If you’ve been shopping for a new furnace or A/C for your Mid-Atlantic home, you’ve seen how advanced features play a major role in HVAC efficiency, comfort and ROI. The heating and cooling systems certainly are the heart of the HVAC system, but consider that the air ducts are the lungs. If you want better comfort, performance and more energy dollars in your pocketbook, get to know your ductwork and how ductwork design contributes to HVAC efficiency and performance.
Inside the Envelope, Please
The efficiency of your heating and cooling systems depend on good ductwork design. A high AFUE and SEER won’t amount to much except high energy bills if the ducts are leaky, incorrect size or possess some other design flaw.
Since the ductwork conveys heated and cooled air to living spaces, the ducts are essentially an element of the home’s envelope and should be installed inside the conditioned areas. This ensures that any air leaks or insulation deficiencies won’t be warming or cooling the basement or attic.
Sealed chases, hang ceilings and raised floors are ideal locations for ducts. Keep in mind, however, that if any portions of ductwork are located outside the conditioned areas, they should be insulated to prevent heat gain/loss.
It’s the Journey
Modern building engineering dictates that permanent and approved materials be used for ductwork fabrication. One of the most common materials used is sheet metal. Metal ducts are available insulated or uninsulated and require specific sealing materials, such as mastic paste, metal tape and screws. Another type of ductwork that’s becoming more popular is round fiberglass flex ducts. Flex ducts offer the advantage, as the name states, of being flexible for smooth and seamless turns.
If you live in an older home and you’re upgrading your heating or cooling system, it’s important to have your HVAC technician inspect the ductwork for compatibility and design. In older homes, sometimes building cavities inside the walls, floors and attic are used to channel airflow. This is bad building science, and it likely shows in your high energy bills and indoor air quality (IAQ). Since air is conveyed in building cavities, there’s very little control over IAQ, and harmful contaminants can more readily make it to the living spaces.
Ducts, Dampers and Airflow
Duct dampers are used to regulate the amount of airflow to each register. Dampers are an important tool for your HVAC technician so that he or she may balance airflow evenly throughout the home. Dampers should be installed at the trunk and runout joint. If dampers are installed near the register, airflow backs up inside runouts, which is technically a blockage.
Balanced Air Streams: Supply and Return
An HVAC system can’t deliver peak efficiency without balanced air supply and return. Unbalanced air supply and return contradicts the goal of a forced-air HVAC system to provide heated and cooled airflow for maximum comfort and minimal energy costs. Following are the basics:
- The thermostat signals the heating or cooling system to activate.
- The furnace blower pulls air from the living spaces into return grilles, air filters and return ducts.
- Airflow is pulled across or through the heat exchanger to be heated or cooled.
- The blower forces the conditioned air through supply ducts.
- The conditioned air enters the living spaces through registers.
If there’s an obstruction in this process, and there could be many, comfort suffers, HVAC wear increases and your energy bills go up. Therefore, to balance air supply and return, good ductwork design dictates a return grille in each area there is a supply register.
Sized, Sealed and Delivered
Correct duct sizing is equally important to correct furnace or A/C sizing. Ducts that are too small are going to make a lot of noise and create unbalanced airflow. Energy bills go up because the blower must work harder to force air through supply ducts that are too restrictive. Ducts should be sized using Manual D from the Air Conditioning Contractors of America (ACCA).
Duct sealing is a critical juncture in ductwork design. It’s not uncommon for poorly sealed duct joints to fail and separate after only a few years and send your heated and cooled airflow into the basement or attic. Once ducts are sealed using accepted products for the duct material, duct air tightness is measured using a blower door test.
Learn more about quality ductwork design available from the pros at Griffith Energy Services, or contact us today at 888-474-3391 to schedule an appointment!
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