One of the components on a furnace that can go bad is the furnace inducer. A failed or failing inducer can prevent the furnace from starting. It can cause the furnace to shut down during a heating cycle. For some furnace designs, the failure of a supporting part may cause the inducer to not operate correctly. And replacing this supporting part may allow the furnace inducer to operate normally. We can usually identify when an inducer is weakening during our annual furnace clean & check. It can then be replaced before the really cold weather hits.
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Combustion Blower Designs
A furnace inducer is a type of motor driven combustion blower fan. The function of the inducer is to bring fresh air into the furnace combustion chamber. The inducer also expels products of combustion through the furnace heat exchanger and out the furnace flue.
Webster defines induce as to lead or move by persuasion or influence. Combustion blowers come in two general varieties, forced draft blowers and induced draft blowers. Many older industrial scale boilers have both a forced draft combustion blower and an induced draft combustion blower. The blower establishes the correct air flow through the unit.
Forced Draft Blower
In residential furnaces, the induced draft blower is used instead of the forced draft blower. What is the difference? A forced draft blower would be located on the inlet side of the furnace heat exchanger. Any leak that might develop in the furnace heat exchanger would result in combustion gasses passing through the leak into the room. This would not be good for the safety of the home occupants as products of combustion can be poisonous.
Induced Draft Blower
Induced draft blowers are located after the furnace heat exchanger. Any leak in the furnace heat exchanger would result in room air being pulled into the heat exchanger. For this safety reason, residential furnaces that have combustion blowers use an induced draft blower. The products of combustion are pulled (induced) from the heat exchanger and are directed out the furnace flue to the outside.
Furnace inducers for Higher Efficiency Furnace Designs
Modern furnaces are equipped with furnace inducers to improve the efficiency of the furnace. Ultra high efficiency furnaces have an additional secondary heat exchanger. The furnace inducer is needed to move the products of combustion across the primary and secondary heat exchangers. The furnace inducer allows furnaces to attain a higher AFUE rating.
WARNING: Accessing components behind the furnace panels involve high voltage equipment that poses serious electrical shock risk. Follow all safe electrical work practices and ensure that only qualified, trained service technicians perform repair activities. Hazardous Voltage! Failure to disconnect power before servicing could result in death or serious injury. Disconnect all electric power, including remote disconnects, before servicing. Follow proper lockout/tagout procedures to ensure the power cannot be inadvertently energized.
A typical residential furnace has an upper panel and a lower panel. The furnace inducer is usually located behind the upper furnace panel. It is often located in about the center position behind the upper furnace panel. In the photo below of a high efficiency Trane furnace, the furnace inducer is identified. Tips on troubleshooting a gas valve failure are available here.
No Furnace Inducer on Very Old Furnaces
Very old residential furnaces did not usually have inducers. The photo below is of an older Lennox furnace that was not designed to use an inducer.
As you can see in the above photo, there is no combustion blower present. The products of combustion passed through the heat exchanger and then up out the furnace flue by natural convection. The hot furnace combustion products are less dense than surrounding air. The difference in density is what drove the flow of the furnace gasses out the flue. There were limits to the efficiency of these older designs. Even the newer 80% furnaces of today have inducers that improve the efficiency of the furnace.
Some Older Furnace Inducer Designs
The photo below shows an older Carrier 80% furnace. The inducer is in the center of the photo. There is a little fan covered by a metal cage that cools the inducer motor. This inducer makes use of a shaded pole motor. The parts of this older style furnace inducer are constructed of metal as the flue gas passing through the inducer is very hot.
The photo below is of an inducer from an older ICP furnace. This inducer is also made of metal as the flue gasses leaving the heat exchanger are hot in this furnace design as well. Hot flue gasses mean the furnace is not as efficient as is possible with modern technology. The motor driving this inducer is the black cylinder looking component with the copper windings visible inside the motor.
The photo below is of a furnace inducer we replaced in a 95% efficiency furnace. The inducer had failed preventing the furnace from running. This particular inducer is manufactured by FASCO. FASCO makes many blower and motor designs. According to the FASCO website, they lead the industry in direct replacement inducers and are installed in a number of furnace designs. These include Trane, Nordyne, Lennox, Goodman, ICP, York, Rheem, and many more
Plastic Designs vs Metal Designs
As is evident from the above photo, the inducer fan housing is made of plastic in this model. It can be made of plastic because this high efficiency furnace operates at a lower temperature. The hot combustion products pass out of the primary heat exchanger and pass into a secondary heat exchanger. The secondary heat exchanger removes additional heat from the combustion gasses. The temperature of the gasses leaving the secondary heat exchanger are low enough to enable plastic inducer fan components.
The photo below shows the large plastic inducer fan housing. And the actual inducer fan wheel can be seen through the central hole in the housing. This inducer fan itself is also made of plastic.
The inducer motor drives the inducer fan wheel. The products of combustion are pulled from the outlet of the secondary heat exchanger, through the inducer fan wheel, and then out the furnace flue. In these high efficiency furnace designs, PVC piping can be used as the furnace flue.
Check out the video below for a little more information about furnace inducers.
Preventing Furnace Inducer Failure
When a furnace inducer fails, it is a fairly costly repair. The furnace will not operate with a failed inducer and this often happens on one of the colder days of the season. Even if the inducer is beginning to weaken but is still running, the furnace may not operate. Pressure switches may keep the furnace from running. If is for safety reasons that the furnace automatically shuts down on a failing or failed inducer. The furnace could overheat if an inducer is failing. And an overheating furnace causes some other problems and shortens the life of the furnace.
Fortunately, we can usually identify when an inducer is beginning to weaken when we are doing a pre-season furnace clean & check. Many of our Omaha customers have us out in the fall to perform this important furnace service. This pre-season service helps to keep your furnace operating trouble free all season long. It gives us a chance to identify parts when they are weakening and get them replaced before they fail. For a list of HVAC maintenance items that homeowners can perform to help ensure their systems operate well, refer to this blog.
This is even important for furnaces that are still under warranty. Many times a manufacturer will insist that warrantied parts be provided directly from the factory. Calling us out for a clean & check when the weather is still mild allows us to replace the part before the really cold weather hits. And it gives great piece of mind knowing that your furnace is well maintained and you can rely on it.
Accurate Heating & Cooling has been in business for over 20 years. We are your residential furnace repair experts. Call us today at 402-238-2425 for all your HVAC heating needs. We also service light commercial customers as well as geothermal units.
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