Hi,
Was approached by the owner of a Subway franchise who wants to vent the excess heat (and aroma believe it or not) from above the bread oven and convection oven. There is a well vented attic above.
He wanted me to install passive louvers, but I think an exaust fan with a damper controlled by a manual switch or thermoswitch would be better.
A couple questions:
1. Any guesses on a cfm rating?
2. Any guess on a sones/noise rating?
3. Any problem venting directly into the well-vented attic, or should I install a roof damper?
Thanks, Jon
Replies
Being as this is a commercial space, you have to follow local bldg and health dept rules for what you are proposing.
I would not vent to attic.
Fire suppression of the hood would probably be a basic requirement. At the least, fire rating separations cannot be compromised.
A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
1. Any guesses on a cfm rating?
You would size the hood to extend over the appliance 6" on each exposed side. Based on the size of the hood, 200 cfm/linear foot or 50 cfm/square ft.
2. Any guess on a sones/noise rating?
Can be from 5 sones to 30 sones, deping on how the fan is selected.
3. Any problem venting directly into the well-vented attic, or should I install a roof damper?
Lots of problems venting into the attic. The question raises issues of experience, knowledge and code familiarity. Do the background and find out what the local code /health department requires. If the owner insists on doing the wrong thing, or you don't know any better, walk away.
A good, professional installation would include a suitable hood, exhaust fan, back draft damper, insulated roof curb, galvanized steel or aluminum exhaust duct and some basic controls.
Since this isn't a required fan, and it isn't above an actual cook surface, you might have more flexibility than with a range-top fan, depending on your local AHJ.
Basically, it should be possible for someone with the right tables and numbers on the surface temp of the oven to compute how much convective updraft there is. You need a CFM to better that. It's shouldn't be absolutely necessary to have a hood over the unit, provided you have sufficient CFM and the layout is suitable. OTOH, with a properly arranged hood you could do without the fan, simply relying on convection.
Whether required by code or not (and fan or not), it's prudent to install a fire shutter. And never vent into an attic, especially since you'll be venting warm moist air that will cause condensation once it gets up there.
happy?