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Furnace Making a Roaring Noise? 5 Common Causes and Fixes

Troubleshooting a furnace making a roaring noise can be an arduous process. Sometimes the problem isn’t something serious, and you can continue using the furnace as usual. However, if the constant roaring sounds concerning, it’s time to look into the problem.

Your furnace is making a roaring noise because of a faulty blower motor, loose furnace components, problems with the ductwork, and gas supply issues. Go through each of these parts and make the necessary adjustments to stop the roaring.

In this article, I’ll explain what’s causing the roaring noise in your furnace and how to prevent it in the future.

Faulty Electrical Transformer

You’ll often hear a buzzing noise when a strong electrical current passes through electrical cables. The same thing happens with the furnace’s transformer. It matches the furnace’s voltage by lowering the power supply’s voltage levels.

Some furnaces require 24 volts to control minor functions such as timers, ignitions, and temperature control. When you have a failing thermostat, the roaring noise gets louder. 

Contact an HVAC technician to replace the transformer as soon as you notice this problem.

Faulty Blower / Inducer Motor

A blower motor is responsible for blowing hot air throughout your building. You can usually tell that the blower motor is dying because it gives off clear signs. To be more precise, it’s usually the motor’s capacitor.

Here are a few signs that your motor’s capacitor is failing:

  • A faint roaring noise.
  • Furnace not working.
  • Short cycles heating cycles.

Sometimes, a problem with the motor can be fixed with lubrication. Here’s a great video breaking down how to lube the HVAC blower motor:

Loose Furnace Components

The amount of air that goes through a furnace coupled with the motors’ rattling as your house gets heated causes vibrations that shake up the furnace’s housing — resulting in loose nuts and bolts. Loose panels and other parts can cause a roaring noise as they shake violently while the furnace is operating.

An easy fix is to open up the furnace and tighten any loose parts you find. You’ll likely need a screwdriver and a wrench set.

But the best solution is to contact a certified HVAC technician. They know which part goes where and can make your furnace look like new from the inside.

Here’s a great temporary fix while waiting for the technician — use a soft material to cushion loose parts so that they move less.

Problems With Ductwork and Plenum

When you turn on your gas furnace, the gas burners ignite and sustain a flame, which heats the air that circulates through your house. The furnace’s blower directs conditioned air to the plenum and then towards the ducts’ network. The circulated air goes through the return plenum before being distributed back to the furnace.

The ducts and plenum are rather flimsy. If the ducts are too long or the plenum too big, they’ll produce a loud roaring noise.

Here are a couple of ways to fix noisy ductwork:

Adjust the Fan Speed

Your furnace will be noisy when you set the blower fan to a high speed. However, if you reduce the speed of a correctly moving fan, you won’t have enough air circulating through your ducts. So, this is only a temporary fix. Keep reading for a more permanent solution.

Upgrade the Ductwork

Your ductwork has to be large enough to carry the air going through it. Small ductworks increase the HVAC’s static pressure, producing a roaring noise. Increasing the ductwork amount will reduce or outright eliminate the noise.

Your contractor can increase the length of your ductwork near your blower or furnace. If necessary, they can increase your plenum too. When using a single system with multiple zones, your contractor can add bypass ductwork to alleviate the duct’s static pressure.

Because static pressure is a significant contributor to sound problems, increasing or expanding the grills and registers will increase the return air. The HVAC system will supply air more efficiently, eliminating the strange sounds.

Issues With the Gas Supply

A gas valve will typically make a gentle humming sound when working correctly. But when the hum escalates to a disruptive sound, it indicates one of several problems:

  • High gas pressure. This can damage the furnace by overheating. Have your HVAC technician test your gas pressure and adjust it to a normal range.
  • Dirty valve. You need a sediment trap for your gas line. The drip leg is meant to catch any debris before it gets to the gas valve. Water and dirt in the gas valve can cause rusting and corrosion.
  • Incorrectly installed gas valve. A loose gas valve rattles and makes sounds.

Here’s a video explaining how to check the gas valve:

Note that it’s hard to troubleshoot problems with gas supply — one small mistake can cause a mini-explosion. An HVAC specialist is the best person for this job.

Routine Maintenance

Performing routine maintenance checks will prevent all concerning furnace sounds:

  • When winter is coming, look for a professional to ensure that everything runs in good condition.
  • Change air filters regularly to prevent dust and dirt from circulating in your house. The longer an air filter stays on, the more clogged it becomes, and the furnace and blower motor have to work harder.
  • When performing routine checks, ask your technicians to check your ductwork and clean it. You can reseal the dents or use metal duct tape to close off edges and loose joints.
  • Even before you hear noises, your furnace will warn you of a malfunctioning component through the LED warning lights or display. You can identify the error code by referring to the owner’s manual.

Conclusion

Furnaces make all sorts of noises, which is typical for such an elaborate electrical system. When you hear strange noises emanating from your furnace, think back to when you had your routine maintenance check and schedule an appointment. Prevention is key.