, in colder climates.

It's important to consider that many homes are built without a great deal of consideration to their duct design, for reasons of cost or expediency. Houses that are able to keep their ductwork inside the conditioned parts of the house – in dropped ceilings, for example, or between the floors of multi-story homes – have some resilience against efficiency loss due to age and damage, because leaks in the ductwork generally still feed conditioned air into living areas.

Some duct systems use the structure of the house itself as a guide to duct design, with ductwork that passes through building cavities, panned floor joists, crawlspaces, wall stud spaces and closets. While these may be inexpensive to install, this duct design doesn't lend itself well to maintenance, and often sacrifices optimal air distribution.

The material of the ductwork can also impact duct performance. Available duct materials include:

  • Sheet metal, the most common duct material, which offers a low resistance to airflow but no natural insulation. Sheet metal ducts must also be installed and sealed carefully, as leakage is a danger at every seam, connection and joint. Sheet metal ductwork can also transmit an undesirable amount of sound.
  • Fiberglass duct board, which comes pre-sealed and pre-insulated from its manufacturing process. Fiberglass duct board offers a high degree of sound reduction, but if it's not installed properly, it can suffer damage due to age much more quickly than sheet metal ducts.
  • Flexible nonmetallic ducts are simply duct liners given shape by an inner coil of wire. Flex ducts are commonly used as return air ducts, and can be used as connectors, but they are also more susceptible to damage.

All ducts should be sealed to ensure that air reliably gets to its intended living spaces, and insulated to prevent heat gain or loss in transit. If ductwork passes through non-conditioned areas or external walls, the amount of insulation should be increased.

Because warm air rises, solar heat gain is concentrated on exposed roofs, and multi-story homes often have different heating and cooling requirements on upper levels than on lower ones. Duct design alone may not be enough to ensure that all areas of the home remain cool or warm. If you own a multi-story home, you may want to consider having a separate HVAC installation for the top floors.

How Do You Take Care of Ducts?

Ducts, like the rest of your HVAC installation, should undergo annual inspection and maintenance. Beyond that, there are some guidelines you can follow to make sure you're getting the most out of your system:

  • If you're not getting the needed airflow there may be leaks or obstructions in the system. Look over your ducts for tears, loose joints and holes, especially near vents. Streaks of dust radiating outward from the ducts can also indicate a leak. Leaks should be repaired by a professional. Contact your local HVAC specialists if you suspect any damage.
  • It may sound strange, but you shouldn't use duct tape on ducts. The adhesive used in duct tape is a short-lived, rubber-based adhesive, and doesn't perform well when exposed to extreme temperatures. At best, it's a short-term stopgap repair. If you see duct tape on any of your existing ducts, inspect the duct at that location.
  • Keep an eye out for any damaged or missing insulation on your ducts, and if you find any, remember to check the underlying ductwork for damage.
  • Keep vents clean and unobstructed. No matter how good your duct design is, it won't help if it's blowing out conditioned air straight into the back of a bookshelf or the underside of a couch.
  • Consider improvements to your home air cleaning system. Advanced filters can reduce dust buildup inside the ductwork, and UV light filtration can impede mold and mildew growth. Not only will this improve your indoor air quality, but it can reduce the chance of duct and vent obstruction.
  • Have your ducts cleaned. Not only will this clear out any large obstructions – air filters that have been sucked into the ductwork, small animals that have found their way in – but it will keep any dust buildup from cycling back into your air. Commission a duct inspection by a reliable HVAC technician. It's not uncommon for unscrupulous contractors to persuade homeowners they need a duct cleaning when it's not really necessary.
  • Schedule a duct blower test with an HVAC professional. This test will determine the pressure in your dust system, and can indicate whether air is being distributed throughout your home as it should be.

Need More Information?

Duct design can be a complicated subject, but in Chicago's climate it's paramount for your home comfort. To learn more, or to schedule tests or upgrades, don't hesitate to contact us atComfort24-7.com.

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