Hi cmshaner
Welcome to the HVAC Group!
Congratulations on achieving a 90% on your exam! Proper ventilation is extremely important and some codes require combustion air from outdoors, especially for confined spaces. A confined space is defined as a room containing less than 50 cubic feet of volume for every 1000 BTU per hour of appliance input.
However if a small mechanical room is connected to adjacent spaces through large air passages like floor-joist spaces, the room may not need additional combustion air despite indoor sheeted walls and a door separating the mechanical room from other indoor spaces. On the other hand, if the home is usually airtight, even a large mechanical room may be unable to provide adequate combustion air.
A sealed combustion heating system is always preferable for reliable combustion air delivery and combustion gas venting. Passive intake vents from outdoors or neighboring indoor areas are too easily converted from air supplies by wind, exhaust fans, or other chimney.
The location of a passive combustion air inlet is important. The wind creates a positive pressure area on the buildings windward side and a negative pressure near walls parallel to the wind direction. If the inlet were located in a negative pressure area, this inlet could suck air out of the building instead of letting air in.
When the combustion air duct brings outdoor air into a living area, a control mechanism, like a damper may be necessary to prevent residents from closing the duct permanently because of the drafts it causes. Isolating the central heater in an airtight room and providing this room with outdoor combustion air is preferred over dumping combustion air into living spaces.
It is very important that the nozzle match the manufactuers specifacations. There are many different designs of nozzles and it must match that particular burner design. Using a nozzle that does not match that burner design could result in incomplete combustion. Nozzle spray angles will vary for different combustion chambers and range from 30-70 degrees and 70-90 degrees.
Good Luck with your studies!