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Stove Ventilation Blowing into Kitchen

Posted by mminmi (My Page) on
Thu, Mar 31, 11 at 8:30

I contacted my contractor at the beginning of November with this issue... it is still not resolved. No one (including Zepher customer service and the Zepher service man) can seem to figure out what is going on.

We had our kitchen renovated last year and are having problems with the exhaust fan. The contractor installed a Zepher AK8100AS (600cfm on max). Here is the situation... We have 8 foot ceilings. The vent hood is installed inside the cabinet above the stove and is 39.5 inches above the cook top. The exhaust exits the top of the unit in a 6" pipe (runs 12 inches), makes a 90 degree bend (perpendicular to the wall the stove is on) in the ceiling, runs to the next joist opening (18 inches ish), makes another 90 degree bend and runs 4 feet (parallel to the stove wall) to the outside of the house. There is what looks like a large dryer vent on the outside of the house with a single flap and a triangular shield. The only joint I can see in the cabinet is a joint... no screws or tape. I don't remember what is in the ceiling, but am fairly certain it is 6 inch pipe. The equivalent run is 67 feet, the manual say it needs to be less than 100 feet.
The vent is really loud when it is operating, and there are no appreciable differences in sound between the 3 speeds (the spec sheet gives the range of 1.4 - 6 sones for L/M/H). The vent appears to be blowing into the kitchen. When I light a candle and hold it up by the fan, the flame dances around, it isn't being pulled. It feels like air is blowing in when I put my hand next to the grate, and it will not hold a piece of paper against the grate. When I set the candle on the stove and blow out the candle, the smoke 'wallows' around and eventually dissipates into the kitchen... it isn't sucked up. The vent flap on the outside of the house opens when the fan is on.

The manual specifies the hood to be mounted 26-36 inches above the cook top... we are too high, but that should not be an issue if I am holding a candle close to the fan.

The Zepher service man says the hood is operating correctly and thinks it is an installation issue.

Zepher customer service thinks it is a ventilation issue... they say the ductwork must have been downsized to 4 inches I remember 6 inch ductwork... trying to figure out a way to see if it was downsized without knocking a hole in the ceiling....

Installer can't figure it out and need parts from the cabinet installer to lower the unit before he can start trouble shooting...

Another retailer suggested that with the two bends so close together there maybe some flow issues causing some of the air to blow into the house and some out of the house.

Does anyone have any thoughts?


Follow-Up Postings:

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RE: Stove Ventilation Blowing into Kitchen

Has anyone checked the filter? If there is a protective wrapping on the filter, no air flow.


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RE: Stove Ventilation Blowing into Kitchen

Yes... no wrapping. The situation is the same when I remove the filter. I was also able to confirm with the origonal installer that 6 inch pipe was used.


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RE: Stove Ventilation Blowing into Kitchen

The pipe joints should have been taped.

Greasy air WILL leak out and stain anything nearby.

It really sounds like the line is blocked or the length is excessive (regardless of what the manufacturer calls out as a 'maximum length').

"The vent is really loud when it is operating, and there are no appreciable differences in sound between the 3 speeds (the spec sheet gives the range of 1.4 - 6 sones for L/M/H)."

Even with a fan operating near stall you should hear some difference in fan speed.


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RE: Stove Ventilation Blowing into Kitchen

If flexible ducting is used instead of rigid, performance can be halved.

And the general rule is that each 90 degree bend reduces flow by half. Two abrupt bends close together. No wonder there's hardly any air flow.
Stove Exhaust
A bend or two too many.


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RE: Stove Ventilation Blowing into Kitchen

I would suspect the ducting.

Have your installer pull the hood and verify operation of the hood itself. That is, if you wire it up and turn it on, what does it do? If you get a low, med, and high operation with a obvious change in suction with speed change, then I would rule out the hood as the issue.

If the duct must run where it is, you may need to change the duct size, configuration, or add a power exhaust to help pull the air through the duct. Your contractor could contact an hvac parts distributor for assistance in ductwork calculations if that is needed.


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RE: Stove Ventilation Blowing into Kitchen

Hoods are almost never ducted properly, unless the install is dead simple. It's a safe bet that your duct is crushed, bent, or constricted.


