Banging, rattling and popping air ducts are annoying – even a little unnerving when they creak in the night! Are your HVAC ducts making a lot of noise? This guide will help you figure out why they are so noisy and what you can do about it.
Diagnosing the Problem: Why are the Ducts So Loud?
There are several reasons why the HVAC ducts in your home may be making noises. Most homes have sheet metal ductwork which tends to be the noisiest material for ducts. Below is a list of noises your ducts may be making and the most likely cause for each noise.
Are duct sounds normal? We answer that too.
1. Rattling – If you are hearing rattling noises coming from your HVAC ducts it is probably because some part of the ductwork has come loose, causing the disconnected pieces to rattle when air is moving through the ducts.
2. Clanging – Banging sounds are often caused by loose vent dampers that are blowing open and shut as air flows through them.
3. Popping, Ticking, and Banging – These are the most common ductwork noises. They are caused by the movement of duct walls due to pressure and temperature changes. Hot air makes ducts expand while cold air makes them contract, so every time you turn on the furnace or air conditioning, your ductwork is going to be prone to movement that causes noise throughout the house. The more static pressure in your ductwork, the louder it will be.
Solving the Problem: How to Quiet Down Noisy Ducts
Fortunately, there are lots of ways to make your ducts quit banging, clanging, and rattling. Here is a list of options to consider when trying to make your duct work quieter:
Vent Damper Upgrade
If the main sound your ducts make is clanging or banging, you likely have vent dampers that are blowing open and slamming shut. The easiest way to fix this is by replacing your old vent dampers with spring-loaded backdraft dampers. As the name suggests, this kind of damper is designed to pop open only when it is supposed to and will remain closed the rest of the time. Spring-loaded backdraft dampers can be purchased online for $20 – $30 and require a simple installation. Goodbye clanging!
Change the Filter
The airflow in your ductwork could be seriously restricted by dirty ducts or a clogged air filter. Changing a dirty filter regularly and cleaning the ducts as needed (if needed) will work wonders for your HVAC system. Not only will it improve the overall efficiency of your heating and air conditioning, but it will also help to keep your system running quietly.
Consistent Maintenance
Having consistent maintenance done on your ductwork will help reduce noise caused by loose, dirty, or faulty ducts. Experts recommend getting an HVAC maintenance checkup by a professional every fall for the furnace and every spring for the air conditioner. However, if your system is running well and not making noises, one annual checkup to cover all the equipment and ductwork is sufficient.
Static Pressure Issues
The number one cause of noisy ducts is static pressure that is too high. And this is a tough problem to solve. When the HVAC system attempts to move more air through the ducts than your ductwork can accommodate, the ducts will expand, causing popping and banging sounds. Once they are turned off again or the pressure is decreased, the duct walls will contract back to their original size, causing even more noise. Here is a list of common factors that affect the static pressure in your ducts:
1. Duct Shape – The shape of your ducts has a big impact on how much static pressure the duct walls can handle. Round ducts can handle the most static pressure. Square ducts aren’t as good, but they are quieter in this regard than non-square rectangular ducts, which tend to be the noisiest.
2. Gauge Rating – Metal thickness is called “gauge.” The way to read the gauge rating is a little counter-intuitive! The higher the gauge rating of the metal, the thinner it is. A low gauge rating means the metal is thicker. The thicker the duct metal is, the more static pressure it can handle, and the less noise it makes. An average home’s ductwork has a 24–26 gauge rating. The only way to lower the gauge rating is to replace your ducts with thicker ones, which is an expensive project. Make sure to have an HVAC professional inspect your ductwork beforehand to see if this is the right step for you.
3. Single Return Duct – If there is only one return duct for the entire HVAC system, the static pressure is likely to get too high for the return duct to handle, creating excess noise. A single return duct is common in small homes and condos and can only be fixed by installing more ductwork to reduce the static pressure.
4. Duct Size – Your ducts could be too small for your house! Ducts that are small in diameter can’t handle much static pressure, so if the pressure builds up beyond their capacity it may cause loud banging and popping noises. For smaller homes, small duct size usually isn’t an issue, but larger homes may need to expand the size of their ducts in order to reduce noise.
Duct Silencer
One option to consider to reduce duct noise in round ducts is a duct silencer, also called a duct muffler. Indeed, they look like a muffler with double-walled design and insulation that reduces vibration and other sources of noise. Air duct silencers are installed near the noisiest parts of the HVAC system, such as the air handling unit or fan. These mufflers are 24” to 36” in length. A section of the ductwork is removed and replaced with the silencer. You’ll find that adding a few silencers will lower noise but not eliminate it.
Variable Speed Blower
Many homes are equipped with a single-speed blower for the air conditioning and heating system. To control the air temperature in the house a single-speed blower will turn on or off as needed. However, each time the air conditioner turns on and off it makes noise as the ductwork expands and contracts.
A great solution to this is to upgrade to a variable-speed blower that adjusts the air speed. It runs at higher speeds when your home needs a significant temperature change. But it slows down to maintain the temperature and prevent over-heating or cooling. A variable-speed blower doesn’t turn on and off frequently like a single-speed blower, and it runs at a lower speed much of the time. As a result, it is much quieter. It is also the most energy-efficient blower option because it does not use unnecessary energy.
Insulate
A great option for ductwork noise reduction is to have a professional technician insulate and line your ducts. Or do it yourself. This will muffle sharp banging and popping noises and improve the energy efficiency of your home. Win-win!
Go Ductless
If you have a particularly noisy HVAC system that needs constant attention and expensive upkeep, consider a mini split system. Ductless mini splits make very little noise when turning on and off. Most are more energy efficient than standard split systems. A multi-zone ductless system allows you to set different temperatures for each zone – less heat in unused spots, for example, while keeping the living room and kitchen, where people gather, warmer. Or a ductless system can be turned off in an unused guest bedroom while it works in the rest of the house. This allows homeowners to save money on their heating and cooling while providing a quiet alternative to the ducted HVAC system.
FAQs
Does noisy ductwork mean something is wrong?
Not necessarily! An HVAC system that is functioning properly will naturally make some noise. But if it is rattling or whistling, there could be gaps, disconnected spots or leaks. If you are concerned that there may be something wrong with your ductwork, schedule a maintenance checkup with an HVAC technician. They should be able to find ways to make the noise quit.
How can I tell if my ducts need to be cleaned?
Do they smell bad? Have they been infested by rodents? Here’s our opinion: Ductwork cleaning can be a scam. It’s a way for HVAC companies to make extra money – and duct cleaning “specialists” to justify their existence. However, if you’re smelling molding odors coming from the ductwork, or if you know there have been a lot of mice in them, you might need them cleaned. But first, have a qualified HVAC technician identify the cause of the smell and solve the problem first. Then have the ducts cleaned by the HVAC company. Here is more pro-quality info on this debatable topic – Signs Ductwork Needs Cleaning.
Is installing a duct muffler or silencer a DIY project?
Sure. If you’re handy and have metal snips and other hand tools, you can do it yourself. In fact, you can save money making your own duct silencer, as this video shows.
Can I DIY ductwork insulation?
Sure. In fact, we have a page on insulating ductwork – with steps – that you might find useful.
Should I repair or replace old ductwork that is noisy?
Consider repairs first, since it is much more affordable. We address this topic on this page called Insulate Old Ductwork or Replace it?
I think the noise in my ducts is caused by airgaps and other leaks. What’s the solution?
Inspect exposed ductwork, locate leaks and seal them. And then consider insulation to prevent or limit leaks. It will also make them quieter. See the Pick HVAC guide for 3 methods of effective duct sealing.
