Airease 95G2DFE, Installation Instructions Manual

507206-01

Page 7  of  59

Issue 1337

All  gas-fired  appliances  require  air  for  the  combustion 

process.  If sufficient combustion air is not available, the 

furnace  or  other  appliance  will  operate  inefficiently  and 

unsafely.  Enough air must be provided to meet the needs of 

all fuel-burning appliances and appliances such as exhaust 

fans which force air out of the house.  When fireplaces, 

exhaust fans, or clothes dryers are used at the same time 

as the furnace, much more air is required to ensure proper 

combustion and to prevent a down draft.  Insufficient air 

causes incomplete combustion which can result in carbon 

monoxide.

In addition to providing combustion air, fresh outdoor air 

dilutes contaminants in the indoor air.  These contaminants 

may include bleaches, adhesives, detergents, solvents and 

other contaminants which can corrode furnace components.

The requirements for providing air for combustion and 

ventilation depend largely on whether the furnace is installed 

in an unconfined or a confined space.

Unconfined Space

An unconfined space is an area such as a basement or large 

equipment room with a volume greater than 50 cubic feet 

(1.42 m³) per 1,000 Btu (.29 kW) per hour of the combined 

input rating of all appliances installed in that space.  This 

space also includes adjacent rooms which are not separated 

by a door.  Though an area may appear to be unconfined, 

it might be necessary to bring in outdoor air for combustion 

if the structure does not provide enough air by 

Do not install the furnace in a corrosive or contaminated 

atmosphere.  Meet all combustion and ventilation air 

requirements, as well as all local codes.

 CAUTION

air is brought into the house for combustion, negative 

pressure (outside pressure is greater than inside pressure) 

will build to the point that a down draft can occur in the 

furnace vent pipe or chimney.  As a result, combustion 

gases enter the living space creating a potentially dangerous 

situation.

In the absence of local codes concerning air for combustion 

and ventilation, use the guidelines and procedures in this 

section to install these furnaces to ensure efficient and safe 

operation.  You must consider combustion air needs and 

requirements for exhaust vents and gas piping.  A portion 

of this information has been reprinted with permission from 

the National Fuel Gas Code (ANSI-Z223.1/NFPA 54).  This 

reprinted material is not the complete and official position 

of  ANSI on the referenced subject, which is represented 

only by the standard in its entirely.

In Canada, refer to the CSA B149 Installation codes.

infiltration.  If the furnace is located in a building of tight 

construction with weather stripping and caulking around 

the windows  and doors, follow the procedures in the “Air 

from Outside” section.

Confined Space

A confined space is an area with a volume less than 50 

cubic feet (1.42 m³) per 1,000 Btu (.29 kW) per hour of 

the combined input rating of all appliances installed in that 

space.   This  definition  includes  furnace  closets  or  small 

equipment rooms.

When the furnace is installed so that supply ducts carry 

air circulated by the furnace to areas outside the space 

containing the furnace, the return air 

must be

 handled by 

ducts which are sealed to the furnace casing and which 

terminate outside the space containing the furnace.  This 

is especially important when the furnace is mounted on 

a platform in a confined space such as a closet or small 

equipment room.  Even a small leak around the base of the 

unit at the platform or at the return air duct connection can 

cause a potentially dangerous negative pressure condition.  

Air for combustion and ventilation can be brought into the 

confined  space  either  from  inside  the  building  or  from 

outside.

Air from Inside

If  the  confined  space  that  houses  the  furnace  adjoins  a 

space categorized as unconfined, air can be brought in by 

providing two permanent openings between the two spaces.  

Each opening must have a minimum free area of 1 square 

inch (645 mm²) per 1,000 Btu (.29 kW) per hour of total 

input rating of all gas-fired equipment in the confined space.  

Each opening must be at least 100 square inches (64516 

mm²).  One opening shall be within 12 inches (305 mm) of 

the top of the enclosure and one opening within 12 inches 

(305 mm) of the bottom.  See Figure 4.

Figure 4

Equipment in Confined Space - All Air from Inside