Weil-McLain 550 MBH Nstallation And Operation Manual page 29

®
SlimFit Series 3
DIRECT EXHAUST — Boiler room air openings
Combustion air provision
The SlimFit Commercial boiler can use inside air if no contaminants 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, see Figure 12, page 22)
The boiler room must be fitted with combustion air openings large enough
to provide air for all appliances in the room. Use the following 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 16, page 30, 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 16, page 30 is based on the National Fuel Gas
Code, ANSI Z223.1, allowing 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 ventilation air, reflected
by the special sizing instructions given in this manual.
The air openings recommended in Figure 16, page 30 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 for dealing with other conditions.
Free area — louver allowance
The free area of openings means the area
. Be sure to consider this reduction when sizing the air
louvers or grilles
openings.
Part number 550-100-168/0516
COMMERCIAL CONDENSING GAS
after reduction for any installed
—
-
FIRED WATER BOILER
Special considerations
Tight construction
ANSI Z223.1 defines unusually tight construction
where:
1. Walls and ceilings exposed to the outside atmo-
sphere 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 16, page 30 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 dur-
ing boiler operation.
To accomplish this interlock, wire an
(proving the damper open) in series with the thermo-
stat input to the boiler. The boiler will not start if this
contact is open, and will shut down should it open
during operation.
Boiler Manual
isolated contact
29