Ventilation is not that simple. It requires a coordination of several components. Hoods, exhaust make up air and air conditioning. The proper balance of those units can result in a system that is economical to operate. An un balanced combination of those units will result in an expensive to operate, profit draining ventilation system.
The code requires that all the air taken out of your building through the hood, restroom vents, or any other way, must be returned into your building. That air can be no cooler than 10 degrees less than acceptable room temperature. That requires during winter, If your outside temperatures drop much below 70 degrees that the " make up air" will have to be heated.
Conversely, in summer a “make up air unit” will be bringing in super heated air off your roof. You will have to cool that air with a cooling system built into your make up air unit or compensate for it with larger air conditioners. That is if you want the temperature in your shop to be any where near comfortable.
The above can constitute, an expensive to buy, and very expensive system to operate.
When we install a ventilation system where, a pizza oven is the only equipment requiring a hood, we use a hood that will not need a separate make up air system.
We have a hood that is certified By Equipment Testing Laboratories to operate at a low enough exhaust rate that we can bring enough outside air directly into the hood so as a separate make up air unit is not required. Also an A/C system, adequate for the shop, that does not have to combat incoming hot makeup air in the summer, is all that is required.
A rule of the thumb for a separate make up air unit’s operating costs is $1.50 per CFM per year. An uncertified hood for an oven averaging 4000 CFN exhaust rate can cost about $6000.00 per year to operate.
George Mills
