Do you remember the old days when air-conditioners hung out of windows and were used to cool individual rooms? Maybe that wasn’t so long ago, but a major innovation that led to today’s central HVAC systems was the design and implementation of ductwork. The ductwork in your home carries the cool or warm air from the air-conditioner or the furnace to each room in your home. The ductwork also brings the “return” air through a filter and back to your HVAC system.

While you probably don’t spend much time thinking about the ductwork in your home it’s very important to the overall life of your HVAC system, the health and quality of the air in your home and the efficiency of your system.

These are some of the common problems with ductwork and the issues they can cause for comfort in your home.

Common Problems

Restriction in the Return

A restriction in the return can happen for a variety of reasons. It may be a poor initial design, an increase in the size of replacement system without also increasing the size of the return box or return ductwork, or it might simply be the failure of the homeowner to replace their filters.

There are several bad things that can happen from a restricted return. The first is a reduction in efficiency. The power required to move restricted air goes up exponentially and the blower motor will have to strain to move the air. This increases the use of power (loss of efficiency) and reduces it’s life as well as potentially other components in the system. In severe cases of restriction your coil can actually freeze up causing your system to stop cooling your home.

Restriction in the Supply

Restriction in the supply has less potential causes, but will create similar issues as a restriction in the return. Really the only probably causes for a restriction in the supply would be improper initial design, a malfunctioning or improperly designed zoning system, or too many closed supply registers in the home.

Air Leakage

Air leakage can happen for a variety of reasons, but the most common is an improperly attached duct. When ducts are installed they should be carefully attached, secured, and sealed on both ends. If ducts are not properly installed and sealed, they will lose some of the conditioned air that should be going into your home resulting in a loss of efficiency. If leaks exist in the return ducts you may be introducing additional humidity into your home. If you suspect duct leakage, a qualified contractor can inspect and seal all ducts that are accessible. 

Condensation Creating Mold/Mildew

Condensation, mold and mildew can be disconcerting when it appears in and around your ductwork or registers in your home. The way it happens is fairly innocuous and mold/mildew will grow in virtually any location where dust and moisture exist. The most common cause of mold/mildew in your ducts or on your registers (or even the ceiling around your registers) is increased humidity in your home, combined with very cold air coming from your A/C system. The metal registers in your home are cooled by the cold air coming from your air-conditioning system. While the fan is running condensation will be minimized due to the air movement, but once your system is turned off the ambient air in your house will be warmer than the register and will condense on the metal. The presence of this moisture will create mold/mildew to form. 

Poorly Balanced Temperature

When your home was designed the ductwork should have been engineered to account for the difference in “load” for various rooms of your home. Load will vary based on the square footage, the number of outside walls and windows, what’s above and below each room, the insulation, and even the number of occupants or appliances in the room. Even a well designed home may have rooms that are too cold or too hot, however. It may be possible to adjust some of the dampers in the ductwork to balance the air, but if that isn’t sufficient ductwork modifications or a zoning system may be required to make each room consistent in temperature.

Noisy/Whistling Ducts

Noisy or whistling ducts are not only annoying but may actually be impacting the efficiency and longevity of your system. The high air velocity that causes noisy or whistling ducts would normally indicate that too much air is being delivered through that particular duct, which is probably causing restricted airflow. This might be a design issue or another problem, but it should be inspected and corrected before larger problems develop.

Dusty/Dirty Ducts

A common concern among homeowners is whether their ductwork is dirty and should be cleaned. It’s definitely possible for ductwork to become dirty and dusty over time. While air is moving through the ductwork, and you’d think that would keep it clean, ductwork isn’t perfectly smooth on the inside. Flexible duct contains spiral wire that creates ridges on the inner surface and metal ductwork is often lined with insulation on the inside. Both can trap dust and other contaminants. While it’s up to the individual homeowner, in many cases the dust that is trapped in your ductwork is harmless and will remain trapped there and will not re-enter your home. Cleaning ductwork is not a perfect process. If you really want clean ductwork, replacing it and starting over is your best option, especially if it is very old (over 20 years).