Why Your Ducts Are Making a Popping Noise

2017 Feb 03
Posted in: Air Conditioning

Wonder what’s causing that popping noise in your home’s ducts? 

Popping and banging sounds are caused by the movement of duct walls due to pressure changes. Hot air makes your ductwork expand; cold air makes it contract.

How much popping noise you hear depends on 1 or more of these 4 factors:

  1. The shape of your ducts
  2. Your ducts’ gauge rating
  3. The size of your ductwork
  4. Furnace noise

Let’s go into more detail about each of these factors and how you can reduce the popping noise with each.

Factor #1: The shape of your ducts

Duct work comes in 3 shapes: round, square and rectangular.

Round ducts are the quietest; rectangular ducts are the loudest.

This sound difference exists because each shape has a different threshold for the amount of pressure (measured in cubic feet per minute, or CFM) it can handle. Circular ducts can handle the most pressure, followed by square ducts, and lastly, rectangular ducts.

Solution

You could, of course, replace your rectangular ducts with round ones. But that’s expensive.

So an HVAC technician may recommend more affordable solutions like:

  • Wrapping the ducts with fiberglass insulation
  • Inserting duct liners to dampen sound
  • Placing rubber pads to prevent your ducts to rub against surrounding material (like wood)

Contact a heating specialist for recommendations specific to your home.

Factor #2: Gauge rating of your ducts

Metal ducts have gauge ratings, which reflects how strong the metal is. 

The lower the gauge rating, the thicker and stronger the metal. A thick and strong metal can withstand more pressure, therefore making it less likely to expand, which reduces the popping noises. Most home ductwork uses a 24-26 gauge sheet metal, which is a sweet spot.

So, to sum up:

  • Lower gauge rating = stronger/thicker metal = less popping
  • Higher gauge rating (26+) = weaker/thinner metal = more popping

Solution

If everything else in your ductwork and heating system is working perfectly, it could mean you’re ducts have too high a gauge rating (26+). 

The only way to fix this would be to change out the ducts in your system to a stronger, lower gauge duct. This is expensive, so you’ll want to consult a professional to make sure it’s absolutely necessary. 

Factor #3: Size of ducts for your home

If your ductwork is sized too small, you can actually see your ducts expand when you turn on the heat. The increase in pressure makes your ducts expand, which causes the popping sound you’re hearing.

Calculating the right size ductwork for your home is a complicated procedure. This should always be done by a professional. 

Solution

You’ll need a certified air expert to look at your home and perform these calculations for you. If your ductwork needs expanding, your contractor will then provide recommendations on how to expand your system.

Factor #4: Furnace noise

Sometimes popping noises coming from the furnace are carried into the home through the ductwork. 

If you have recently had a new furnace/system installed and the popping noises are new, there is a chance that your ductwork may need some repairs to make it compatible with your new system. These problems are not foreseeable because your old equipment does not have the same indoor blower motor as your new equipment has. Many times the popping issues are not apparent until something is altered or added to the HVAC system. 

The noises may also be caused by a delayed furnace ignition or the rattles and vibrations from the furnace’s fan or blower.

Solution

A heating and cooling professional can inspect your furnace to make sure the ignition is functioning properly. If it is, and the noise is coming from the fan or blower, they can install a flexible duct connector. A flexible duct connector is an air-tight flexible joint, which is inserted between the furnace equipment and the ductwork to reduce noise.

Tired of the popping noise? Call a professional

Contact George Brazil Air Conditioning & Heating to reduce the popping noise in your home. We’ll diagnose the problem and find the solution that works best for your budget and needs.

We’ve been servicing homes since 1955.

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