We built our home and are having problems with the 48″ vent hood. It will pull a negative in the house and ashes from the fireplace 1/2 way across the room. Our a/c people went between theback splash and shelve of the vent hood with 2 12X12 grills and a damper on the outside of the house. It is wire with relays to the vent hood. The problem I have now is when you use the grill the smoke will be forced out and around the vent hood due to the force of air from the damper system. We have contacted GE with no help. Since we installed this vent hood I have read articles that talk about the power of these hoods and no return air. Have any of you ever had this as a problem.
BRM
Edited 5/25/2006 6:39 pm ET by brm
Replies
brm:
Correct me if I'm wrong but did you say that the hvac guys located the duct openings in the back splash area underneath the hood? If so, I have never heard of anyone placing them there.
With a hood pulling potentially 1200 cfm you definitely need make up air to prevent the negative situation you referred to. We install ours in an out of the way location in the same room as the range. We have put some in the toe kick area of the cabs, but most of the time we cut them into the floor (or wall depending on the situation) and use a regular duct cover so that they look like an hvac duct.
We attach them to mechanical dampers that go through the band board so there is no need for any type of additional wiring to operate them. I don't know what code requires where you are at but doing it this way works fine here.
You may want to check with your local municipality on what they will accept to correct your situation. I can't imagine that having two ducts in the back splash looks good, not to mention that it doesn't give you the result you are looking for.
Good luck.
sully
Thanks for the reply. A few questions I have. All the a/c vents are in the ceilings so if I went through the kick plate of the cabinets how does this air get tempered. Is this system tied into the a/c unit or a seperate system.
Thanks
I'm no expert on this subject, but had a thought - Could you run your supply air into the return air on your HVAC system? Then you wouldn't get concentrated flow like you do now.
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We had thought about the kick plate area of the cabinets. Your damper system, is it wired to the vent hood switch or do you turn on seperately. Someone sugessted that we install vent underneath the stove area, have you ever done it this way. Also, does the damper system need to be installed underneat the house or on outside of the house for the air it needs. I worry about the smell of the air sometimes under the house.
Thanks
BRM
It's way to large for any house unless you want to spit a pig or 1/2 beef in the house. I used to do air balancing as part of an Indoor Air Quality firm I managed. Small restaurants with deep friers, etc. only had 2000 cfm or so exhausts!!
Who designed this system and put it in?? They should be strung up for bad design!!
My thoughts exactly! I just designed the HVAC and Plumbing system for a new Dairy Queen Chill & Grill and the exhaust for the the 3-section deep fat fryer station is 700 cfm and over the griddle and charbroiler, the 4'x8' hood is exhausted at 3000 cfm. A residential hood, even the high priced semi-commercial yuppie versions, have no need for anything near 1200 cfm, though I doubt if it really passes that volume.
For the home owner, the first recommendation I would make is to cut the exhaust flow way back, like to 400 cfm, maximum. How to accomplish that? It depends on the exhaust fan/motor. You might be able to get an electriction to (or DIY if you have the knowledge/experience to do so) install a suitable speed control on it or it might need to be replaced.
Tim,
My fan has 4 speed with the 1200CFM's being the highest. Even hen it is used most of the time on 1 you still get the smell from the fireplace in the next room. The only time you really need to turn the fan to a high speed is if the grill is used.
When you talk about turning down the speed of the fan being turned down. Would that be the same as the using the #1 on the control.
BRM
Yes, that would be what I had in mind. Not a permanent fix, by any means, but you might try removing all of the ashes, cleaning it well and closing the firpalce damper. Won't solve the problem, but will eliminate the odor issue until the others can be resolved. Else, find a suitable window to partially open. Remember the path of least resistance, is always in effect.
In all of the magazines these unit are displayed. Our unit is GE Monogram. When I was looking all of the commercial/residential looking styles have this large of unit. I have been contacting GE with absolutely no help. Their comment is that they have never heard of this problem. I even filed a compliant with the better business bureau so that other will know in advance the problems they will have. I have had on person to tell me that they also use a damper system that is ran through the floor or the kick plate of the cabinets. I asked them how do you temper the air that would be coming in.
Thanks
BRM
I have a 54" range hood that is supposed to be rated at 1200 cfm. My makeup air comes from a 10" duct driectly under the stove. It is controled by an electric damper hooked to the exhaust fan. The hood is a Viking with a variable speed fan. The air is not tempered as it will be sucked straight up and out. No problems yet after 3 years.
I can't so anyone expecting to exhaust 400 cfm or more would not plan a makeup air system.
BRM,
If your fan is really operating at 1200 cfm, then you probably need a powered source of makeup air, not a passive duct. See this article:
http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/97/971104.html
According to the article, "A passive duct for a 200 CFM fan would require a duct 10 inches in diameter; a 300 CFM fan would need a 12-inch diameter duct. Downdraft range fans, which can exceed 600 CFM, aren't even listed in the guidelines. If it takes more than 20 in2 of opening area to alleviate the backdrafting, you probably need a fan-forced makeup air system."
Basically, 1200 cfm is huge, and causes all kinds of problems. Good luck.
I copied the articles you highlighted. This unit is a GE Monogram, it is amazing to me that GE can make a product that does not work adequately for the enviroment it is made for. GE has told me several times that they have never heard of this problem.
One response I have said that they had a 53" Viking and they put a damper system directly underneath the range. The hot or cold air did not matter since it came in and straight up thru the vent hood. With the highest speed being 1200 cfm's what size vent do you think this would have to have. Do you think this would work possibly.
Thank you for your help
BRM
To bring in 1000 cfm passively, you may need a 2 foot or more diameter duct. Other areas of the home are still going to be be experiencing a high negative pressure. A control interlinked, balanced, fan powered, make-up air system is what you need. Tempered or untempered air is your decision.