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RE: Stove Ventilation Blowing into Kitchen

"If flexible ducting is used instead of rigid, performance can be halved. "

Flex ducting is not allowed for hood exhaust lines.

Solid metal duct only.


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RE: Stove Ventilation Blowing into Kitchen

"If flexible ducting is used instead of rigid, performance can be halved. "

See link citing study that shows flexible duct performance drops 4-10 times published values.

Flex ducting is not allowed for hood exhaust lines.

Depends on the governing Code. It is allowed in the one I work under. OBC 9.32.3.10. (6) only requires it be non-combustible, corrosion resistant, and lead directly outdoors with no connections to other exhausts or ducts.

Here is a link that might be useful: Flexible Ducts


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RE: Stove Ventilation Blowing into Kitchen

Okay, the conclusion seems to be the 2-90 degree bends are too close together. I will find our for sure when they disconnect the fan and report back.

The duct run is as follows:
Vent Exit ->
12 inch (approx) 6 inch diameter duct ->
90 degree 6 inch diameter elbow (the turn takes the run perpendicular to the wall the stove is on) ->
4.5 inch (approx) 6 inch diameter pipe->
90 degree 6 inch elbow (turns the run parallel to the stove wall) ->
54 inch (approx - max) 6 inch diameter pipe ->
6 inch wall cap with damper

The contractor seems committed to getting this exhaust fan operational and thinks the best solution may be to install a remote fan. Does anyone know of a good resource to learn about remote vent fans?


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RE: Stove Ventilation Blowing into Kitchen

best solution may be to install a remote fan

I think you'll have the same key problem: restricted ducting. Check all the other possible detriments to proper operation mentioned by the posters above.

Perhaps Fantech customer service can be of help. I've looked at their equipment, but have never installed remote fans myself.


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RE: Stove Ventilation Blowing into Kitchen

mminmi please link to the Zephyr model on the web.


here is another test you can run without ripping anything open.
1/ run it on high then on medium speed, after opening a window to ensure you get a lot of "easy" replacement air;
2/ run it on high then on medium speed, after closing all windows doors and air leaks, to see what it does when replacement air is not available;
3/ compare the two situations. (noise generated, adn suckage).

your ducting is quite short length overall.
of course, with the two bends it runs an equivalent length that is longer.

it is an easy out to say golly the bends are close to each other. beware of premature conclusions.


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RE: Stove Ventilation Blowing into Kitchen

Hi Davidro1 -

I attached the link from the Zephyr website. I ran the test you outlined above and did not see or hear any difference with the window (or doorwall)open vs. closed. In both cases I tried to get the fan to 'suck up' an envelope, a plastic grocery bag and a piece of paper. None of them stayed up... they were all 'blown' down in both cases.

Attaching some pictures... I hope! Okay, gotta figure that out...

Here is a link that might be useful: Zephyr Tornado1


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RE: Stove Ventilation Blowing into Kitchen

Hopefully this works...

If not, then the link to photos is attached...

Here is a link that might be useful: Pictures of Range and Hood


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RE: Stove Ventilation Blowing into Kitchen

Here are the pics:

Front View:
Front view of hood and range

Angle view:
Stove and Hood angle

Side View:
Side view of hood looking to back of house

Zephyr unit (Below) - Blue Tape is lowest mounting position:
Zephyr Unit

Zephyr Unit in Cabinet Hood:
Zephyr Fan Unit


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RE: Stove Ventilation Blowing into Kitchen

This is a though.
Is it possible that the fan will rotate the other direction if your installer switches the connection of positive and negative? Large commercial HVAC systems do this....just a thought......


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RE: Stove Ventilation Blowing into Kitchen

Thanks juliekcmo, I had the same thought. The Zephyr service man ASSURED me that the fan was rotating the correct direction. The GC is due here next week... hopefully we will have a better understanding what is going on when we can drop the fan and install it at the correct height.

If this does end up being an issue with the duct work, we are looking at taking cabinets down at a minimum. The centerline of the duct is 16" off the stove wall (runs right along the front of the hood cabinet. Probably drywall work which means repainting the ceiling... not sure about the backsplash.

