ICP N9MSE0401410A, Service And Technical Support Manual

SERVICE AND TECHNICAL SUPPORT MANUAL

Gas Furnace: N9MSE

Specifications  subject to change without notice.

440 04 4401 03

5

Figure 2

Orifice Hole

A93059

BURNER

ORIFICE

For proper operation and long term reliability the furnace input

rate must be /

−

2  percent of input rate on furnace rating

plate, or as adjusted for altitude.
The gas input rate on rating plate is for installation at altitudes

up to 2000 ft. (610 M).

NOTICE

The NATURAL GAS manifold pressure adjustments in 

Table 3

compensate for BOTH altitude AND gas heating value. DO

NOT apply an additional de

−

rate factor to the pressures shown

in 

Table 3

. The values in this Table and NOT referenced to sea

level; they are AS

−

MEASURED AT ALTITUDE.

The heating content of natural gas at altitude may already

provide for a reduction in capacity or altitude. Refer to 

Table 3

.

No adjustments to the furnace may be necessary at altitude for

certain gas heating values.
Refer to the instructions provided in the factory-specified

LP/Propane conversion kit for instructions for setting gas

manifold pressures for LP/Propane applications.

In the USA, the input rating for altitudes above 2000 ft. (610 M)

must be reduced by 2 percent for each 1000 ft. (305 M) above

sea level refer to 

Table 1

. The natural gas manifold pressures

in 

Table 3

 adjust for BOTH altitude and natural gas heating

value.
In Canada, the input rating must be reduced by 5 percent for

altitudes of 2000 ft. to 4500 ft. (610 to 1372 M) above sea level.

The natural gas manifold pressures in 

Table 3

 adjust for BOTH

altitude and natural gas heating value.

NOTE

:  For Canadian altitudes of 2000 to 4500 ft. (610 to 1372

M), use USA altitudes of 2001 to 3000 ft. (611 to 914 M) in

Table 3

.

To adjust manifold pressure to obtain the proper input rate, first,

determine if the furnace has the correct orifice installed. At

higher altitudes or different gas heat contents, it may be

necessary to change the factory orifice to a different orifice.

Tables have been provided in the furnace Service and

Technical Manual to match the required orifice to the manifold

pressure to the heat content and specific gravity of the gas. To

do this:

1. Obtain average yearly gas heat value (at installed

altitude) from local gas supplier.

2. Obtain average yearly gas specific gravity from local gas

supplier.

3. Find installation altitude range for your installation in the

manifold pressure tables in 

Table 3

.

4. Find closest natural gas heat value and specific gravity in

Table 3

. Follow heat value and specific gravity lines to

point of intersection to find orifice size and low-and

high-heat manifold pressure settings for proper

operation.

5. Check and verify burner orifice size in furnace. NEVER

ASSUME ORIFICE SIZE. ALWAYS CHECK AND

VERIFY.

NOTICE

If orifice hole appears damaged or it is suspected to have been

redrilled, check orifice hole with a numbered drill bit of correct

size. Never redrill an orifice. A burr

−

free and squarely aligned

orifice hole is essential for proper flame characteristics.

6. Replace orifice with correct size, if required by 

Table 3

.

Use only factory

−

supplied orifices. See EXAMPLE 1.

EXAMPLE 1:

0 - 2000 ft. (0 - 609.6M) altitude

Heating value = 1050 Btu/cu ft.

Specific gravity = 0.62

Therefore: Orifice No. 44

(Furnace is shipped with No. 44 orifices. In this example, all

main burner orifices are the correct size and do not need to be

changed to obtain proper input rate.)

Manifold pressure: 3.4-in. w.c. (847 Pa).

NOTE

:  To convert gas manifold Table pressures to Pascals,

multiply the in.w.c. value by 249.1 Pa/in. w.c. (1 in. wc. = 249.1
Pa).

Table 1

Altitude Derate Multiplier for USA

ALTITUDE

FT. (M)

PERCENT

OF DERATE

DERATE MULTIPLIER

FACTOR*

0–2000

(0

−

610)

0

1.00

2001–3000

(610

−

914)

4

−

6

0.95

3001–4000

(914

−

1219)

6

−

8

0.93

4001–5000

(1219

−

1524)

8

−

10

0.91

5001–6000

(1524

−

1829)

10

−

12

0.89

6001–7000

(1829

−

2134)

12

−

14

0.87

7001–8000

(2134

−

2438)

14

−

16

0.85

8001–9000

(2438

−

2743)

16

−

18

0.83

9001–10,000

(2743

−

3048)

18

−

20

0.81

* Derate multiplier factors are based on midpoint altitude for altitude range.

NOTE

:  

For Canadian altitudes of 2000 to 4500 ft. (610 to

1372 M), use USA altitudes of 2001 to 3000 ft. (610 to 914
M)

Check Inlet Gas Pressure

The inlet gas pressure must be checked with the furnace

operating in maximum heat. This is necessary to make sure the

inlet gas pressure does not fall below the minimum pressure of

4.5 in. w.c.

1. Make sure the gas supply is turned off to the furnace and

at the electric switch on the gas valve.

2. Remove the 1/8 in. NPT plug from the inlet pressure tap

on the gas valve.

3. Connect a manometer to the inlet pressure tap on gas

valve.

4. Turn on furnace power supply.