Designer Guide

12
LOCHINVAR, LLC
300 MADDOX SIMPSON PKWY
LEBANON, TN 37090
www.lochinvar.com
Designer’s Guide / Knight XL Boiler
Chapter 2 – Combustion and
Ventilation Air
Everybody’s gotta breathe. Even boilers need air. Air seems easy enough. You stand in the
equipment room and you breathe comfortably. Open a door. Open a window. This is a big
room. There’s lots of air in here for the boiler. Right?
The average person inhales 400 to 500 cubic feet of air in a 24 hour period. A 500,000 Btu/hr
boiler will draw 113.19 cubic feet of air every MINUTE! A 20 by 20 by 8 foot equipment room
holds 3200 cubic feet of air. That’s a volume of air to last you or me over six days. A 500,000
Btu/hr Knight XL will consume 6400 cubic feet of air in 28 minutes.
Therefore, a good, easy flow of fresh air is 100% necessary for clean, efficient combustion. With
the Knight XL boiler, we expect the two pipe system illustrated in Chapter 1 will be the most
popular design used in the field. However, the last two offerings in the venting chapter allowed
for the combustion air to be drawn from the equipment room.
This chapter explains the methods to ventilate the equipment room to meet the combustion
requirements of the Knight XL. This chapter lists several techniques to size the air openings that
will deliver room air. If there are other appliances in the room requiring air, their air requirements
must be including when sizing the air openings.
Provisions for combustion and ventilation air must be
designed and installed in accordance with “Air for
Combustion and Ventilation”, of the latest edition of the
National Fuel Gas Code, ANSI Z223.1, (in Canada, the
latest edition of CGA Standard B149 Installation Code for
Gas Burning Appliances and Equipment) or applicable
provisions of the local building codes.
NEGATIVE PRESSURE IN THE EQUIPMENT ROOM
It is important to NEVER have a negative pressure on the equipment room. Exhaust fans are
popular in equipment rooms to exchange the air. If the exhaust fan pulls air OUT, then a negative
pressure occurs in the room. Therefore, the combustion and ventilation air openings must be
sized to supply all the equipment PLUS the air for the exhaust fan.
COMBUSTION AND VENTILATION AIR SIZING CALCULATIONS
The sizing calculations in this section are based on “Free Area”. The louvers or grill used on the
air openings must have a net free area equal to or greater than the value derived in the
calculations. The Free Area in a louver or grill is defined as the open, unblocked area. Louvers,
grills, mesh, blades, all will block a given amount of space in the louver’s overall dimension.
Consult the louver manufacturer for exact net free area of the louver.
Air