Avoid common HVAC installation mistakes

With a properly sized HVAC system, the temperature can be set as high as 76 or 78 degrees, and the home still feels comfortable

The first of three HVAC installation mistakes contractors typically make is oversizing the HVAC system.

Oversizing is one of the most common HVAC installation mistakes

The rule of thumb of 1 ton for every 500 square feet of conditioned space is outdated. In reality, 1 ton can condition 1,000 or more square feet. The best way to accurately determine the right size of the system needed is to use a load calculation program such as Manual J.

Oversizing a system has many consequences. A larger system costs more money to purchase and install. In the long run, it also costs the customer more money because it runs for a short period of time and shuts off. This short cycling uses more energy and raises energy bills.

Another problem with oversized systems is that they don’t run long enough to dehumidify the home properly. Increased humidity can make the home feel uncomfortable; as a result, a homeowner will often set the thermostat much lower.

With a properly sized HVAC system, the temperature can be set as high as 76 or 78 degrees, and the home still feels comfortable.

The goal is to correctly size the HVAC system so that it runs slow and steady, and runs constantly during the hottest days.

The better the seal, the less likely air will escape from the ducts into areas such as the attic.

Improperly sealing ducts

Not sealing ducts correctly is other of the most common HVAC installation mistakles. The better the seal, the less likely air will escape from the ducts into areas such as the attic.

Mastic or mastic tape is the best choice, and it must be applied to all duct connections – metal to metal, flex liner to metal, and ductboard to metal.  Some contractors seal only the insulation around the ducts, with tape or even mastic, failing to tape the ducts. This doesn’t properly seal the ducts and leads to excessive leakage.

Even when they use the right materials, contractors don’t always seal ducts correctly. It’s important to tightly seal the HVAC boots to floors and drywall, and toe kick ducts should be avoided altogether as they are very hard to seal to the cabinet and are often damaged during cabinet installation, leading to excessive leakage.

Air leakage can cause other problems besides inefficiency. Air escaping into attics and crawl spaces can cause those areas to become over pressurized. As a result, dust and dirt get pushed into the rest of the house.

Location of ducts

The location of ducts is very important, and it’s best to keep them inside the conditioned space. A duct placed in an unconditioned space, such as an attic, has to work harder. Unconditioned spaces deal with extreme temperatures, and, even when insulated, the duct is not fully protected from these extremes.

If contractors fail to leave space for air ducts in additions, ducts get compressed and forced into spaces that are too small. This restricts airflow.

The best placement for ducts is in the middle of the house pointing toward the outside. Positioning ducts this way allows for the fewest compressions and turns.

Air moves most easily through straight ducts, allowing for a smaller system, and the most efficient and comfortable heating and cooling.

−By Carl Seville with Rebecca Torchia

Carl Seville is a long-time remodeler and a principal with SK Collaborative, a Georgia-based consulting firm that helps remodelers and builders make homes more energy efficient. Seville provided these expert tips during a recent Pro Construction Guide PROcast, a podcast just for pros.