MG2S Installation Manual

20
High Altitude Application
High altitude conversion with this furnace depends on
the installation altitude and the heating value of the gas.
Installation of this furnace at altitudes above 2,000 feet
shall be in accordance with local codes, or in the absence
of local codes, the National Fuel Gas Code, ANSI Z223.1/
NFPA 54 or National Standard of Canada, Natural Gas &
Propane Installation Code CGA B149.1. Please consult
your local code authority.
The installer must indicate the furnace has been
converted to high altitude. This may be accomplished
by marking the rating plate with a permanent marker.
WARNING:
The reduction of input rating necessary for high
altitude installation may only be accomplished
with factory supplied orifices. Do not attempt to
drill out orifices in the field. Improperly drilled
orifices may cause fire, explosion, carbon
monoxide poisoning, personal injury or death.
The furnaces are shipped from the factory with orifices
and gas regulator settings for natural gas operation at sea
level altitudes. At 2000 feet, the NFGC requires that this
appliance be derated 4% for each 1000 feet of altitude.
For example, the input needs to be reduced 8% at 2,000
feet, 12% at 3,000 feet, etc. This deration is in reference
to the input rate and gas heating value at sea level.
To derate the furnace requires knowing the heating value of
the gas at the installation site. Heating values at particular
job sites vary for two reasons:
1. The chemical mixture of the gas varies across regions
and is expressed as the sea level heating value.
2. The heating value varies by altitude. For this reason,
especially in high altitude areas, the local gas utility
specifies the heating value at the residence’s gas meter
as the local value.
For added flexibility, two tables have been provided for
natural gas installations with high or low heating values
at sea level. Table 13 & Table 14, (page 36) contain
the manifold pressure and orifice sizes to use at various
altitudes. Table 13 (HIGH) is for natural gas installations
with a heating value of more than 1,000 Btu per cubic foot
and Table 14 (LOW) is for less than 1,000 Btu per cubic
foot. To determine which table to use:
1. Consult the local utility for the local heating value at
your installation site.
2. From Table 12, (page 36), find your local heating
value as supplied by the utility company. Follow down
the column and stop at your altitude level.
3. If your sea level heating value is HIGH, use Table 13
or if it’s LOW, use Table 14. See example above.
EXAMPLE
Elevation: .................................................. 5,000 feet
Type of Gas: ........................................... Natural Gas
Local Heating Value of Gas: .............................. 750
From Table 11, find 750 and follow down the column,
stop at the 5,000 feet row. The heating value listed is
LOW. Table 14 will be used to determine orifice size
and manifold pressure.
After changing the orifices, it is required that you measure
the gas input rate. This may be accomplished in the usual
way, by clocking the gas meter and using the local gas
heating value. See Verifying & Adjusting the Input Rate
section on page 23.
IMPORTANT NOTE:
Observe the action of the burners to make sure there
is no yellowing, lifting or flashback of the flame.
Converting to LP/Propane Gas at Altitudes
between 0 & 10,000 FT.
Converting two-stage furnaces to LP/Propane requires
the replacement of the burner orifices and converting the
regulator to LP. All furnace models need to be derated
when converted to LP. See Table 11, (page 36).
WARNING:
The furnace was shipped from the factory
equipped to operate on natural gas. Conversion
to LP / Propane gas must be performed by
qualified service personnel using a factory
supplied conversion kit. Failure to use the proper
conversion kit can cause fire, explosion, property
damage, carbon monoxide poisoning, personal
injury, or death.
WARNING:
Shut off the gas supply at the manual gas shutoff
valve, before disconnecting the electrical power.
A fire or explosion may result causing property
damage, personal injury or loss of life. Failure to
follow the safety warnings exactly could result in
serious injury, death or property damage.
WARNING:
To avoid electric shock, personal injury, or death,
turn off the electric power at the disconnect or the
main service panel before making any electrical
connections.