My gut is saying that it is either the height of the fan unit the air is hitting the first turn too soon, and/or the two 90 bend are too close together.

Will let you know what we find next week.
The ductwork is new, and I saw the installation before it was drywalled up. I am confident that we have solid ductwork (no flex stuff) and is not crushed at all.


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RE: Stove Ventilation Blowing into Kitchen

The fan connects to a standard 15-20 amp branch circuit. This is not positive and negative, it is live and neutral and even if they are flipped the fan will operate the same way. The motor has to be designed to reverse in the first place or be altered to do so.

The problem was pinpointed in the OP: there is only 4.5 inches between two 90 degree bends. Your installation is not much better than the mess in the pic in my first post. Believe me, I'm not puzzling over why that stove exhaust barely pulls any air.

The installer is just trying to put off fixing what he made a mess of in the first place.


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RE: Stove Ventilation Blowing into Kitchen

In the OP it says
"... runs 12 inches), makes a 90 degree bend... runs to the next joist opening (18 inches ish), makes another 90 degree bend and runs 4 feet ..."

mminmi, using thin plastic like sandwich wrap or the kind you get with dry cleaned clothes, cover the area of the mesh filters and report back about the suckage. At the lowest speed you should be able to sense the fan pulling air, or not.
The reason i ask for this is here:
"The vent appears to be blowing into the kitchen. When I light a candle and hold it up by the fan, the flame dances around, it isn't being pulled. It feels like air is blowing in when I put my hand next to the grate, and it will not hold a piece of paper against the grate. When I set the candle on the stove and blow out the candle, the smoke 'wallows' around and eventually dissipates into the kitchen... it isn't sucked up. The vent flap on the outside of the house opens when the fan is on."

This is confusing, and you need to figure out once and for all if air is moving through the vent conduit. Several different kinds of tests. The thin plastic test is just one test. Another one is to watch outside the house if the colored smoke come out when someone produces harmless colored smoke under the hood.


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RE: Stove Ventilation Blowing into Kitchen

Let's see if this works... trying to post the video.
Photobucket

Davidro1 - I did as you asked with interesting results. Low medium and high exhibited the same behavior.
1) I covered the outside of the filter with sandwich wrap, reinstalled and turned on the fan. The wrap was sucked up against the grate. The fan was noticably quieter and I could hear a difference between fan speeds.
2) See video - I taped the wrap to one side of the filter opening it seemed to wallow around, when I 'directed' the wrap towards the fan it then sucked the wrap.

What type of colored smoke do you suggest...


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RE: Stove Ventilation Blowing into Kitchen

Davidro1

Ok, it was a latter post and is not altogether clear.

The duct run is as follows:
Vent Exit ->
12 inch (approx) 6 inch diameter duct ->
90 degree 6 inch diameter elbow (the turn takes the run perpendicular to the wall the stove is on) ->
4.5 inch (approx) 6 inch diameter pipe->

The video indicates the fan is not creating a strong enough vacuum--likely because there are too many turns. That the exterior flap still opens doesn't mean the fan will clear combustion particles.

An airflow meter or pinwheel anemometer can be used to measure fan power.


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RE: Stove Ventilation Blowing into Kitchen

To clarify my shorthand:
The vent exits the fan unit, into
a 6 inch diameter duct approximately 12 inches long into,
a 90 degree, 6 inch diameter elbow into,
6 inch diameter duct approximately 4.5 inches long...

worthy - is it too many turns (only 2), or is it that the turns are too close together, or is the first turn too close to the vent exit?

I am trying to figure out how to reroute the vent. from the construction picture (from 20 years ago) it looks like we will run into a drain and heat duct as we go over and out above the window....
Photobucket


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RE: Stove Ventilation Blowing into Kitchen

the paragraph I quoted showed we don't even know if the unit was installed with a cover over the exhaust preventing any and all air from moving through the ducting.

mminmi that saran wrap video showed, for a split second only, the saran wrap placed over the grill. Not a lot of time.

Tape newspaper over the front and turn the fan on.
Then, start ripping open the newspaper and notice if air is being sucked in.

I'm sure you have already called Zephyr several times.
Please report here what they are telling you.


