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Remember that you are working on a heating system and not just a furnace. A majority of furnace problems lie outside of the
product itself. Therefore, when trouble-shooting a furnace problem, always check the following items before testing or
replacing components.
#1 - GAS PRESSURE
The gas pressure should be set at a minimum of 11˝ W.C.
with a minimum of 50% and ideally 100% of the gas fired
appliances operating. You should test this pressure with a U-
tube Manometer only. If you choose to use a dial-type
manometer, calibrate it often with a U-tube manometer.
#2 - VOLTAGE
Voltage to the furnace should be between 10.5 and 13.5 VDC
during operation with the interior lights ON and OFF. This
check should be made with the battery, converter or
generator when applicable. Use a digital or analog multi-
meter when taking voltage readings. Do not use a test light. It
does not provide enough useful information for proper
diagnosis.
A furnace is a consumer's friend when the outside
temperature gets colder. Unfortunately though, cold is an
enemy of LP gas. The BTU capacity of LP per volume
decreases as the outside temperature gets colder. Therefore,
based on how full the LP tanks are, the ambient temperature
outside and how many BTU's the furnace is, there may not be
enough gas to sustain ignition on the furnace.
Using the charts below, let's say that a 40,000 BTU furnace
won't fire up, and we also know that the 65 lb. LP bottle on
the RV is 40% full and it is 0 degrees F. outside. One's first
thought might be that the burner or valve is bad. However, if
20 lb. Bottle
65 lb. Under Mtd. LP Gas Tank BTU available at
(*30 lb. bottle multiply X 1.40)
% Full
+20°
60%
36,000
50%
32,400
40%
28,800
30%
25,200
20%
21,600
10%
16,200
% Full
+20°
60%
95,600
50%
86,000
40%
77,000
30%
68,000
20%
58,000
10%
43,200
#3 - DUCTING
Always make sure that the furnace has at least the minimum
number of ducts (not including closeable outlets) called out
in the installation instructions. Check for proper duct
connections at the furnace and heat registers, collapsed
ducts and holes in the ducting. The duct runs must be as
straight and tight as possible. The heat ducts must also be
clean and clear of obstructions.
#4 - RETURN AIR
The return air passage should meet the minimum square
inches as specified for the particular model of furnace in the
installation instructions. This air passage should also be
clean and clear of obstructions. Do not put air filters in this
passage way. Also make sure that combustibles are not
stored in the furnace compartment.
we use the chart, the vaporization capacity of the tank in
these conditions is only 38,500 BTU's. The furnace is not
going to perform very well because there is insufficient BTU
capacity in the tank.
If you were to put an insulated fire resistant blanket over the
tanks and a 75 watt light bulb under that, you would probably
raise the temperature of the bottles 10-20 degrees and
almost double the BTU capacity of the tank. This in turn
would allow the furnace to operate properly. So keep in mind
that a furnace problem is not always a component problem.
0°
-5°
18,000
12,750
16,200
12,150
14,400
11,400
12,600
10,450
10,800
8,100
8,100
6,075
0°
-5°
47,800
36,000
43,000
32,250
38,500
29,250
34,000
25,500
29,000
21,750
21,600
16,200
26
The 4 Always
#1 - Gas Pressure
-10°
-15°
8,500
4,250
8,100
4,050
7,600
3,800
7,300
3,150
5,400
2,700
4,050
2,025
-10°
-15°
23,900
12,100
21,500
11,750
19,250
9,625
17,000
8,500
14,500
7,250
10,800
5,400
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