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HVAC Duct Systems - Ductwork systems channel the air to the spaces where it is needed from the air handler. HVAC duct systems also will pull the air from the space and channels it back to the air handler where it needs to be conditioned. In some commercial applications, the area above the ceiling is considered the return duct. All the return air is channeled back to the air handler through the plenum where it is conditioned in the air handler. Part of the conditioning process is the air being passed through an air filter and then an exchanger like a coil or heat exchanger.
HVAC Duct Systems | Round Duct
Some of the best types of ductwork systems are round hard duct systems. Round duct systems allow better airflow with the least amount of turbulence. This allows the designed amount of airflow to reach the spaces with the least amount of work from the blower motor. That equates to energy savings and better comfort for the occupants. In square or rectangle duct systems turning vanes are used in all turns to reduce turbulence.
All ductwork systems require insulation. Ductwork typically runs through unconditioned spaces and the insulation serves three purposes. First, it reduces any noise from the air flowing through the duct system. Secondly, the duct insulation reduces heat loss or heat gain from the unconditioned space to the duct system or vice versa. Finally, in cooling applications, the air conditioning duct system typically operates below the dew point.
HVAC Duct Systems | Insulation
The ductwork insulation provides a vapor barrier which prevents the ductwork from sweating and causing problems associated with moisture. All this is important because it saves energy when you increase efficiency. In most cases, round hard ductwork is easier to assemble and build. If you are getting new ductwork it is a good idea to consider round hard ductwork.
Duct sealant should be used around the seams of the ductwork connections and the seams of the insulation. The sealant is like a paste and is painted on. It seals the seams where the ductwork is joined. When properly done it eliminates air leaks. After this process is done the insulation is applied to the outer part of the ductwork. The paste is then painted on the seams and joints of the insulation. This gives the ductwork a vapor barrier. The vapor barrier prevents the duct from sweating when the duct is located in an area that is not conditioned such as in a crawl space or attic.
Ductwork Codes
When properly installed a good HVAC contractor will go above and beyond what the codebooks state in order to do a good job for the benefit of the customer. However, some contractors cut corners and often barely pass their code inspections. I’ve never been on the inspection side except working in commissioning but I have worked for many contractors and know they often cut corners to save time. Sometimes the code inspector will catch this and sometimes they will not. FYI, code inspectors cut corners too.
The code for ductwork can be extensive and this is simply a summary of what is very important for the proper installation of your ductwork. Here is a bullet point of basic (common sense) codes for ductwork:
- Ductwork shall not be sized less than the design operating pressure of the HVAC system. *Some contractors never check the sizing of the ductwork when they sell you a new system.
- Ducts should be properly supported and not block access to the spaces where they are installed. Additionally, ducts should not touch the ground.
- If you live in an area prone to earthquakes seismic codes will apply.
- If you live in a flood zone special codes will apply for the construction of the ductwork.
- If you have a furnace special precautions are needed to handle the higher temperatures near the furnace.
- Restrictions for the length of flexible ducting such as 5 foot limit on length and cannot be used as elbows.
- As noted above, the ductwork should be sealed. Most code authorities use SMACNA guidelines for this requirement.
As you can see, there are many important factors in HVAC ductwork including complying with codes. Usually, if they enforcing a particular code there is a good reason why they are doing it. By doing things up to code and the correct way you can add longevity and efficiency to your system,.
HVAC Duct Systems – Round Hard Duct Work
Technical Resource: Refrigeration and Air Conditioning Technology
