Laars LT Series, Installation And Operation Instruction Manual

Page 14

Table 2.  Required Combustion Air Pipe Material.

SECTION 4.   Installation   

(continued)

4.3  Combustion Air

LT Series water heaters must have provisions for 

combustion and ventilation air in accordance with the 

applicable requirements for Combustion Air Supply 

and Ventilation in the National Fuel Gas Code, 

ANSI Z223 1; or in Canada, the Natural Gas and 

Propane Installation Code, CSA B149.1. All applicable 

provisions of local building codes must also be 

adhered to.

An LT Series unit can take combustion air 

from the space in which it is installed, or the 

combustion air can be ducted directly to the unit. 

Ventilation air must be provided in either case.

4.3.1  Combustion Air from Room

In the United States, the most common requirements 

specify that the space shall communicate with the 

outdoors in accordance with method 1 or 2, which 

follow. Where ducts are used, they shall be of the 

same cross-sectional area as the free area of the 

openings to which they connect.

Method 1

: 

Two permanent openings, one 

commencing within 12" (300mm) of the top and one 

commencing within 12" (300mm) of the bottom, of 

the enclosure shall be provided. The openings shall 

communicate directly, or by ducts, with the outdoors 

or spaces that freely communicate with the outdoors. 

When directly communicating with the outdoors, or 

when communicating to the outdoors through vertical 

ducts, each opening shall have a minimum free area 

of 1 square inch per 4000 Btu/hr (550 square mm/kW) 

of total input rating of all equipment in the enclosure. 

When communicating to the outdoors through 

horizontal ducts, each opening shall have a minimum 

free area of not less than 1 square inch per 2000 Btu/

hr (1100 square mm/kW) of total input rating of all 

equipment in the enclosure.

Method 2

: 

One permanent opening, commencing 

within 12" (300mm) of the top of the enclosure, shall 

be permitted. The opening shall directly communicate 

with the outdoors or shall communicate through a 

vertical or horizontal duct to the outdoors or spaces 

that directly communicate with the outdoors and shall 

have a minimum free area of 1 square inch per 3000 

Btu/hr (734 square mm/kW) of the total input rating of 

all equipment located in the enclosure. This opening 

must not be less than the sum of the areas of all vent 

connectors in the confined space.
Other methods of introducing combustion and 

ventilation air are acceptable, providing they conform 

to the requirements in the applicable codes listed 

above.
In Canada, consult local building and safety codes or, 

in absence of such requirements, follow CAN/CGA 

B149.

4.3.2  Ducted Combustion Air

The combustion air can be taken through the wall, or 

through the roof.  When taken from the wall, it must 

be taken from out-of-doors by means of the horizontal 

wall terminal. When taken from the roof, a field-

supplied rain cap or an elbow arrangement must be 

used to prevent entry of rain water.
As allowed by local codes use ABS, PVC, CPVC, 

Polypropylene for the Combustion air intake.  Route 

the intake to the water heater as directly as possible. 

Seal all joints. Provide adequate hangers. The unit 

must not support the weight of the combustion air 

intake pipe. Maximum linear pipe length allowed is 

shown in Table 6. 
Subtract 5 allowable linear ft. (1.5m) for every elbow 

used.
The connection for the intake air pipe is at the top of 

the unit.
In addition to air needed for combustion, air shall also 

be supplied for ventilation, including air required for 

comfort and proper working conditions for personnel.

 COMBUSTION AIR INSTALLATION STANDARDS

MATERIAL

UNITED STATES

CANADA

ABS

ANSI/ASTM D1527

Air pipe material must be chosen CPVC, sch 40, ANSI/ASTM, 

Polypropylene 

based upon the intended application of the 

water heater.

PVC, sch 40 Polypropylene

ANSI/ASTM D1785/1738 or D2665

CPVC, sch 40 Polypropylene

ANSI/ASTM F441

 UL1738, ULC S636.

Single wall galv. steel

26 gauge