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Furnace Not Blowing Air Through Vents? 7 Common Causes

Your furnace not blowing hot air through the vents is a complex problem that many parts of the HVAC system can cause. Without proper ventilation and ductwork, your furnace has no way to distribute hot air throughout your home during winter. So, what do you do when you start your furnace and discover no air is coming out of the vents?

Your furnace isn’t blowing air through vents because of problems with the ductwork, air filter, blower motor, or the furnace itself. You can fix the problem by cleaning your ductwork and vents, fixing air leaks, replacing the furnace filter, and ensuring your furnace receives gas and electricity.

In this post, I’ll discuss the most common reasons why a furnace isn’t blowing hot air through the vents and what you can do to solve this problem.

Blocked Air Vents

A blocked air vent won’t allow any airflow. Check that you don’t have any objects placed in front of the supply vents. Even something as light as a curtain can block plenty of air.

While at it, check to see if the vents are open. Never leave your registers closed, even if you don’t intend to warm a specific room. Closed vents force the blower motor to work harder to direct the heated air to other rooms, which can skyrocket your electricity bills and put your furnace at risk of premature breakdown. 

But how well your vents blow air into your room will also depend on the amount of air going back into the system. If the return vents aren’t pulling in enough air, even the air that comes out will be too little to make any difference. It’ll feel as if the furnace isn’t blowing any air, but there simply isn’t enough hot air to warm the room in the real sense. 

As with the supply vents, make sure nothing stops the return vents. That way, there will be sufficient air going back into the system, which means there will also be enough for your living spaces. 

Leaky Ductwork

If you’ve checked your vents but still can’t feel air blowing out from the furnace or some rooms feel warmer than others, the problem may be your duct system. It could be that air is escaping before it reaches your supply vents. 

Most of the leaks will be from the joined sections of the ventilation system. If the joints weren’t appropriately tightened during installation, they could let the air out to warm unintended areas. 

The only way to solve this problem is to seal the leaks. Locate the joined sections of your duct system and apply sealant around them; you’ll notice an immediate improvement to airflow. 

If this doesn’t help, your problem may have resulted from a disconnected air duct. Remove your heat registers and examine the ventilation line with a mirror or flashlight. If the separate piece is within a reachable area, refasten the duct with screws and apply a sealant to the joint. 

However, there are times when you can’t identify the air leak. Unless you have a fog machine at home, you’ll need to work with an HVAC expert. They can inspect the ductwork with a special camera to locate the disconnection and suggest ways to access it for repair. 

But leaky and disconnected ducts aren’t the only reasons airflow may be restricted to the vents. Sometimes the duct system is just clogged with dirt, making it difficult for air to move smoothly through it. 

A blockage in the ductwork usually occurs due to a clogged air filter. If you haven’t replaced your furnace filter for some time, the trapped filth could make its way into the ventilation lines, building up clogs that hinder airflow. 

Unless you know exactly where the blockage is, clearing clogged ducts is a job best left to a professional, as it requires scoping the entire ventilation line to identify the obstruction. 

Dirty Air Filter

A clogged filter is a common cause of a furnace not blowing hot air through the vents. The trapped dust and debris limit airflow entering the heat registers, resulting in insufficient air leaving the system. 

Also, since the blower fan won’t have enough air to blow through the vents, it’ll have to run longer to supply the sufficient air needed to keep your home warm. This strain will cause the heat exchangers to overheat, putting the furnace in danger. However, the unit will shut down automatically to prevent damage. 

If you can’t feel any air coming from the vents, your furnace may be just shut off. Start your troubleshooting process by turning the furnace on. Remove the dirty air filter and replace it with a new one. 

To keep the unit working efficiently, make sure to change the filter every 30 to 90 days. If you have pets, smokers, or people with respiratory allergies in the house or live in a highly polluted place,  replace your furnace filter more frequently. 

Tripped Circuit Breaker

The furnace still isn’t blowing air through the vents? 

Check whether it’s even getting power. If there was a recent power outage, the circuit breaker might have tripped, preventing the furnace from turning on. 

Open the electrical box and locate the furnace switch. If it’s turned off, flip it back on. Then turn the furnace on and see if it powers on. 

If there still isn’t any hot air, go back to the breaker panel and see if the switch is on. Sometimes the circuit breaker switch drops immediately because of a malfunctioning component. It shuts the furnace down as a safety measure to stop it from overheating or even exploding.

Don’t turn the switch on if it keeps tripping. Instead, have it checked by an electrician. An expert can determine if a defective component causes the tripping or the circuit breaker is just faulty.