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RE: Stove Ventilation Blowing into Kitchen

Hi Davidro1 - I'm not sure where you would like the newspaper taped... to cover the filter opening or hanging down from the filter opening. Let me know, and I will give it a go when my camera girl gets home tonight.

The owners manual does not specify anything on ducting other than to calculate equivant length and say that the bends should be as far apart as possible. Here is the chain of correspondence I've had with Zephyr after I had contacted Customer Support on the phone and the service man came out:

Hello Zepher -

I contacted my contractor at the beginning of November with this issue... it is still not resolved. No one (including Zepher customer service and the Zepher service man) can seem to figure out what is going on.

We had our kitchen renovated last year and are having problems with the exhaust fan. The contractor installed a Zepher AK8100AS (600cfm on max). Here is the situation... We have 8 foot ceilings. The vent hood is installed inside the cabinet above the stove and is 39.5 inches above the cook top. The exhaust exits the top of the unit in a 6" pipe, make a 90 degree bend (perpendicular to the wall the stove is on) in the ceiling, runs to the next joist opening (18 inches ish), makes another 90 degree bend and runs 4 feet (parallel to the stove wall) to the outside of the house. There is what looks like a large dryer vent on the outside of the house with a single flap and a triangular shield. The only joint I can see in the cabinet is a joint... no screws or tape. I don't remember what is in the ceiling.

The vent is really loud when it is operating, and there are no appreciable differences in sound between the 3 speeds (the spec sheet gives the range of 1.4 - 6 sones for L/M/H). The vent appears to be blowing into the kitchen. When I light a candle and hold it up by the fan, the flame dances around, it isn't being pulled. It feels like air is blowing in when I put my hand next to the grate, and it will not hold a piece of paper against the grate. When I set the candle on the stove and blow out the candle, the smoke 'wallows' around and eventually dissipates into the kitchen... it isn't sucked up. The vent flap on the outside of the house opens when the fan is on.

The manual specifies the hood to be mounted 26-36 inches above the cook top... we are too high, but that should not be an issue if I am holding a candle close to the fan.

The Zepher service man says the hood is operating correctly and thinks it is an installation issue.

Zepher customer service thinks it is a ventilation issue.

Installer can't figure it out and need parts from the cabinet installer to lower the unit before he can start trouble shooting...

Another retailer suggested that with the two bends so close together there maybe some flow issues causing some of the air to blow into the house and some out of the house.

Can you help me resolve this issue?

The response from Zephyr:

From what you are describing, its almost 100% guarantee to be a duct issue. If the duct, as you say, is 6 inches on the hood, we would need to determine if the duct is 6 inches in diameter, all the way thru. We have had issues to where installers will reduce the duct size between the hood and its exit point, down to 4 inch diameter. The best way to determine if its a hood issue or a duct issue, is that the duct will need to be disconnected at the hood, and then the hood turned on. This isolates the duct run from the hood. The main issue that you describe is all 3 speeds sound the same. this is 100% issue with the duct, most likely being reduced in size. When this happens, the hood will be noisy and air will actually blow downward back into the kitchen. When the hood is on, it is trying to force a very large amount of air thru the duct. if the duct is smaller or reduced in size, it is trying to force 6 inches of air thru a smaller opening, which it cannot do. that excess 2 inches of air has no where to go but back down thru the hood into the kitchen.

My response:

Thanks for your quick response. I am fairly certain that there is 6 in duct work in the ceiling. The flap on the vent on the outside of the house is 6 inches in diameter, and the venting that sat in my kitchen. I am attaching a picture of the venting sticking out of the ceiling and the vent piece going through the wall before it is installed...
What about the short distance between the 2 90 degree elbows?
Any other ideas?

Zephyr response:

if possible, please out line the entire duct run, how many feet inbetween turns, basically from start to finish. As for distance between elbows, there needs to be atleast 1-2 feet inbetween any type of turn

My response:

Just confirmed with the contractor that the ducts are 6 inches in diameter... That was the last thing the installer did on my job and has the receipt showing he purchased 6 inch duct work.
The duct run is as follows:
Vent Exit ->
12 inch (approx) 6 inch diameter duct ->
90 degree 6 inch diameter elbow (the turn takes the run perpendicular to the wall the stove is on) ->
4.5 inch (approx) 6 inch diameter pipe->
90 degree 6 inch elbow (turns the run parallel to the stove wall) ->
54 inch (approx - max) 6 inch diameter pipe ->
6 inch wall cap with damper
The installation manual does not specify distance between turns. If the best way to determine if the hood or duct work is at fault is to drop the hood, why didn't the Zepher service man do that?

