A low rumble is a normal sound when your gas or oil-fired furnace kicks on. However, if that rumble is louder than usual—or lasts longer than usual—this could indicate a very serious problem with your burner.
The most common cause of rumbling furnace noises is a buildup of soot and grime on the burners. A tremendous amount of gas goes through your furnace during the heating season, and if you don't have the system professionally cleaned and adjusted each year, grime can start building up.
Loud Bangs, Rumbles, Knocks, or Booms
Loud noises like this are a sign of a build of gas in a furnace. The noise you hear can mean your heat exchanger is at risk of cracking. Even worse, it's a sign that something dangerous could happen if you continue to use your heater.
Thumps and bumping noises, like an unbalanced washing machine, often indicate an unbalanced blower wheel or motor. This is a serious issue that requires immediate HVAC repair. The blower wheel and motor are major furnace parts and you don't want them bouncing around.
Once a heating cycle begins and air resumes circulation through the ducts, you may notice a vibration when the furnace starts – this is the noise produced as the metal components vibrate against each other. Disconnected ducts aren't typical but can result from poor installation.
A common reason for furnace buzzing is a loose transformer box. A furnace transformer regulates the incoming voltage to an appropriate voltage for the furnace to use. This is more common after a new installation. With an older furnace, the transformer may be malfunctioning and needs to be replaced.
Several factors can contribute to a flickering or wavering furnace flame: Airflow Issues: One common cause of flame flickering is turbulent airflow within the furnace. This can be due to a dirty air filter restricting the flow of air, blocked vents, or even the incorrect installation of ductwork.
First, know if you have a gas, electric or oil furnace. Electric furnace installation tends to be the least expensive, ranging between $3,000 and $7,000, according to HomeAdvisor. Installing a natural gas furnace falls in the range of $3,800 to $10,000, and an oil furnace ranges $6,750 to $10,0000.
Usually, it's because the bearings of the motor need to be lubricated or replaced entirely. If this is happening, you'll notice how much louder and more howl-like noises get over time until finally, they begin howling through your home. Fixing howling noises caused by a noisy blower fan is pretty simple.
Rattling (Inside the House), Clanking or Banging
Like “thwapping,” these sounds could be related to the furnace's blower assembly or motor, and are likely due to something being either loose or broken. If you hear louder banging sounds when the blower is running, shut the system off until you can get help.
If your furnace is making an obnoxious noise, it's likely because the furnace blower motor is turning on and off as part of normal heating furnace cycles. Make sure your thermostat is set properly to the desired temperature and off when you don't need heat (like overnight).
A failing blower motor may emit unusual sounds. This may sound like screeching or squealing if it has bad bearings. You may hear a rattle or a banging sound if something inside the motor has broken or come loose.
While costs can vary, homeowners can typically expect the following range: Standard Blower Motors: These might cost between $400-700, excluding labor. Advanced Multi-Speed or Variable-Speed Motors: These are generally more expensive, with costs ranging between $650-1250, not including labor.
Rumbling can usually be caused by an issue with the blower wheel in your heater. Other causes could be connected to a faulty burner or a rapid expansion and contraction of your air ducts.
Any furnace that burns fuel produces carbon monoxide as a byproduct. This is the same for any appliance in your home that burns fuel, such as a gas range. Therefore, if your furnace uses natural gas, propane, or oil to make heat, your furnace creates carbon monoxide. Electric furnaces do not create carbon monoxide.
Gurgling Noises
In newer, high-efficiency systems, exhaust fumes are vented from the unit but can produce condensation from moisture in the air. If your furnace struggles to drain this condensation properly, it can cause gurgling, dripping, or bubbling sounds.
It is usual for your furnace to make low sounds while it's operational. However, if you hear very loud, unusual noises coming from your furnace, something could be wrong. Typically, when you start your furnace, it produces some noises when the heating cycle starts.
For 1- to 2-inch filters, replace them every 1 to 3 months. For 3- to 4-inch filters, replace them every 6 to 9 months. For 5- to 6-inch filters, replace them every 9 to 12 months.
The Average Furnace Lifespan
A well-maintained furnace can last at least 15 to 20 years, but completing annual maintenance and being diligent with repairs can extend its life even longer.
Your base homeowners policy will cover many types of damage to your furnace. An extra endorsement known as Equipment Breakdown Coverage (EBC) will give you additional coverage for certain types of mechanical or electrical failure.
Identifying the Priciest Component: The Heat Exchanger
Due to its complex role, a failure or crack in the heat exchanger can lead to serious issues, including dangerous carbon monoxide leaks. This makes furnace repair essential to maintain safety and functionality.
If it's revving up excessively it could be a sign of an overactive blower motor. This may result from issues such as a malfunctioning thermostat, incorrect fan settings, or a clogged air filter. A simple adjustment or maintenance can often rectify this and restore the balance to your furnace's performance.
Blower Wheel Issues
If the blower wheel is unbalanced or has become dirty, it can cause the furnace to vibrate when starting. Regular furnace maintenance, including cleaning, can prevent this from happening. If the blower wheel is damaged, it may need to be replaced to stop the vibrations.
While all furnaces generate some ambient noise, they run quiet enough not to be disruptive most of the time. However, loud buzzing or humming can indicate various mechanical or electrical problems, either when the furnace starts up or throughout its operation.