Why Divide Gas BTU Rating By 30 To Get CFM

[ScrewyBrewer]

I've been reading where John Blichmann wrote an article for BYO Magazine in November 2009 on how to calculate the CFM needed to correctly vent both gas and electric powered indoor brewing systems.

For electric heating elements he divides the wattage by 17.6 and the answer is the number of CFMs needed to exhaust off boil vapors and aromas. So a 5,500 watt electric heating element divided by 17.6 will require 312 CFM to vent off the brewing vapors.

For gas burners he divides the BTU rating by 30 and the answer is the number of CFMs needed to exhaust off boil vapors and aromas. But an 80,000 BTU gas burner divided by 30 will require 2,666 CFM to vent off the brewing vapors, carbon monoxide and enough fresh air to work in safety and comfort.

I've been trying to find out just how John came up with the 17.6 and 30 numbers to plug into his electric and gas CFM calculation. Any help will b appreciated.

[mtsoxfan]

Vince, glad to see you back.
The scienctists will give a more detailed answer, but the electric has no by product to vent off as does gas.

[John Sand]

The real question is why would anyone want to vent out brewing aromas? Oh yeah, wait. I remember: I'm married!

[Brewbirds]

Hopefully Da'Yooper will chimes in on your thread Screwy he has posted some good info on this in the past.

Happy belated Turkey day to you and your family and glad to see you on the I hope that this post means you are getting settled into the new digs and are ready to ramp up the brewing.


I will be interested to see how this thread develops because for my current glass top stove brewing I have not had worried about venting but we want to move and I am trying to decide if Natural Gas availability should be something to consider and I saw you asking about venting a while ago.

[BigPapaG]

Vince, I'm not sure how he comes up with those numbers either...

But I do know that one must consider the number of BTU's, the area of the room (available combustion air) and any static pressure contained within the ductwork used for venting...

A good example is the technique used to calculate the required CFM moved by a range hood in a kitchen...

Perhaps the following will help?

http://www.todayshomeowner.com/how-to-c ... -fan-size/

And

http://www.vent4less.com/78.html?m9:pos ... easy-steps

And here is how to calculate the amount of combustion air required for a given BTU rating...

http://www.comfort-calc.net/Combustion_ ... ation.html

[ScrewyBrewer]

Happy belated Turkey Day to you all too. We're finally moving into our apartment and hope be completely moved in a few weeks from now, so brewing again is getting closer and closer. Still plenty of running around to do and last minute things to deal with but thank you for posting that information I will be reading it and asking more questions.

The brewroom I'm planning is still months and months away, the house is still no more than a vacant lot now. But I'm fully invested in electric brewing indoors in part of the garage. Sizing the a to remove gas fumes and boil vapors needs about 12 times the cfm rating needed to remove only the boil vapors from an electric kettle. Natural gas was not an option in the new brewroom but I'm looking forward to electric brewing and posting again as I learn more about it.