Author Topic: Please help with studying for gas exam, class B  (Read 90 times)

Offline plumberjim40

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Please help with studying for gas exam, class B
« on: January 11, 2021, 10:15:25 PM »
I was wondering if i could get some help with studying for my gas exam.  I am not really understanding the venting and electrical portion of the exam. They never gave us an answer key to our books to see if we are getting it right and now i am trying to figure out how i achieved my answers during my course before writing my exam on jan 25th 21.. some pretty straight fwd some kind of tricky,

Calculate the air requirements from outdoors to a mechanical room equipped with the following appliances.
1)One boiler no draft control 200 KW 
2)one boiler with draft control rated 3000 MBH
3) one duct heater with no draft control rated 75Kw
4) one hot water heater with a draft hood rated at 300,000 Btu/h   
 
answers a)  free area of air supply ______________________mm2
               b) free area of ventilation opening _________________________ mm2   
equipment with draft control
1 sq in per 7000 btu/h up to 1000 MBH plus 1 sq in per 14000 Btu/h for and additional input
no draft control
1 sq in per 30000 btu/h. not really understanding clause 8.4.2 .

I appreciate your help thanks

Jim

Offline Porcupinepuffer

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Re: Please help with studying for gas exam, class B
« Reply #1 on: January 13, 2021, 04:45:08 PM »
 
equipment with draft control
1 sq in per 7000 btu/h up to 1000 MBH plus 1 sq in per 14000 Btu/h for and additional input
no draft control
1 sq in per 30000 btu/h. not really understanding clause 8.4.2 .

I appreciate your help thanks

Jim


Something's a little off with what you have posted here

First: all equipment that will have some form of draft control from 8.4.2:

1 square inch per 7 thousand btu's up to and including 1,000,000 btu's, Once you're dealing with a large enough piece of equipment over 1,000,000 btu's, your size requirements of 1" squared drops to half that at 14,000 btu's instead of 7,000 btu's.

Only under 8.4.3 for a power burner do you then change to 1" squared per 30,000 btu's. I'm not 100% on remembering this, but I believe this would be any type of equipment that doesn't have any draft control device of any form that would require any additional air that gets introducted to the chimney aside from what the burner itself will put into it.

Remember that your ventilation air is totally separate from your combustion air supply requirements and your requirements for the ventilation air are 8.4.1