Thermostat Problems

The thermostat manages the heating cycle in your furnace to allow hot air to blow through the vents. Perhaps your thermostat isn’t communicating with the furnace, which is why you’re not getting any air from the vents. 

Thermostats, especially the programmable kind, are rather complex pieces of tech. The more features the device has, the more likely it is something goes wrong. Here are a few things you can do to make sure the thermostat can communicate with your furnace:

  • Ensure the thermostat is set to HEAT, not COOL or OFF.
  • Raise the thermostat temperature a few degrees higher than the room temperature and wait to see if hot air comes out of the vents. 
  • Ensure the device is set to the correct day and time.
  • Inspect the thermostat wiring for loose or broken cables. 
  • Check the batteries. If your thermostat isn’t working because of dead batteries, it’ll reset to the default settings and won’t turn the furnace on. 
  • Open the back cover of the device and blow out any dust. Dirt buildup on sensors and other internal components of the thermostat can cause the device to send false signals to the furnace, resulting in the unit not coming on and blowing air through the vents.
  • Consider the location of the thermostat. If your ventilation produces air then suddenly stops, your thermostat placement could be the problem. If it’s positioned near a heat register, the heat from the vent will cause the thermostat to record a higher temperature than your room demands, which will shut down the furnace prematurely. 

Defective Blower Motor

The blower motor blows the hot air produced by your furnace into your home. It carries out this task by rotating a fan that pushes the air into the duct system and finally to the vents to circulate throughout your home. 

If the blower motor is faulty, it’ll have trouble pushing air through the ductwork, resulting in insufficient airflow. Several things can make your blower motor malfunction, including dust and dirt buildup, a faulty capacitor, or an aging motor. Have an expert clean and replace failing parts for you. 

If no hot air is coming from the vents altogether, there’s a good chance the blower motor is dead and requires a complete replacement.

Usually, when a blower motor starts to misbehave, the furnace shuts down to prevent severe overheating. If your furnace isn’t blowing air through the vents, it could be that either the blower isn’t delivering enough air or the unit has shut off. Either way, you’ll need to call in an expert to diagnose and fix the problem. 

Closed Gas Valve

If you’re using a gas-fueled furnace and the unit isn’t blowing air through the vents, check if the gas valve is turned on. Even if you try all the fixes we’ve discussed above, if your furnace isn’t getting any fuel, it has no way to heat your home.

Locate the gas valve and check the handle’s position. If it’s perpendicular to the gas outlet, it’s closed. Turn the handle to lie parallel to the gas line. This will open the gas valve and, hopefully, fix the problem.

How To Improve Furnace Airflow

Now that you know the most common causes of a furnace not blowing air, let’s look at a few things you can do to keep your unit in good shape so that you don’t have to deal with airflow problems anymore.

Schedule Preventative Maintenance

As the saying goes, “Prevention is better than cure.” So, make a point of giving your furnace the tender loving care it deserves regularly, and you’ll never have to worry about it again.

The good news is that you can leave this job to a professional.

A licensed HVAC technician will tune up your heating system as needed to keep it functioning optimally. They’ll inspect the unit, test it, and address any issues that restrict airflow, like dirty filters and improperly sealed ducts. 

Have Your Ducts Cleaned Professionally

While your furnace filter traps dirt, dust, debris, and other pollutants, keeping them from entering the unit, some of it can eventually make its way to the duct system if it’s left to accumulate for too long. 

Over time, dirt can build up inside the ductwork, restricting airflow into the vents. Luckily, there’s nothing professional duct cleaning can’t fix. Talk to your HVAC guy about it and see if you can schedule it as a part of your furnace maintenance program. 

Get an HVAC Ventilator

If you don’t mind spending a little more on your heating system, invest in a ventilator. An HVAC ventilator pushes out stale, stagnant air and pulls in fresh air, maintaining sufficient airflow in and out of the heating system. 

But these devices do more than improve airflow; they also expel moisture from the air, keeping your living area more comfortable. And not just that — they also trap energy from the hot air coming out of the supply vents and pre-heat the air going back into the system. This puts less stress on the furnace, boosting its overall efficiency and expanding its lifespan. 

Conclusion

When a furnace isn’t blowing air through the vents, it can be a frustrating problem to deal with. If you’re experiencing this problem, ensure the vents are open, the ductwork isn’t leaking air, the blower motor isn’t malfunctioning, and you have a clean filter. 

You want to make sure the unit’s turning on, too, so check that you don’t have a tripped circuit breaker, the thermostat is working correctly, and the unit’s getting fuel.