Even with standard maintenance, HVAC systems can be the sources of occasional mysterious knocking, unbalanced output and other causes for noisy heat. Here are a few common issues, their sources, and and tips to sort them out.
Unbalanced Heating or Cooling
Poor duct design and sealing are often the culprits behind an unbalanced HVAC system. In a perfect world, rooms would be designed with completely balanced temperature distribution. The challenge is a blend of your local climate and construction demands.
Improvements begin by inspecting your ductwork and sealing any leaks. Add insulation to improve comfort for more predictable room-to-room temperatures. Make sure that the air-return portion of a forced-air system is functioning properly because that can also have an adverse impact on room temperatures. One way to ensure this is by undercutting interior doors so that there’s enough space between the door’s bottom and the floor—at least an inch. With that, air can escape to the return vent even when the door is closed.
You can check and adjust airflow by doing a “tissue test” at each room’s supply and return vents. Here’s how: Switch your thermostat to “fan” and then go from duct to duct, holding a tissue in front of the vent to determine airflow. Supply vents should blow the tissue toward you with a good little gust, and return vents should pull the tissue right up against themselves.
Oil-Canning of Ducts
This noisy heat phenomenon happens when metal ducts rapidly fill with air as your system starts up, expanding with a big bang, just like an old oil can. Hence the name. Repair is easy, a simple matter of proper reinforcement of the ducts. Just to be sure that oversized airflow or other elements aren’t the issues, it’s wise to have an HVAC technician check things out and help determine safe solutions that’ll keep the air moving, but much more quietly.
Banging pipes and radiators are common noisy heat complaints when it comes to steam systems. The knocking sound is the result of tiny steam explosions that occur when water collects in the radiator rather than heading back toward the boiler to be reheated
If a little knocking sets your world rocking, there’s an easy fix. Literally, tip the balance by repitching the unit so it sends the excess water back toward the unit’s inlet valve. You can do this by adding a shim—a small piece of wood—under the legs on the end of the radiator opposite the inlet valve.
Cold radiators are another cause of noisy heat. If too much air gets trapped in a hot water radiator, water won’t be able to move smoothly through it, and you’ll wind up with the radiator either totally or partially cold when the heat is on. Occasional “bleeding” of the radiator will help you maintain efficiency. To do this, you’ll need a radiator key, a simple wrench designed in the shape of a key to fit the air bleed valve on the top of the radiator.
Turn the heat on and once all the radiators are warm, use the key to drain out any air that has become trapped at the top of the radiator. Once hot water starts to “spit” out of the bleed valve, you can shut it off and you’ll find that that the entire radiator will heat. Be careful though, since the hot water can burn you if you’re not cautious.