Makeup Air Unit Required?

[nuuvox000]

Hey everyone, I'm trying to figure out if I need to provide a makeup air unit. The situation is as follows: There is a warehouse that will house a 10,000,000 BTUh oven and it exhausts 12,000 CFM in flue gases with fans to the outdoors. The warehouse and ovens meet the requirements in the IFGC for indoor combustion air. It looks like makeup air is only required if it "interferes with the operation of appliances." Is this the case? I just want to make sure that I'm not missing something that says it's required. I know the IMC requires makeup air for commercial kitchen exhaust systems but this isn't a kitchen. Thanks in advance!

 

[GT-EGR]

Sounds like you’ve read the code and combustion air rules and determined it isn’t legally required - but a makeup air unit is still a good idea. 12,000 CFM is a lot of air to suck in through whatever cracks your building has. But to answer your question, code does permit not having a makeup air unit - but in my experience I only follows this with small heaters.

If that is 12,000 CFM of hot gas, the number could be considerably less CFM when it’s coming into the building at normal temperatures, depends how hot your oven runs.

A makeup air unit is recommended because it lets you control where the air will come into the space, and allows you to filter it and even condition it. If you don’t put one then it’s unfiltered hot/cold air coming in whenever you’ve got the most envelope deficiency, and those locations will be hot/cold spots and get dirty over time.

 

[nuuvox000]

Thank you, that was a very helpful response! You reminded me that this oven is for baking cookies so I'll definitely include a makeup air unit so that we can filter the air coming into the building.

 

[ProcessHVAC]

Check your combustion calcs, you might only need to make up 1/3 or 1/4 of flue gas flow.

 

[nuuvox000]

Will do, thanks for the tip.

 

[chicopee]

12000 cfm of flue gas consists of a certain amount of make up air and a certain amount of fuel. So the amount of combustion will be less than the 12000cfm. You'll need to do a stoichiometry of the fuel to determine the amount of make up air. in the stoichiometry don't forget to include excess air. The operator's manual provided by the manufacturer should have sections about the amount of make up air.

 

[nuuvox000]

Thanks, I did do the stoichiometry calculation and it was only about 3000 CFM. The rest of it is exhausted to remove moisture from their product apparently. Thanks!

 

[nglty]

On a side note
10,000 MBH, even at 90% efficient at all times, you have 1000 MBH of heat loss through the exhaust stack
There are good opportunities to recover a lot of heat from the stack (think boiler stack economizer) to preheat the make-up air.