One thing that needs to be taken into consideration is that in the sealed space you have a combustion of 25 to 50k btu of gas, that would make the replacement air necessary, less than the fan exhausts.
But you are correct in that a non pressurized condition it will take more than a 10" replacement air vent. My unit has a 10" 4' pipe to the fan unit on the roof with a 1/3hp motor on the blower cage..
If the window is the closest thing to the hood its gonna provide most of the air that the hood exausts. and you dont use it for more than a half hour...
Bud
BRM,
If you know the name of the technical rep at GE who said, "We have never heard of this problem," I would be grateful if you could share it. Or at least provide the phone number you have been calling at GE. I'd like to talk to the people at GE to verify that they are really so clueless. It might make for an interesting technical article.
Martin Holladay, Energy Design Update newsletter
I filed a complaint with the Better Business Bureau, but the letter sent was not signed and I did not write his name down. The address on the BBB sheet is GE Monogram AP 6 Room 129 Louisville, KY . Another # I had called was Customer Relation 1-888-348-7563 and I talked with Kamora. We have had several problems with this unit and it just is 1 year old. I appreciate you wanting to talk with them cause comsumers need to know the negative points to these unit that are advertised so much in every magazine and cooking shows. Good Luck!
BRM
Being the one with the Viking hood I can only relay my experiences.I have a 10" duct with 1 90 and a total run of 6'. It begins right over the walkout of my basment. It is pasive in the sense that it doesn't have a fan mounted inside the duct.This morning I experimented to see just how things were working. I never run my hood at over 50% so in reading all these responses I decided to check just how it was working.I had no way of measuring the actual output. The exhaust run is 10 x 10" welded duct. It has 2 90s and the total run is close to 20'.Running the fan at top speed with all the windows and door to the basement closed the 'passive' intake would hold oak leaves I tossed up against the screen.My house doesn't have a fireplace and it is rf heated and the boiler is 3 doors and one floor level off the kitchen. Pulling air through the ac ducts would have just sent it in a circle. Speaking of which the air handler in my ac unit should be moving only 12-1500 cfm most of the time and it's 3 times the size of my exhaust hood fan. Granted it is just pushing/pulling the air in a circle.I doubt I was pulling a real 1200 cfm as I have built many commericial kitchens and the exhaust fans were much larger in size and most were only in the 1500 cfm range.I would guess in reality mine is closer to 8-900 cfm. I know it does a great job and beats the dickens out of most kitchen exhaust fans.One thing I don't understand is why your hood didn't come with a varriable speed fan?
Money? And the motor speed may not be able to be controled due to the motor design. Maybe one of the electrial types will pipe up on the subject.
The one I have has the Power/fan unit on the roof and does have a reostat type motor speed control. The only time is all the way up is when we are grilling something that is real smokey. Just heating the grill or normal cooking, its just on low.
Bud
GE is operating on the sell'm the biggest and best for the profit. Same principle that has so many V-8s still on the raod, needed or not, but the fan is only a component in the whole house system. The dsigner of the house is responsible for the combined effect of all the componenets, and we are still learning.
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"Basically, 1200 cfm is huge, and causes all kinds of problems. Good luck."When i read the title to this thread, I said to myself, 1200CFM IS the problem. I don't see morethan 600 neeeded in a home. There are stories of carbon monoxide poisoning from imbalanced systems like this!
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The wife says...open the window. Of course I hate this in the winter,or summer. I think you need a variable speed motor.
Yea, I have a 1000 cfm and a gas restaurant type grill. When I use it I crack the window thats about 5 ft away...
And I know the drill about having a fire in the fireplace in the other room and turning it on...Gets your attention..At least the furnace and h/w heater are in a sealed room vented to the outside.
Bud
If there is a louver on the outside of the home for your "makeup air", then you need to reduce the area of the opening by 50% to get the actual free area of the louver. A 12" x 12" hole has a free area of 144 sq in- about half that once the louver is added.
Same goes for your grilles on the inside. The number may not be 50% for the reduction in free area, but I bet it is at least 30%.
Now you have three potential sources of restriction just from grilles and louvers. Your electronic dampers should be fully open before the exhaust fan motor comes on- they have damper motors with limit switches built in.
You have a commercial exhaust system in a residential application. You will need commercial solutions to fix the problem properly.
Commercial hoods bring the makeup air to the hood above. There is either a perforated diffuser that runs the length of the hood on the outside, or there are secondary openings under the hood on the inside. The makeup air is usually tempered by a very large gas fired unit mounted on the roof. These units have sophisticated controls that modulate the gas valves according to the airflow drawn through the unit.
Your design is again flawed with the added makeup airstream being below the hood with the airflow parallel to the cooking surface. Makeup air under the stove would be better.
I would try to figure out how to get either a variable speed motor or some kind of mechanical speed control in there (either a rheostat or switches for multiple speed taps on the motor). Variable speed might be doable with a frequency drive, but that ain't cheap (and I do not know if it works on single phase power).
Lots of luck.
I have had some great ideas and suggestions. I thank you all, I wish I had gone this route in the very beginning of this problem.
Some of the suggestions I am not sure I understand exactly like: Variable speed fan (mine has 4 speeds) Even when I used it before the damper system was installed it would pull the fireplace smell in the room.
The damper system is free air without a motor and is wired with relays to each speed of the fan. On the outside it has a filter on the bottom and just 2 grills on the inside. The box on the outside is about 12" deep and 3' X 3' in size.
If we move the box damper system off the outside of the house to under the house and vent underneath the range what size grill would need to bring in enough air.
Thanks
BRM
Taking air from a vented crawlspace can be a bad idea.