Help Figure Out Exhaust Hood And Makeup Air Needs?
I am starting to think about the ventilation for my kitchen remodel. I wonder if I can get some ideas and advice, please?
Here is my situation:
- The ranges I am considering are commercial 36-inch or 48-inch ranges, so either 6X or 8X burners of appx 33K BTU/hr each. I like to sear, wok, fry, and expect to generate a good amount of smoke, grease, effluent, etc. Although, I wouldn't be doing smoky stuff on more than a couple burners at a time.
- The range will be placed against a wall and will be free-standing, meaning no cabinetry on either side. If I get a 36-inch range, there may be a narrow (15") steel filler table on the side adjacent to a traffic aisle. If I get a 48-inch range, there may be a stainless steel guard shielding the traffic side of the range.
- The wall will have a non-combustible surface, maybe concrete board with an air gap to the studs (still planning), and that surface will either be tiled or sheathed with stainless steel.
- The other side of the wall is the stairwell down to the basement and side door, so ducting can go out the rear of the hood, through the wall into the stairwell, make a 90-deg turn, and through the exterior wall. Ducting of any reasonable size can fit and I don't mind having it exposed in the stairwell. A blower would fit there too.
- The floor is stone tile. Under the floor is the laundry area of the unfinished basement, and ducting can fit down there as well.
- The ceiling is a little under 9 feet. Above the ceiling is the second floor, so ducting in the ceiling is not a good option, it would be very constrained in size.
My tentative idea for the vent hood is to use a ceiling-mounted hood, about 1 foot wider and deeper than the range, so 4 feet wide by 3 feet deep if I get a 36-inch range. Something vaguely along these lines:
http://www.acitydiscount.com/Used-Restaurant-Kitchen-Grease-Exhaust-4ft-Hood-Stainless-Steel.0.105252.1.1.htm The bottom front edge of the hood needs to have at least 6 ft 5 in headroom, so it would be appx 40 inches higher than the burners, but the bottom rear edge could be lower.
So, here are my specific questions, and I'm sure I'm missing some issues too.
1. How do you calculate the required exhaust CFM? Is there a formula based on total range BTU/hr? How do you factor in the placement and dimensions of the hood?
2. How do you calculate the required makeup air CFM? Since I don't have any information of how leaky my house is (it is an old house, that's all I know), I was going to guessestimate something like makeup CFM >= exhaust CFM less 300 CFM. Does that make sense?
3. Where should the makeup air come in? I've seen some commercial hoods where the makeup air comes in at the front edge of the hood, while the exhaust air is pulled from the back edge. Alternatively, I could bring some or all of the makeup air in through a floor vent located under the range.
4. Do I need to heat the makeup air? It is typically 30-40F in winter here. Then again, I won't be running the range 12 hours a day - I might be searing or woking for 10 minutes, for the rest of the cooking I would turn the blowers down. Do you think that bringing the makeup air in through the hood, or under the hot range, would mitigate any heating needs?
5. I am not so wild about having a giant lump of stainless steel filling the ceiling, so I was thinking about constructing a wooden hood, style consistent with the upper cabinets, and using a steel hood liner in that. What do you think?
6. Has anyone had a custom hood or hood liner built by a local sheet metal shop? Did you find that was better, or cheaper, than buying a hood?
My impression is that, when all is said and done, the venting may end up costing me more than the range.
Thanks for helping. Sorry if this topic is kind of arcane.(My next question will be on fire suppression . . . )