How Do I Know if My Blower Motor is Bad on a Furnace?
A furnace blower comprises of a motor and fan blades. Its function is to pull air from the house via the return air ducts and later force it back to the house after heating/cooling it via the supply air ducts.
The furnace blower motor is located at bottom of the furnace, next to the air filter slot. When the blower pulls air from the house, it forces it through the filter to remove dust, pollen, dander, lint and other impurities.
Due to the fact that a furnace motor is always in motion, wear and tear is inevitable. At some time you will need to replace it.
So, how can tell you if your furnace blower motor is bad and that it needs to be replaced? Or rather, when should a furnace motor be replaced?
The following are the signs that a furnace blower motor is bad:
- Weak airflow
- No airflow at all
- Unusual/strange noises
- High energy bills
- Overheating (burning smell)
The average lifespan of a blower motor just like the furnace is 15 to 20 years. Properly sized and maintained blower motors will lost for a long time while undersized and poorly maintained motors will only last a few years.
Note: The overall maintenance of your HVAC system also affects the lifespan of your blower motor. For instance, failing to change the furnace filter will overwork the motor resulting in a reduced lifespan.
A bad furnace motor will make screeching, squealing, rattling, knocking or banging sounds. Screeching/squealing sounds are a sign of a bearing problem while rattling, knocking or banging noises are a sign of a broken/damaged part.
It costs between $250 and $900 to replace a furnace blower motor depending on size, brand, and area among other factors. However, it can cost as much as $2000 for high-end or large motors, or if the job takes longer than expected. If you still have a warranty, you only need about $150 for labor.
How a Furnace Blower Motor Works
A furnace is located somewhere in the basement, crawlspace, attic or even a utility closet. It is connected to both the return and supply air ducts.
The return air ducts carry air from the house to the furnace while supply air ducts carry heated/cooled air from the furnace to the house. Inside the house there are supply and return air vents where air from the house is delivered or sucked in respectively.
As I mentioned, the blower motor is connected to a fan (to form what we call a blower) and are located at the bottom of the furnace if you have a vertical furnace. With a horizontal furnace, the blower will be located on the side of the furnace, where the return air comes in.
The furnace filter is always located on the return air side of the furnace. That is because its function is to clean the air from the house (and also ventilation air) before it reaches the combustion chamber.
When the thermostat calls for heating or cooling, the furnace blower is powered up and it starts to rotate. The rotating fan pulls in the air already inside the return air ducts, which creates a pressure differential.
That causes the air in the house to be sucked inside the return air duct, past the air filter and into the furnace. If that is during winter, the air passes through a heat exchanger where it absorbs heat from it.
During summer, the air is moved across an evaporator coil where a refrigerant absorbs heat from the air and cools it in the process.
After heating or cooling, the blower forces the air out of the furnace through the supply air ducts. The air is delivered in the house through the supply air vents.
That cycles goes on and on until the house is sufficiently cooled or heated. The thermostat will then send a signal to the furnace and the blower motor will stop automatically.
Note: It is very important to regularly change your furnace filter. Ideally, a furnace filter should be changed after every 90 days. Change it monthly if you have many pets and/or suffer from allergies or asthma.
Failure to change the filter will cause it to clog and thereby restrict the flow of air to the furnace. That will force the furnace blower motor to work extra hard which will result in overheating and premature failure.
Types of Furnace Blower Motors
There are 3 types of furnace blower motor in terms of their speeds. These are:
- Single-speed blower motors
- Multi-speed blower motors
- Variable-speed blower motors
Single-speed motors as their name implies have a single-speed. They are either running at 100% of their speed or they are off. As a result, these motors tend to be very energy-inefficient.
Multi-speed blower motors on the other hand can run at 100% of reduced speeds. They kick in at 100% of their speed and later slow down just to maintain the temperature of the house and hence they consume less energy.
Variable-speed blower motors are the latest technology of motors and are therefore the most energy-efficient. The blower motor speed can be varied (adjusted) relative to the indoor temperature which means the motor will in most of the time be running at low speeds.
Apart from blower motor speed, there are also 2 categories of furnace blower motors:
- Direct drive motors
- Belt drive motors
Belt drive motors are found in old furnaces. Here, the motor shaft is connected to a pulley and a drive belt is used to connect it to the fan.
