Thread: Range hood blows down

This Nutone NTM Premium range hood is vented straight out thru the back of the wall. The vent opens correctly when the fan is on. There are two fan motors in this model. The right hand fan draws air, as shown, very well. The left hand fan blows down, so hard it makes the flames flicker on the gas burners.
The fan must have been installed backwards. AFAIK, the only way to reverse the fan would be to flip the blades over, right? Anyone ever seen this?

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that is the austrailian model

and obviouslt installed by non pro which means all home circuits require inspection by licensed electrician

Originally Posted by John Kogel

The fan must have been installed backwards. AFAIK, the only way to reverse the fan would be to flip the blades over, right? Anyone ever seen this?

Flipping the fan blade will make no difference as its new orientation and direction will be the same.

Parts list shows fans as squirrel cage, same part for left and right fan.
Left and right fan motors are different parts. one spins CW, the other CCW.

Choices are: incorrect fan motor, internal/external wiring error, blocked air outlet (exhaust for that fan).

http://nutone.com/PDF/InstallGuides/NTMSeries.pdf

Bob Kenney
Independent Home Inspection

Originally Posted by Bob Kenney

Flipping the fan blade will make no difference as its new orientation and direction will be the same.

You sure about that?

Originally Posted by Bob Kenney

Parts list shows fans as squirrel cage, same part for left and right fan.
Left and right fan motors are different parts. one spins CW, the other CCW.

If that is the case, one sucks, one blows, if the fan is the same. That can't be right.

Originally Posted by Bob Kenney

Choices are: incorrect fan motor, internal/external wiring error, blocked air outlet (exhaust for that fan).

http://nutone.com/PDF/InstallGuides/NTMSeries.pdf

Bob Kenney
Independent Home Inspection

The air outlet is open to the exterior. And I can't picture reversed wiring making one motor spin backwards. I believe the fan blades are wrong. A propellor type blade can be reversed by flipping it, in my mind at least.

OK, there's no way you could install the fan flipped over, I see that now. There must be a left hand fan for the motor on the left, even though it is not shown in the parts list. At least now I can say it needs a new part. Thanks.

Originally Posted by wayne soper

that is the austrailian model

and obviouslt installed by non pro which means all home circuits require inspection by licensed electrician

This is a fairly new place. I think the non-pro work was done at the factory.

Originally Posted by John Kogel

A propellor type blade can be reversed by flipping it, in my mind at least.

Nope. Flip over a propeller blade and it still has the same pitch and direction. Reversing a squirrel cage blower will reverse the airflow. If the blower can be removed and reversed, then that is the solution. Otherwise, the blower motor needs to be different. I doubt that these motors are made to be reversible, so it would be a different motor. Might have been mixed-up during manufacture.

Originally Posted by Gunnar Alquist

Nope. Flip over a propeller blade and it still has the same pitch and direction. Reversing a squirrel cage blower will reverse the airflow. If the blower can be removed and reversed, then that is the solution. Otherwise, the blower motor needs to be different. I doubt that these motors are made to be reversible, so it would be a different motor. Might have been mixed-up during manufacture.

Thanks, Gunnar, you and Bob are right of course.

So answer me this. A double-ended skiff. If I take the outboard motor and clamp it to the bow, I've literally flipped the prop over, and the boat goes backwards. Right?

Originally Posted by John Kogel

Thanks, Gunnar, you and Bob are right of course.

So answer me this. A double-ended skiff. If I take the outboard motor and clamp it to the bow, I've literally flipped the prop over, and the boat goes backwards. Right?

Nope. The direction of travel is still away from the outboard in the direction of the bow. You've merely exchanged the bow for the stern of course you already knew that, right?

So. . . when you look in a mirror, left and right are reversed, correct? why aren't up and down reversed as well?

Bob Kenney
Independent Home Inspection

Flipping the blade does nothing, Either it's the wrong motor, or more probably the wrong fan blade. Reversing the polarity on an ac motor will not reverse the direction.

If it's a "convertible" hood, that is choice of internal or external exhaust, the orientation of air flow ( on some units) is changed by rotating the squirrel cage and its housing-along the axis, not flipping end for end. If the damper was positioned correctly for outside, but the fan was positioned for inside, the air flow would be "backwards" and push out through the intake vent. Check installation directions to confirm
..........Greg

Originally Posted by John Kogel

Thanks, Gunnar, you and Bob are right of course.

So answer me this. A double-ended skiff. If I take the outboard motor and clamp it to the bow, I've literally flipped the prop over, and the boat goes backwards. Right?

Um... right...

(psst, are you wearing that nice jacket with the reeeaaally long arms today?)

Originally Posted by Bob Kenney

Parts list shows fans as squirrel cage, same part for left and right fan.
Left and right fan motors are different parts. one spins CW, the other CCW.

Choices are: incorrect fan motor, internal/external wiring error, blocked air outlet (exhaust for that fan).

http://nutone.com/PDF/InstallGuides/NTMSeries.pdf

Bob Kenney
Independent Home Inspection

Bob, fans in this hood are not squirrel cage, just motors with fan blades. Think of a hamster on his wheel going nowhere---that's a "squirrel cage." Squirrel cage units are usually made with one motor in the center and the cages at each end. Swinging the unit around horizontally usually changes the direction of air flow from "internal" to "external"

This unit uses a common air flow, not ducting for each fan, thus no blocked air outlet is causing the problem.

