A Greener Home - BALTIMORE

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HVAC Ductwork

A forced air system delivering heat and air conditioning is one of the most common ways of conditioning the air in your home. A forced air system requires an air handler and a system of air supply ducts throughout the conditioned area of your home. This system will typically have a main trunk line and a network of branch lines to distribute air to individual rooms. This type of HVAC delivery also requires a return air network to the air handler. Just as the supply has a main trunk line with branches to insure proper distribution, so does the return network which returns air through a similar network of trunk and branch lines.

The technical details of an HVAC ductwork system can overwhelm you as a homeowner. To keep things as simple as possible, we recommend viewing the system just as you would view the circulatory system of the human body. You need a properly sized pump (think “heart”). You need a well designed supply system (think “arteries”). You also need a well designed return system (think “veins”). If any of these systems are designed improperly, or if they don’t have the proper size and flow, you will have cold a warm areas in your home, just as you would develop cold and/or warm areas (usually extremities such as feet and hands) in your body.

The HVAC network of supply and return ducts and their proper installation are key to having a home with even and efficient air conditioning and heat distribution. First, there must a plan which insures the proper volume of supply and return throughout the house. A certified professional HVAC contractor should perform a system load calculation (referred to as a Manual D) which will provide exact flow guidelines for each room in your home. They should also peform an overall system load calculation (referred to as a Manual J) which will determine the necessary size of your HVAC unit(s). Second, it is extremely important to properly assemble the system. No longer are segments of sheet metal ductwork simply banded together. In an energy efficient home today a mastic (adhesive resin) taped or painted joint to inhibit air leakage should be applied at all connection points. Ductwork should also be insulated in all unconditioned areas as well (most commonly the in basement area) to R5 or higher.

Since basement insulation is typically found on the exterior basement walls, this actually makes the basement somewhat of a “semi-conditioned area”, as opposed to an attic being completely unconditioned if insulated just above the ceiling drywall. HVAC ductwork applications should be avoided, if possible, in completely unconditioned areas, since they will be far less efficient. As a matter of fact, in most cases Energy Star guidelines do not allow HVAC ductwork to be run in unconditioned areas.

Another good building practice is the use of a duct pressurization system test prior to drywall installation. This procedure will determine if there are any leaks reducing air flow and efficiency. By performing this test prior to drywall installation, residual leakage can easily be remedied.

When building a new home or renovating an older one, make sure your HVAC contractor has properly sized your equipment and devised a ductwork network system that will provide the most efficient distribution possible. By constructing a network of ducts that are sealed at all connections and not leaking air, you are taking a major step toward maximum energy efficiency.

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