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john public · Mar 19, 2008, 08:07 AM

Good Day:

Our furnace is a Heil SP80 model #NU65100BFB2, 100K BTU output, converted to LP gas. The main gas valve failed (Honeywell SV9500M 2682, converted, dead solenoid)

We have just put in a new main gas valve (Honeywell SV9501 M2056), and personally put in the gas conversion from NG to LP. The output pressure on the manifold is exactly 2.5" WC (as reqested in the new literature for LP), confirmed the jets on the manifold as #54 LP orifice. We used a $4000 NIST calibrated Digitron to check the pressure through the enitre heating cycle.

Whats getting me a little concerned is that the flame (nice blue, no yellow, no visible sooting) across the manifold outlet to the heat exchanger is considerably larger than the original valve. The jet is the size of the shell on the HX, and a ribbon of flame is seen across the outlet of the manifold. THere does not seem to be any negative reaction, but the flame characteristics are jsut differnt than before. The unit does not overheat, and seems to cycle properly.

We bought the building with the furnace installed and have no literature. I am not sure if the unit was operating properly when we moved in.

Is there another way to insure that this is the correct set up? Is the 2.5"WC the right value, or will this get adjusted lower for particular instances? I am an oil guy, first time around with a propane unit. Does anybody know where to get an old copy of the installation manuals?

hvac1000 · Mar 19, 2008, 11:29 AM

Make sure the pressure is set to the furnace label and not the gas valve. Propane as well as natural gas can be fired at different pressures so you have to use the design pressure for the unit you are working on. It will be on the furnace label.

john public · Mar 20, 2008, 05:10 AM

Originally Posted by john public

Good Day:

Our furnace is a Heil SP80 model #NU65100BFB2, 100K btu output, converted to LP gas. The main gas valve failed (Honeywell SV9500M 2682, converted, dead solenoid)

We have just put in a new main gas valve (Honeywell SV9501 M2056), and personally put in the gas conversion from NG to LP. The output pressure on the manifold is exactly 2.5" WC (as reqested in the new literature for LP), confirmed the jets on the manifold as #54 LP orifice. We used a $4000 NIST calibrated Digitron to check the pressure through the enitre heating cycle.

Whats getting me a little concerned is that the flame (nice blue, no yellow, no visible sooting) across the manifold outlet to the heat exchanger is considerably larger than the original valve. The jet is the size of the shell on the HX, and a ribbon of flame is seen across the outlet of the manifold. THere does not seem to be any negative reaction, but the flame characteristics are jsut differnt than before. The unit does not overheat, and seems to cycle properly.

We bought the building with the furnace installed and have no literature. I am not sure if the unit was operating properly when we moved in.

Is there another way to insure that this is the correct set up? Is the 2.5"WC the right value, or will this get adjusted lower for particualr instances? I am an oil guy, first time around with a propane unit. Does anybody know where to get an old copy of the installation manuals?

Thanks for the headsup. The plate on the furnace is rated in NG, and has a 3.5 kPA rating. The valve was also rated at 3.5 kPA for NG and 2.5 kPA for LP converted, so I assumed that the furnace was also compatible at 2.5 kPA LP. Bad ssumption?

tsa7man · Mar 20, 2008, 05:16 AM

Your model number is not correct... kindly re-check and post it for us. NOTE: on ICP... heil / tempstar furnaces the LP gas pressure is never 2.5 inches of water... if you run it that low you will soot up the unit!! NOTE: that is why I wonder if you converted the unit correctly ! The conversion kit comes with a low pressure LP safety switch that you install before the gas valve to shut down the unit if it sees LOW LP feed from the tank.. . the ID plate will list the Nat. gas pressure at 3.5 inches of WC... LP is usually 10 inches on the manifold side. Post the correct model number and I check the original specs for the unit...

tsa7man · Mar 20, 2008, 05:38 AM

Your model number must be a NUG5100BFB2 (not a (NU6**) the LP conversion kit did not come with the low pressure safety switch... the # 54 orfices is correct for LP... with a factory install manual spec. of 10 inches of water col. On the manifold side, and a min. LP feed pressure from the LP tank while running of 11 inches of water col...