John, was both motors running? If one was dead or "stuck" you would get the effect of one blowing out and one blowing in due to the air circulating around from the operating fan and being blown out the left one. Dis the air flows appear to be the same?

I would say---new motor time.

Rich

Originally Posted by John Kogel

.
The fan must have been installed backwards.

.
Problem Solved.
.

Originally Posted by Rich Goeken

Bob, fans in this hood are not squirrel cage, just motors with fan blades. Think of a hamster on his wheel going nowhere---that's a "squirrel cage." Squirrel cage units are usually made with one motor in the center and the cages at each end. Swinging the unit around horizontally usually changes the direction of air flow from "internal" to "external"

This unit uses a common air flow, not ducting for each fan, thus no blocked air outlet is causing the problem.

John, was both motors running? If one was dead or "stuck" you would get the effect of one blowing out and one blowing in due to the air circulating around from the operating fan and being blown out the left one. Dis the air flows appear to be the same?

I would say---new motor time.

Rich

Thanks, Rich. I felt at the time that the fan on the left was definitely working. On the high setting, it blows down on the gas flame. At the outdoor exhaust vent, the cover flap is vibrating like there's some turbulence. The possibility of one dead fan did occur to me later. Lucky for me, I don't have to design the repair - I just reported the deficiency and said - repair it.
I'm thinking a right hand fan motor fell into the left hand pile at the factory. They would look identical.
I wonder if the outer windings of the motor could be changed to change the rotation? Not that it matters much. My clients will likely just buy a new unit. The warranty was only for one year, too late now.

I'm reading this and distressed because I once could have explained the reasons and solutions for this problem.

More than 20 years ago I had reason to alter some pancake motors and I vaguely recall that by inverting the rotor I would change the direction of rotation.

Too much time and too many margueritas cloud my thought processes at this moment. However, I believe that a motor was improperly assembled. The fan maker may buy these from a subcontractor and have not reason to check actual performance as the Swiss and Germans routinely do. (Simulation testing sucks)

The driving motor must be changed or if the drive shaft projects from both sides then it can be reversed.

I often find vent hoods whose baffles are not correctly set for recirculating or exterior venting. Yeah it's the motor rotation.

Ace Home Inspections

I'm burned out and the gray stuff (in my head) has been doing research on this stupid screen for the last few hours and then someone writes "if your mug is left and right in a mirror on Thursday, then why is it not up & down on Friday" or something to that effect.....
It took the squirrel in the squirrel cage of my brain to finally figure out that it is because our eyes are next to each other as opposed to one on our forehead and one on our nose.
Oh! The Coffee's finally ready. Spel chek don't fail me now.

Originally Posted by bob smit

I'm burned out and the gray stuff (in my head) has been doing research on this stupid screen for the last few hours and then someone writes "if your mug is left and right in a mirror on Thursday, then why is it not up & down on Friday" or something to that effect.....
It took the squirrel in the squirrel cage of my brain to finally figure out that it is because our eyes are next to each other as opposed to one on our forehead and one on our nose.
Oh! The Coffee's finally ready. Spel chek don't fail me now.

Well if that were true, then when you lie down and look in a mirror (now your eyes are up and down) - how come your still only 'reversed' left to right in the mirror and not up and down?

Bob Kenney
Independent Home Inspection

Originally Posted by Bob Kenney

(now your eyes are up and down)

Your eyes are still not "up and down", your eyes are still "side-by-side".

So if I stand in front of a mirror, will I be able to play guitar like Jimmy Hendrix?

Originally Posted by Vern Heiler

So if I stand in front of a mirror, will I be able to play guitar like Jimmy Hendrix?

Yes ... if you can play the guitar like Jimmy Hendrix now ... the mirror should not stop you.

Originally Posted by Jerry Peck

Yes ... if you can play the guitar like Jimmy Hendrix now ... the mirror should not stop you.

There's always a caveat .

With a little more thought I can see it would not work anyway. The strings would have to reverse order top to bottom as well as make me left handed. Guess I'll have to keep the day job!

If there are right and left hand motors, there must be right and left hand fan blades. Might check to see which is the problem before replacing a whole motor.

Originally Posted by Kristi Silber

If there are right and left hand motors, there must be right and left hand fan blades. Might check to see which is the problem before replacing a whole motor.

And this is one of those lessons you never forget, after removing the fan blades and rolling them over like a monkey with a coconut, in front of the customer.

Originally Posted by Vern Heiler

The strings would have to reverse order top to bottom as well as make me left handed.

Yeah, keep the day job ...

By the way, the strings would be in the same order top to bottom, but, yep, you would look left-handed.

Originally Posted by Jerry Peck

Yeah, keep the day job ...

By the way, the strings would be in the same order top to bottom, but, yep, you would look left-handed.

Vern would have to start with a left handed Strat, and restring it so the low E was at the top, playing right handed. Then in the mirror, at least the guitar would look like Jimi's guitar.
That was one of the features of Hendrix's style. The bridge was angled wrong when he flipped the strings around. The whammy bar and the volume and tone controls were under his wrist.
Vern, just get a Beatle bass and you can be Paul McCartney. []

It worked! I turned my mirrow sideways and I was standing upside down, but maybe that's because it's Saturday hummmm

I have a hood fan with a similar problem. She's gone from suck to blow.

This is the fan assembly on the hood: http://Broan Range Vent Hood Exhaust...otor S97012248

It appears to be brand new. Any idea what I need to do to switch this thing around. I don't want my whole house smelling like the chicken livers cooking on the stove top.