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SlimFit
Series 2
®
DIRECT EXHAUST — Boiler room air openings
(Category IV)
Combustion air provision
The SlimFit Commercial boiler can use inside air if no contami-
nants are present in the boiler space. (If contaminants are likely
to be present, install the boiler as a direct vent appliance, using
the appropriate vent instructions in this manual.)
The boiler room must be fitted with combustion air openings large
enough to provide air for all appliances in the room. Use the fol-
lowing information to size the openings. Ensure the installation
complies with all applicable codes and standards.
Sizing combustion 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 25, page 31, selecting the appropriate installation
conditions.
Air openings must be sized to handle all appliances
and air movers (exhaust fans, etc.) using the air
supply.
The sizing given in Figure 25, page 31 is based on the National
Fuel Gas Code - ANSI Z223.1/NFPA54 – latest edition, allow-
ing adequate air openings for gravity-vented gas appliances
(Category I) in addition to that needed for the SlimFit boiler.
The SlimFit Commercial boiler is rated Category IV (pressurized
vent), and has varying requirements for combustion and ventila-
tion air, reflected by the special sizing instructions given in this
manual.
The air openings recommended in Figure 25, page 31 will allow
adequate 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 - ANSI Z223.1/NFPA54 –
latest edition for dealing with other conditions.
Free area — louver allowance
The free area of openings means the area after reduction for
any installed louvers or grilles. Be sure to consider this reduc-
tion when sizing the air opening.
30
commercial condensing gas
— Boiler Manual
-
fired water boiler
Special considerations
Tight construction
National Fuel Gas Code - ANSI Z223.1/NFPA54 – latest
edition 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 plumbing, 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 25, page 31 if appliances are to use inside
air for combustion and ventilation.
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 appliances, 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
If the air openings are fitted with motorized dampers, electrically
interlock the damper to:
•
Prevent the boiler from firing if the damper is not fully open.
•
Shut the boiler down should the damper close during boiler
operation.
The SlimFit control provides a Closure switch function which will
prevent the boiler from firing if the damper is not fully open or
closes during boiler operation. Please refer to the Boiler Manual
for installation and wiring instructions.
Part number 550-100-561/0224
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