hood problem

Joined Jun 14, 2015
Hi - a bit concerned about managing cost of hood running all day. (its 10" ft)

I haven't gotten my utilities in yet what am i facing?

Also its noisy any way to reduce the sound down a bit. (would the noise be in the upper part or lower, i can't tell.

Joined Dec 21, 2012
Hope you get some answers.  I have two 10-footers and I never have been able to figure out the best way to go.  Sucks cold air out of the dining room like a giant vacuum cleaner.  Have had several "experts" check the make-up air and the out-going air to try and match them over the years.  One says use a wind meter sort of gizmo, another says matching the amp draw on the two motors is best.

Maybe someone can help me as well.
Joined Jul 28, 2001
Hey @mundawgs79  ,

I am in no way an electrical person. I did address this a while back.

A 10 footer probably has a 3/4hsp motor approx 3K cfm

I think mine was

                draws 5 amps

115 volts X 5amps = 575 watts

my electric charge  .07.2 from the provider

575 watts X  24 hours =  13,800 KWH

13,800 KWH  X  07.2 cents charge  =  99360 cost to run 24 hrs. would be  $9.94 a day to run

That is the exhaust fan.  You will also have a make-up air fan

Maybe someone will come on to explain and make sense.
Joined Oct 31, 2012
Mundawgs79- What kind of noise? There should not be a lot of noise. the rush of air like you would hear with an ordinary large fan perhaps but no rattling or other mechanical sounds.  

A couple of things.

     I would first suggest someone who has recently installed a modern air system, set up for the current codes in your area or the current codes in a more regulated area. As various agencies learn new things, the regulations change. Here in NY, they seem to change regularly. So what was "normal" as little as five years ago may be outdated already. 

     After repairing a faulty hood once, it started working well for the first time in years.  Unfortunately, this meant sucking the air out of the dining room, killing the air conditioning. 

     In response we made sure several kitchen windows were open while the fan was on so the hood could draw enough air without affecting the dining room. In winter this made things a bit cool in certain areas of the kitchen but kept the dining room at appropriate comfort levels. In summer we kept both kitchen doors open as well as the windows.   We also turned the hood on as late as possible and shut it off as quickly as possible after service.

     When we sold the place, the new owners were told they would have to redo the hoods, precisely because of the new make up air regulations. I never got an answer as to what they were. 

    I tried to figure out what the standard was for make up air and like Railbeaux, I got several answers. So what I learned was that the air has to come from somewhere. If the hood is moving 200 cubic feet of air per minute, then you need somewhere for that much replacement air to come from. If you can't open a door or two connected to a non dining room area, If you can, install a couple of windows, even small ones. Ours were more like transoms, set high along the rear wall of the kitchen. 

     In doing further research, I would suggest going to any company who installs hoods in hotels. Hotel kitchens don't typically have windows and have multiple conflicting systems and the resulting issues. Designers and installers for those systems have  to over come the same problem you describe. The fire insurance companies should also be able to help as they are the main ones concerned with a poor hood system. 

      I planned to fill the kitchen with colored smoke to be able to actually see what the air was doing. I did not decide on a way to do this before we sold but my original plan was to use colored smoke grenades like they do on July 4th. A large bunch of incense might do the trick as well. 

    Whatever you come up with, keep us informed please. This is one area I always wanted to know more about. 
Joined Dec 21, 2012
My hoods both have make-up air, with separate make-up air fans up top next to the hood fans.  This is what the service guys were trying to match.  Like I said, the last one tried to match the two amp draws from the exhaust fan and the make-up fan, while the first one tried to match the two airflows with his widget.
Joined Jul 28, 2001

The amp draw thing doesn't seem quite right. From what I can remember from mine now and in the past the exhaust and makeup air fans are two different animals. I now have a down draft for the hoods with large fan like blades and my makeup airs are a small squirrel cage type fan. I remember the technicians using these upside down cloth-like tents to measure the CFM for the makeup air. They did replace the squirrel type intake fans with  more powerful ones. I kind of remember them telling me that the specs they had to go by on the fans themselves is all they had. The actual match in air will be different a lot of the time depending on variables. The cleaning and maintenance of the hood, different pressures in air. If the ovens are not properly working and emitting gas, the gas rises and passes through much faster I think? because the gasses and the other contaminates from the constant burning of gas are lighter and buoyant. Sorry, I'm in over my head now.
Last edited:
Joined Apr 5, 2007
From my experience there is always going to be a bit of voodoo when hitting your make up sweet spot.  Air flow, even in a small place is a complicated affair and even really solid installers (or engineers, as we had to call in with one place I helped open) will often need to "play a hunch or two" to really nail it. In a new place the theoretical balance will really get tested by what you are using by way of appliances.  Venting out a smoker caused real headaches for example, as the smoke and airborn grease were factors local installers had never encountered before.  

Not sure what you mean by noise, can you describe it? 
Joined Jul 28, 2001
Many, many, moons ago when I finished out  and also on a remodel it seemed the Hood vendor or the technicians, installers, salesmen,etc. would not field any questions about air movement or efficiency of the unit. They always referred me to the architect. And she always told me that her main responsibility was mainly code compliance. I wonder if there is any type of architectural information online that may help.

Unfortunately for me, Texas summers are hot and we usually have the ovens fired every hour we are there during the day. The ambient temperature within the ovens aura is quite high. I really did not want to upgrade the hood. In turn, I installed an extra 10 tons of A/C just in that area. I just pulled a permit, had a hole cut in the roof and avoided all the codes I could. That A/C runs constantly 24 hrs. a day. I do this mainly to provide a lower temp in the kitchen as not to stress out the 11 compressors and staff we have in there.  Before someone asks, I have tried baking at night. With electric, staff, supervision it was just not cost efficient. I went with the A/C because the landlord picked up half. Lease renewal/img/vbsmilies/smilies/wink.gif

  I had a lot of noise in the beginning. One of my hoods over the deck ovens has a temp. probe in the fan unit itself that would increase fan speed when needed. I had quite a rumbling sound when we kicked on the hood and when the the speed kicked in. It would dissipate after a while. Or maybe  we got used to it?? After looking, we found that the exhaust fan was just placed over the curb on the roof. I was told this was normal. My maintenance guy put some insulation or padding on top of the curb and put the fan back. No noise. We also had a racket which appeared to be in the internal workings. With that, we found that one of the large threaded rods use to support the hood to the drop ceiling was hitting a metal beam. Wrapped. No more noise.
Top Bottom