LAARS Mighty Therm HH-PH (Sizes 175-400) - Installation, Operation and Maintenance Instructions - Manual (Page 7)

Mighty Therm HH-PH Hydronic Boilers Page 7
NOTE: Check with louver manufacturers for net
free area of louvers. If not available, add 50 percent
for each screen/louver to the net free area. Check all
local codes applicable to combustion air.
2D-1. Outdoor Air Supply
When combustion air comes directly through an
outside wall, each opening must have a minimum free
area of at least one square inch for each 4,000 BTU/h
input of the total input rating of all appliances in the
enclosed area. (In Canada, refer to CGA B149.1
and .2.)
2D-2. Indoor Air Supply
Confined and non-confined areas have different
requirements for installation. Consult the latest edition
of the National Gas Code for installation requirements.
2D-3. Exhaust Fans or Vents
Any equipment which uses air or removes air
from the boiler room can use up the combustion air
supply or reverse the natural draft action of the
venting system. This could cause flue products to
build up in the boiler room. More air must be supplied
to make up for the decrease. This must be designed by
a qualified engineer.
2E. Venting of Combustion Products
2E-1. General Information
When installed indoors, the drafthood and the
vent damper device (models 175 and 250) must be
connected to a venting system without alteration. The
venting system must be installed by a qualified
installer and in accordance with the latest edition of
ANSI Z223.1. In Canada, the installation must be in
accordance with CAN1-B149.1 or .2, and any local
codes that apply.
The vent pipe must have a listed vent cap and
extend at least 2 feet (0.6 m) above any object within a
10 foot (3.0 m) radius (see Figure 15).
Figure 14. Typical Roof Mounting.
Required Net Free Opening Area
Directly from Outside
At Top At Bottom
Model in. 2 cm 2 in. 2 cm 2
175 44 284 44 284
250 63 406 63 406
325 82 529 82 529
400 100 645 100 645
Note: For screens or louvers, add 50%.
Table 2. Air Openings to Outside.
Figure 15. Indoor Installation Venting.
Notes:
1.
The drafthood must sit directly on top of the boiler
as shown and must not be altered in any manner.
2. An Underwriters' Laboratories listed vent cap is
required to eliminate downdraft and allow the
boiler to function properly.
3. Use approved roof fitting.
4. Vent damper is required on models 175 and 250.
2D. Combustion and Ventilation
Air Supply
All indoor installations must have openings to
outside air for combustion, ventilation and dilution of
flue gases from inside the building (see Figure 15 and
Table 2). Laars does not recommend indoor
installations that do not provide combustion air from
outside the building.
Boiler rooms which are confined spaces require
two permanent air supply openings: one within
12 inches (305 mm) of the ceiling, the other within 12
inches (305 mm) of the floor.