I.C.E. MTI 11-300 - Manual (Page 6)

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1. Air from inside the building – Opening of 1 square inch (sq. n.) per 1000
Btuh of input, but never less than 100 sq. in.
2. Air from outside (ducted) – Opening of 1 sq. in. per 2000 Btuh
3. Air from outside (direct opening) – Opening of 1 sq. in. per 4000 Btuh
VENTING
All duct furnaces must be vented outside of the heated space. All venting installations shall
be in accordance with the latest editions of ANSI Z223.1 The National Fuel Gas Codes, part
7, Venting of Equipment, or applicable provisions of local codes and ordinances.
The duct furnace must be connected to a factory built chimney or vent complying with a
recognized standard or a masonry or concrete chimney lined with a lining material
acceptable to the authority having jurisdiction.
The duct furnace will be classified in accordance with ANSI standards as follows:
o Category 1 – Non- condensing appliance with negative vent pressure
o Category 111 – Non-condensing appliance with positive vent pressure
VERTICALLY VENTED FURNACE – Category 1 (see figure 1 in appendix C)
1. Use single wall or double wall (type B) vent pipe of diameters listed in the following
table for the appropriate models:
2. Maximize the height of the vertical run of vent pipe. A minimum of five (5) feet
(1.5m) of vertical pipe is required. The top of the vent must extend at least two (2)
feet (0.61m) above highest point on the roof. (Use Listed Type B vent for external
runs). A weatherproof vent cap must be installed to the vent termination.
3. Horizontal runs must not exceed 75% of the vertical height of the vent pipe, up to a
maximum of ten (10) feet (3m). Horizontal runs should be pitched upward ¼” per
foot (21 mm) and should be supported at 3 foot (1m) maximum intervals.
4. Design vent pipe to minimize the use of elbows. Each 90 is equivalent to 5 feet
(1.5m) of straight vent pipe run.
5. Vent pipe should not be run through unheated spaces. If such runs cannot be
avoided, insulate vent pipe to prevent condensation inside vent pipe. Insulation
should be a minimum of ½” (12.7mm) thick foil faced fibreglass, minimum 1 ½#
density.
6. Dampers must not be used in vent piping runs. Spillage of flue gases into the
occupied space could result.
7. Vent connectors serving Category 1 heaters must be connected into any portions of a
mechanical draft system operating under positive pressure.
HORIZONTALLY VENTED FURNACES – Category 111(see figure 2 in appendix C)
Pressures in Category 111 venting systems are positive and therefore care must be taken to
avoid flue products form entering the heated space. Use only vent material and components
that are UL listed and approved for Category 111 venting systems.
WARNING: Do not use Type B vent within a building on horizontally vented units.