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Old 12-08-2011, 09:06 AM   #1
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Inducer Motor "Flap"


What's that metal flap on the inside of the bell increaser for, in the opening of the inducer? It's screwed down and solid, no movement, and appears to cut about half of the air flow off.

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Old 12-08-2011, 10:39 AM   #2
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Inducer Motor "Flap"


I have a friend from a pro hvac site, who reomoved a couple orfices from his heating unit and had to restrict the flow down through the inducer blower to compensate for it.
I assume that a certain brand of furnace no matter what the size, probably comes with the same size inducer and they use the plate to compensate for certain btu inputs, or for however many burners the unit has.
Just my wild guess, dont know if it's right or not.

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Old 12-08-2011, 11:59 AM   #3
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Inducer Motor "Flap"


it increases the air pressure to get it thru the heat exchanger..even if you slide the supply fan out in your unit it has a fixed plate to narrow down the discharge air up thru the AC coil into the space
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Old 12-08-2011, 12:24 PM   #4
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Inducer Motor "Flap"


Maybe beenthere will come along and tell us, because now I'm curious what the real answer is.
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Old 12-08-2011, 12:40 PM   #5
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Inducer Motor "Flap"


Its to lower or raise the CFMs of the blower so the fumes will be removed properly. Have you seen a blower door fan, you can take off rings or add rings to change the air flow to move the house to 50 pascals so then we will be able to find air leakage. inducer motor has to exhausts flue gas and pre purges the heat exchanger so it will have to be set at the CFMs to pull the gases accordingly. hope this helps if not slap me
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Old 12-08-2011, 05:05 PM   #6
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Inducer Motor "Flap"


It is an orifice (sizing) plate and is specific to the BTU rating of the furnace. Sammy is right, some manufacturers use the same inducer for 3-4 different models.

Be VERY careful Doc when doing some of the ICPs as it has tiny little stubs that hold a plastic plate on and they break easy. If it breaks off then you can get pressure switch tripping problems.
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Old 12-08-2011, 08:32 PM   #7
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Inducer Motor "Flap"


My (possibly quite off?) thinking was that if it is to restrict air flow and I had a sticky or hard to close pressure switch than I could simply remove that flap and have more suction.??
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Old 12-08-2011, 08:46 PM   #8
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Inducer Motor "Flap"


no. high efficiency furnaces prove the CORRECT amount of airflow entering the burner for proper combustion as a function of the pressure drop across the heat exchanger. that is why you have 2 hoses/ports of different "WC ratings. pressure = flow =draft in our terms. the orifice is there to accurately control the draft amount according to what the design engineers designed. I can get into fluid dynamics as I did steam flows etc etc but that is way over your head. google "Bernoulli's principle" and study it if you can. You REALLY need to understand this stuff if you intend to stay in this business or be good at it. Draft is one of our MOST important fundamentals and they teach you about that in gas fitters school if you go for your gas license. Buy or borrow Fundamentals of Gas Utilization by John Dutton if you want to get serious about being a good gas tech. Then you progress into theory of combustion and how to setup burners etc. If not you end up being a parts changer and that is sad.

same principle applies to a mid efficiency furnace just they put the orifice in the downstream side of the ventor on some or measure the flow/pressure drop/differential thru the ventor fan rather than the heat exchanger. actually it is the heat exchanger as all the fumes/air pass thru it anyway.
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Last edited by yuri; 12-09-2011 at 06:38 AM.
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Old 12-08-2011, 08:53 PM   #9
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Inducer Motor "Flap"


For this particular case I was wondering about on an 80% gas furnace and an old one, Consolidated.

I've changed both the inducer and the pressure switch and the system is running fine, I was just wondering if it could work.
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Old 12-08-2011, 09:28 PM   #10
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Inducer Motor "Flap"


its illegal and dangerous and U could get sued.
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Old 12-08-2011, 09:40 PM   #11
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Inducer Motor "Flap"


Quote:
Originally Posted by Doc Holliday View Post
My (possibly quite off?) thinking was that if it is to restrict air flow and I had a sticky or hard to close pressure switch than I could simply remove that flap and have more suction.??
It restricts the inducer so that it doesn't create more draft through the heat exchanger then its designed for. Many manufactuers use one size of inducer to fit many different BTU furnaces, and only control the draft through the heat exchanger with the restricter plate.

Do not remove it to make a furnace work. If a pressure switch isn't closing. Find the real problem.
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Old 12-08-2011, 09:54 PM   #12
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Inducer Motor "Flap"


It turned out that after a new pressure switch was not closing, I put my manometer onto the draft motor and it wasn't pulling enough inWC to close it. Ran to the supply house for a new one.

I put the flap on the new one but the entire ordeal left me wondering had I just removed that flap from the old inducer could it have worked, that's all. Now I know why it's there, thanks.
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Old 12-08-2011, 09:59 PM   #13
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Inducer Motor "Flap"


FYI some aftermarket inducers run 200 rpm less than OEM ones and that can be slow enough to cause a problem. Had a Ducane OEM at 3400 rpm and the rotom aftermarket at 3250 and it would not work. got the OEM and no problems. OEM Rheem ventors for mids are higher rpm than some aftermarkets too. carefully look at the rpm rating on the motor and you may be surprised.

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