Weil-McLain 2 Series Manual page 36

®
SlimFit Series 2
DIRECT VENT — Boiler room air openings
Combustion/ventilation air provision
For direct vent installations, combustion air must be ducted directly
from outside to the SlimFit boiler air intake fitting. Two options are
available: sidewall or vertical direct vent. Though combustion air is
ducted to the SlimFit boiler, the boiler room will still require air open-
ings, either for ventilation or for combustion air for other appliances
plus ventilation.
Sizing air openings
Air openings provide for ventilation (as well as combustion air) to
prevent overheating of the boiler controls and boiler space. Air is also
needed for other appliances located in the same space.
Use Figure 32, page 37, selecting the appropriate installation condi-
tions.
Air openings must be sized to handle all appliances
and air movers (exhaust fans, etc.) using the air supply.
The sizing given in Figure 32, page 37 is based on the National Fuel Gas
Code - ANSI Z223.1/NFPA54 – latest edition, allowing adequate air
opening for gravity-vented gas appliances (Category I) when located
in the same space as the SlimFit boiler.
When outside air is ducted as directed in this manual, the SlimFit
boiler is rated as direct vent (pressurized vent), and has varying re-
quirements for combustion and ventilation air, reflected by the special
sizing instructions given in Figure 32, page 37.
The air openings recommended in Figure 32, page 37 will allow ad-
equate ventilation and combustion air provided the boiler room is not
subjected to negative pressure due to exhaust fans or other mechanical
ventilation devices. Refer to the National Fuel Gas Code for dealing
with other conditions.
Louver allowance
The free area of openings means the area
. Be sure to consider this reduction when
installed louvers or grilles
sizing the air openings.
Special considerations
Tight construction
ANSI Z223.1/NFPA54 defines unusually tight construction where:
1. Walls and ceilings exposed to the outside atmosphere have a
continuous water vapor retarder with a rating of 1 perm or less
with openings gasketed, and . . .
2. Weather-stripping has been added on openable windows and
doors, and . . .
3. Caulking or sealants are applied to areas such as joints around
windows and door frames, between sole plates and floors, between
wall-ceiling joints, between wall panels, at penetrations for plumb-
ing, electrical, and gas lines, and in other openings.
For buildings with such construction, provide air openings into the
building from outside, sized per the appropriate case in Figure 32,
page 37 if appliances are to use inside air for combustion and ventila-
tion.
36
COMMERCIAL CONDENSING GAS
after reduction for any
- — Boiler Manual
FIRED WATER BOILER
Exhaust fans and air movers
The appliance space must never be under a negative pressure unless
all appliances are installed as direct vent. Always provide air openings
sized not only to the dimensions required for the firing rate of all ap-
pliances, but also to handle the air movement rate of the exhaust fans
or air movers using air from the building or space.
Motorized air dampers
See "Motorized air dampers" on page 30 for recommendations on
wiring motorized air dampers.
Manifolded combustion air option
1. Multiple SlimFit boilers can use a common combustion air
manifold.
a. Size the duct to provide at least 1 square inch per 1,000 Btuh
total input of connected boilers.
b. Provide minimum clearance to adjacent vents and grade/
snow line as shown in Figure 31.
c. Provide minimum free area in duct (adjusted for louver restric-
tion) of
or divide the total MBH (1000's Btuh) by 2.
d. Example: For an MBS system with total input of 3,000,000
Btuh, or 3,000 MBH: Divide 3,000 by 2 = 1500 square inches
minimum for a combined air duct.
e. If combustion air damper is used, wire to boilers to prevent
operation except after damper has opened (see Motorized
air dampers, above).
Manifolded combustion air option
total boiler input,
Part number 550-100-180/0917