Comments?

Zephyr Response:

We see that the issue is most likely the 4.5 inch between elbows. It is always best to have ateleast 1-2 feet inbetween elbows. Being that 6inch is the minimum size, if you are to keep that run, you may have to increase the diameter of the duct to 8-10inch to possibly eliminate that restriction.


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RE: Stove Ventilation Blowing into Kitchen

Good idea, video.

Tape newspaper over the entire front in order to block air from coming into the hood.

Then turn the fan on.

Within 3 or 4 seconds you may get the feeling that air is moving around inside your hood but that the hood is not sucking new air in because it doesn't need it, because maybe the entire duct is blocked. If the blower really sucked air and if the duct were really open, the newspaper would be pulled tight against the grille when you turned the vent on. And it would be possible to see that. But don't draw any conclusions yet. Maybe a little bit of new air is indeed being pulled in, but not much.

You did write "The vent appears to be blowing into the kitchen... " so let's figure out if the blower is turning in the right direction and is pushing air into a tube that IS open, not blocked. Maybe it's pushing air into a blocked tube, and so you get occasional backdrafts and "air pulls" as the system pushes air into a dead end.

So, you've blocked the grille, and you've turned the power on, and you've seen whether there appears to be a sucking force, and then _After_ 4 or 5 _seconds_ then start ripping open the newspaper. You will see very clearly how much new air is being sucked in, now, when you provide a small opening for air to enter.

The other way of holding the saran wrap or paper is not going to show much. To hold something a few inches away and observe it, the best thing might be a White smoke to show more easily if air is going into the hood.

The noise is high, which often means that the blower is pushing against air that is not moving, not cooperating, with nowhere to go. Your duct ("tube") may be blocked. But don't draw that conclusion either. Let's see how much real suction is visible, and feel-able.


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RE: Stove Ventilation Blowing into Kitchen

it's been 4 days including a weekend.
Diagnosing the problem is like a Fifth Grade science project.


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RE: Stove Ventilation Blowing into Kitchen

worthy - is it too many turns (only 2), or is it that the turns are too close together, or is the first turn too close to the vent exit?

The best route is the direct route. But that 4.5" run between two turns is the killer. Speaking of 5th grade science projects, try the equivalent with a couple of flexible straws and two strong lungs and you'll see.

I hope you still owe the installer payment!


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RE: Stove Ventilation Blowing into Kitchen

To the OP: here is an example of the _Amount_ of video that is necessary to illustrate a problem. About 20 to 30 seconds per problem. It's two minutes long.

Here is a link that might be useful: Crazy-things-that-pass-inspections


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RE: Stove Ventilation Blowing into Kitchen

Mystery Solved! It was the installation. The contractor dropped the fan unit and found the butterfly valve on the unit was not taken out of the shipping position. There are two stops that the wings are trapped behind. See here:
Photobucket
When it was installed properly, the air flowed (no surprise).
Vent Fan After

I had him lower the unit 7 inches (to provide some distance to the first bend, and put the switches in a better position. On low the unit is now VERY quiet, and it will draw a piece of paper within 4 inches to the filter. On high it is amazing how quickly it can exhaust cooking fumes and smoke. This is what I wanted...
Sorry for the delay in responding, we were out of town last weekend and my 6th grade videographer has had a bunch of (science) homework...


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RE: Stove Ventilation Blowing into Kitchen

good deal!
my first thought was the back draft damper
second was too many restrictions..
worthy gave you very good advice.

glad you got it solved, and thanks
for sharing your issue with us all.

best of luck.


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RE: Stove Ventilation Blowing into Kitchen

Thanks to everyone for their help! Learned alot about HVAC in the process. Hopefully this post will save someone alot of time in the future as well!


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