Direct drive motors are the ones found in most modern furnaces. With these motors, the fan is connected directly to the motor shaft
Signs of a Bad Furnace Blower Motor
The following are the signs that your furnace blower is bad and that it needs to be replaced. Please note that in some of these instances the problem may not even be a bad motor but something associated with it that can be fixed by an HVAC technician.
1. Weak or No Airflow at All
The first sign of a bad motor is when there a significant reduction in the airflow from the vents. The problem is often caused by a clogged blower due to accumulation of dust and debris.
In other instances, a weak airflow from the supply vents can be caused be leaking ducts. It is estimated that more than 20% of air in most homes with central HVAC systems is lost to leaks in the ductwork.
Of course if leaky ducts are the problem you do not need to replace the furnace blower motor. However, if the reduction in airflow is caused by an aged motor, you will have no alternative other than to replace it.
In instances when there is absolutely no airflow coming from your vents, the blower motor could be completely dead and without a doubt you will need to replace it. The problem can however be caused by other issues like a bad relay, thermostat or fan control but it would take an HVAC technician to figure it out.
2. Higher than Usual Energy Bills
If your furnace blower motor is nearing its last days, it will need to work harder to keep the whole house properly heated/cooled. The harder it works the more energy it will consume.
If you have therefore noticed a sudden increase in your energy bills, it could very well be as a result of an aging furnace blower motor that needs a replacement. This is especially the case when the furnace is about 15 to 20 years old.
I should however say that a sudden increase in energy bill can be caused by other problematic appliances and not just the furnace blower motor. For instance, a faulty electric water heater can also cause the power bills to shoot through the roof.
Overheating in a blower furnace motor can be caused by dirt or age. If dust and other particles accumulate around the blower motor, they will create friction resulting in the overheating of the motor as it rotates.
That problem can be solved by an HVAC technician so in this case you do not need to replace the motor.
As I have mentioned above, an old furnace blower motor will need to work extra hard to keep up with the temperature regulation demands of your house. The harder a motor works the more it is likely to overheat, causing wear and tear.
But how can you tell that your furnace blower motor is overheating? A good sign of an overheating furnace blower motor is a burning smell coming from the vents.
Since a furnace is equipped with a limit switch, you will notice that after overheating the entire HVAC system will turn off. The limit switch is the blower motor’s failsafe, preventing it from further damage.
4. Unusual Noises When You Turn on the Heat
A furnace is not a quiet appliance (even those with the quiet variable speed motor). There is that distinct noise which a furnace is supposed to make as it runs.
If however you hear a screeching, squealing, rattling, knocking or banging noise from your furnace, all is not well. You may need to fix or even replace the furnace blower motor.
A screeching or squealing sound from the furnace is a sign that there is problem with the motor’s bearing or belt. Something as simple as lubrication can be enough to fix the problem.
On the other hand, if you hear rattling, knocking or banging noises, it is a sign that a component of the furnace blower is broken or outright damaged. In that case you will need to repair or even replace the blower motor.
When you hear unusual sounds from your furnace, I would advise that you shut it down and contact an HVAC technician immediately.
Should You Replace a Furnace Blower Motor or Buy a New Furnace?
When faced with a problematic furnace blower motor, it is not unusual to wonder whether to replace just the blower motor or simply buy a new furnace. What are the pros and cons of each?
The first thing you should do is perform a cost-benefit analysis of each. In all these, cost is always a major factor.
As I mentioned, it costs $500 on average to replace a furnace blower motor. On the other hand, it costs between $2000 and $8000 to replace a furnace depending on model, energy efficiency and size of house among other factors.
As you can see, replacing just the blower motor is cheaper. But when should you opt to replace the whole furnace?
I would say that if your furnace is not more than 12 years old and you have religiously maintained it, it is has some life still left in it. In that case, it makes sense to keep the furnace and only replace the blower motor.
On the other hand, if your furnace is 15 years or older, its best days are well behind it. Instead of just replacing the blower motor and leave the furnace (which will need replacement soon anyway) I would suggest buying a new furnace.
When your furnace is less than 5 years old and is already being problematic, it could be a manufacturer defect. The good thing is that it will still be under warranty and you can have it replaced for free.
Also, if you don’t intend on selling your house, sometimes it makes sense to just buy a new and more efficient furnace. That way you will be sure that you will not need to invest in a furnace for the next 15-20 years, as long as you regularly service it.
And basically those are the signs that your furnace blower motor is bad and needs to be replaced. However, you will most likely need an HVAC technician to advise you if you need a replacement or a repair.