10
5-572.10
Equation 10.1 - Manifold Pressure for Gas Heating
Values Different Than Shown in Table 10.1
Table 10.3 - High Altitude Kit Contents
Table 10.2 - High Altitude Kit Selection Table
jkl
j
Applies to both installations in the U.S. and Canada.
k
Applies to both natural and propane gas.
l
Sizes 75-400 require a kit qty. of 1, sizes 500-800 require a kit qty of 2,
sizes 840-960 require a kit qty of 3.
j
Values shown are for 3.5" W.C. manifold pressure for Natural Gas and 10.0"
W.C. for Propane Gas. If the local utility supplies gas with a different Btu/ft³
value, use Equation 10.1 to calculate the required manifold pressure.
k
Gas heating values shown are derated 4% per 1,000' of elevation (10%
between 2,000' and 4,500' elevation in Canada) in accordance with ANSI
Z223.1 and CSA-B149, respectively.
l
945 Btu/ft³ for Canada
m
2,250 Btu/ft³ for Canada
n
When installed at altitudes above 2,000', a pressure switch may need to be
changed. Refer to Tables 10.2 and 10.3 to determine if a switch change is
required.
Considerations for Elevation
The standard ratings for the duct furnace(s) used in these units
are certified for elevations up to 2000 feet above sea level.
Operation at elevations above 2,000 feet requires ratings be
reduced 4% for each 1000 feet above sea level per ANSI
Z223.1. The exception is for units in Canada, CSA requires that
ratings be reduced 10% for elevations between 2,001 and 4500
feet. The following instructions are for units that will be installed
over 2,000 feet elevation. If this does not apply, you may skip
ahead to the Electrical Connections section on page 11.
Manifold Pressure Adjustment
The unit manifold pressure is factory set for operation at
elevations up to 2000 feet as follows:
• For
Natural Gas
units, 3.5" W.C. based on a gas heating value
of 1,050 BTU/ft³.
• For
Propane Gas
units, 10.0" W.C. based on a gas heating
value of 2,500 BTU/ft³.
For higher elevations, some utility companies may derate the
BTU content (heating value) of the gas provided at altitude to a
lower value to allow certain heating appliances to be used with
no manifold pressure adjustments. For this reason it is necessary
that the supplying utility be contacted for detailed information
about the gas type and BTU content (heating value) before
operating any heater. Table 10.1 shows the standard derated
heating values of natural and propane gases at various
elevations.
NOTE:
For units equipped with two-stage or modulating gas
controls, only the high fire manifold pressure needs to be
adjusted. No adjustments to the low fire manifold pressure are
necessary on these units.
Selection of the Proper High Altitude Kit
All units installed at elevations greater than 2000 feet above sea
level require a kit, in addition to potential manifold pressure
adjustment outlined in the previous step. To determine the proper
kit to use, refer to Table 10.2.
Table 10.3 shows the contents of the kit. For more information,
refer to the latest revision of Modine Bulletin 75-530.
If the utility is supplying gas with heating values
SAME
as shown
in Table 10.1, the manifold pressure should remain set to 3.5"
W.C. for natural gas and 10.0" W.C. for propane gas and you
may proceed to the section on this page titled “Selection of the
Proper High Altitude Kit”.
If the utility is supplying gas with heating values
DIFFERENT
than shown in Table 10.1, use Equation 10.1 to determine the
appropriate manifold pressure for the elevation and gas heating
value being supplied. Note what that value is, as it will be
needed later for Start-Up. Proceed to the section on this page
titled “Selection of the Proper High Altitude Kit”.
If a unit is to be installed at higher elevations AND converted from
natural gas to propane gas operation, a propane conversion kit
must be used in conjunction with the manifold pressure
adjustment and high altitude kit listed above. For the Selection
and Installation Instructions for propane conversion kits, please
see the latest revision of Modine Bulletin 75-511.
Table 10.1
Gas Heating Values at Altitude (Btu/ft
³
)
jkln
Altitude (ft)
Natural Gas
Propane
0-2,000
1,050
2,500
2,001-3,000
929
l
2,212
m
3,001-4,000
892
l
2,123
m
4,001-4,500
874
l
2,080
m
4,501-5,000
856
2,038
5,001-6,000
822
1,957
6,001-7,000
789
1,879
7,001-8,000
757
1,803
8,001-9,000
727
1,731
9,001-10,000
698
1,662
Where:
MPELEV = Manifold Pressure (" W.C.) at installed
elevation
BTUTBL = BTU/ft³ content of gas from Table 10.1
BTUACT = BTU/ft³ content of gas obtained from the
utility company
MPSL = Manifold Pressure (" W.C.), at Sea Level
(use 3.5" W.C. for natural gas and
10.0" W.C. for propane)
INSTALLATION
Model Model
Size
Elevation Above Sea Level (ft)
2,001-5,500 5,501-6,500 6,501-7,500
All
All
Item Code
67248
67248
67248
Item
Code
Kit Contents
High Altitude
Conversion Label
Pressure
Switch
Installation
Instructions
67248
Yes
No
Yes
