Lennox G60UHV Series Installation Instructions Manual page 6

j WARNING ACAUTION
In the past, there was no problem in bringing in sufficient out-
door air for combustion. Infiltration provided all the air that
was needed. In today's homes, tight construction practices
make it necessary to bring in air from outside for combus-
tion. Take into account that exhaust fans, appliance vents,
chimneys, and fireplaces force additional air that could be
used for combustion out of the house. Unless outside air is
brought into the house for combustion, negative pressure
(outside pressure is greater than inside pressure) will build
to the point that a downdraft can occur in the furnace vent
pipe or chimney. As a result, combustion gases enter the liv-
ing space creating a potentially dangerous situation.
In the absence of local codes concerning air for combus-
tion and ventilation, use the guidelines and procedures in
this section to install G60UHV(X) furnaces to ensure effi-
cient 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 per-
mission from the National Fuel Gas Code (ANSI-Z223.1).
This reprinted material is not the complete and official posi-
tion of the ANSI on the referenced subject, which is repre-
sented only by the standard in its entirety.
In Canada, refer to the standard CSA B149 installation
codes.
&CAUTION
All gas-fired appliances require air for the combustion pro-
cess. If sufficient combustion air is not available, the fur-
nace or other appliances will operate inefficiently and un-
safely, 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, ex-
haust fans, or clothes dryers are used at the same time as
the furnace, much more air is necessary to ensure proper
combustion and to prevent a downdraft. 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 contami-
nants may include bleaches, adhesives, detergents, sol-
vents and other contaminants which can corrode furnace
components,
The requirements for providing air for combustion and ven-
tilation 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 com-
bined 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 un-
confined, it might be necessary to bring in outdoor air for
combustion if the structure does not provide enough air by
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