No idea why it's blowing and not sucking, but flexible duct is a really bad idea - most likely against code and dangerous - grease can get trapped and catch fire.

Flexible ducting also causes noise levels to increase greatly, restricts air movement so your CFM's will take a hit.

The only thing I know is the blower is running in reverse, either due to installation or wiring etc.

was the fan motor mounted upside-down?

If the vent exit is blocked it can make a blower feel like it's running reverse.
one way to semi recognize this is 600 CF would seem like a tornado on your range top if it was installed upside down. If the if the air seems a lot less than this I would look at damper blockage as the issue.

Thank you for all these helpful suggestions. We didn't think the fan motor was upside down because it used to blow up into the cabinet before he hooked up the venting. We will give service a call since our contractor insists it is all done correctly. We will either get this resolved under warranty or else resolve the installation error.
Other than that, the kitchen looks lovely! Thanks again.

I don't know how the transitions, dampers and outside caps are configured on KA hoods, but having had a VH miss-installed that did pretty much the samething, I'd follow Jakvis' suggestion on checking the dampers. There usually are dampers where the exhaust blows from the motors. If they were blocked from opening when the ducting was installed then the fan may be blowing against the closed dampers which would give the appearance of blowing in the wrong direction and would be noisy as hell. Two different causes are that flex ducting may be stopping the upward travel of the dampers (especially the "accordian" style or the screws that anchor the ducting to the transition may be too long and are blocking the normal opening of the dampers. on VH, dampers are opened by the exhaust flow. One other possibility is that they were damaged during the install. Other than polarity instalation mistakes, electric motors rarely fail. Other than duct tape, what required sealant? It's also possible your outside vent cap could be stuck as that could give you enough back pressure to keep any internal dampers closed.

Yes everyone likes the metal vent pipes, but really there seldom used any more. While I doubt that would be the problem, I guess if it was installed badly so that it kinked, and the air couldn't get through, it could blow back.

I found on mine, that it seemed to be blowing down, but when I checked the outside vent air was coming out. I went back in and took the fan out of the hood,and saw that the spring loaded "flapper" right at the on the top (mine was top mounted) was keeping it partially closed. I had to prop it open.

Tested it and it sucked a light chunk of paper right up, and outside it seemed more air was coming out. I still found though at the very front of the unit there is a bit of a down draft (over where the light is mounted). Still the paper is sucked right up against the mesh filter without me holding it, so it's working for me.

You might want to check that that flapper is OK.

A recent thread
Stove Ventilation Blowing into Kitchen
in another forum.

Here is a link that might be useful: Stove Ventilation Blowing into Kitchen (remodel forum)

I know this is a really old post, but since I found it while solving the same problem, I thought I'd let others know.

First, I have a Vent a Hood with dual squirrel cage fans. When on, it seemed to blow air back down to the range and into the room. Very strange. If you have a dual motor vent, you may need to swap the two motors.

It turns out that I installed the two squirrel cages incorrectly. One is red and one is white: I originally put the red one on the right side and the white one in the left side. When on, the red one spun counter-clockwise and the white clockwise. This had the effect of moving air *away* from the duct, which runs up between the two fans.

I swapped the two, and then they sucked air up right away. This had the effect of pulling air into the duct.

I'm having the exact same symptom with my new Sirius Rangehood. It's because it was installed incorrectly. Usually due to 1 of 2 incorrect installations:

1) When shipped in the box, the fan housing is sometimes packaged in reverse, to seal it off from anything getting inside while in shipping. When unpacked, it of course needs to be reversed again to install in the correct orientation.

2) The wiring was hooked up backwards and polarity is reversed, thus the fan blades are turning in the wrong direction, blowing air into the house instead of out!

I have a 20 year old BEST chimney range hood that has always worked perfectly. However, we has a bad storm a week ago, lots of wind, and now the hood is blowing in instead of pulling out. Any ideas on what needs to happen?

Could it be that you now have a chimney blockage from the storm? The fan exhaust now has no where to go but back into your kitchen? Have a qualified chimney sweep inspect the stack for blockage.

I would guess a damper door is jammed shut for some reason. You may have one outside, and one at the hood. Both should be checked for free movement.

I will do that...thank you!

I fixed a kitchen fan exhausting to the outside (yes, always smooth metal - never corrugated). I found that there were very small areas in the fan housing ((that faces the top of the stove) that were not sealing at all ..... since they just wanted it fixed without having to by a new fan I simply used some sticky (back pressure it is called) one side aluminum tape and put small bits around the small holes that were allowing air to be pushed back towards the stove. The sticky aluminum tape did a great job - I didn't stop until there until all the leaks were plugged. It was leaking just about everywhere. I was tempted to get a caulking gun out! She was happy, I was happy...... on another note...many homes do not have air coming into the house! With new high efficiency furnaces (gas) the installers have used the hole at the top of basement foundations to install the 2 furnace vent and intake pipes. Now that they have sealed off that former fresh air vent...many homes no longer have fresh air coming into their home..... no air coming in....no air going out. It was a townhouse and the refused my request to have fresh air enter the home.......?really?.... so I put a covered and filtered vent over a small basement window (all metal with a heavy metal screen to stop creatures as well. I found just having a 2 inch or so opening allowed plenty of air into the house. It was a simple fix.....bit cool in the winter... but with a filter it was actually one step up from the old 4 inch circular hole in the upper foundation.

A two-inch filtered opening for MUA will lead to significant pressure loss for any useful hood flow rate that will be revealed if one measured the flow rate of the hood or the house pressure. Even if the combustion appliances have their own MUA, too much restriction on the kitchen ventilation MUA will degrade hood performance.

I have the same problem with the range hood I found out why is blowing dawn if you have blowing staith up will work ok but blowing to the side and up you need blowing weel I would like to know who is selling range hoods with blowing weel

A hood blower operating into a bend will see more pressure loss than blowing into a straight duct. This has to be accounted for in selecting the blower rated CFM. If the flow has to be directly out the back of the hood, then either a remote blower should be used, or a blower intended for that purpose sold with the hood. Contact the candidate hood company for compatibility information.

Reverse the polarity or swap the white and black power wires. Turn off the breaker first!

Reverse polarity can make the fan blow in not draw the air out.

Most of the time all you have to do is take the blade off, flip it over and reinstall it.

I used the semi-rigid flexible duct as an adapter to connect to the steel exhaust and had the same problem with it blowing air. I was able to fix it by placing my hands on each side of the flexible duct about 6 inches above where the hood and duct are connected. I moved the duct in a circular motion while the range was on and heard a click. After the click air had started sucking and no longer blowing.