Factors Determining Duct Noises
Some people find HVAC (heating, ventilation, and air conditioning) noises uncomfortable. Knowing the causes of duct noises can help you silence them. Below are common factors that determine such noises.
Duct design affects air direction and speed within the ductwork. Airspeed and direction determine duct noise levels. For example, ductwork with many twists and turns is noisier than relatively straight ductwork since the former forces air to change direction multiple times.
Other elements of duct design that determine noise levels include:
- Rough inner surfaces that interrupt airflow
- Flexible materials that bend with air movements
- Materials that expand and contract with changes in temperature
Inform your contractor about your noise concerns before installation. That way, the contractor can include design elements that dampen duct noise.
Even properly maintained ductwork gets noisier if it suffers damage or significant wear and tear. For example, duct disconnections or holes make noise when air flows through the openings. Similarly, obstructions within the ductwork can restrict airflow and contribute to duct noise. Lastly, loose duct channels may bang and clang as air flows through them.
Wear and tear, animal actions, and DIY modifications can damage your ductwork. Inspect your ductwork regularly for signs of damage. That way, you can fix or replace damaged sections and enjoy quiet ducts.
Duct dampers control the flow of air within the ductwork. You open dampers to increase airflow and close them to decrease airflow. Controlled airflow determines the air delivery into different rooms, which affects energy, heating, and cooling efficiency.
However, closing too many dampers or fully closing them can restrict airflow and increase air pressure. The increased pressure leads to noisy conditions, for example, by forcing the duct material to expand.
Air Filter Clogging
The air filter traps particles so that the furnace and your indoor environment get clean air. The trapped particles accumulate on the filter with time, so you should regularly clean or replace the filter. The accumulated debris will restrict airflow if you don't clean or replace the filter. Restricted airflow creates noise as the system forces air into the ductwork.
The fan speed determines air volume and pressure within the ductwork. Sending a lot of air at high speed into the duct system increases its noise. An accidental high-speed setting can have such an effect.
In addition, a single-speed air handler that either runs at full speed or doesn't run is noisier than a variable-speed air handler. The single-speed air handler is noisier because it triggers duct expansion every time it starts and duct contraction every time it stops. A variable-speed air handler is quieter since it doesn't start and stop all the time – it just regulates its speed.
Contact an AC service technician for more info.