Exhaust smell when running furnace

[Berniezee]

We bought a used 2008 Montana 3465SA last summer, 2016. For the past three weeks we've been running the furnace nearly every night because it gets into the mid 40's here. I smell exhaust some nights and in the middle of the night, on two separate nights, the carbon monoxide detector in the bedroom went off. What is the likely cause of this problem and what should I do about it?

To get through the night safely we ventilated the RV by opening the bedroom window and turning on the bathroom exhaust fan, after turning off the furnace, then we sleep in the cold. The first night the CO alarm went off we changed the batteries. Both nights the CO alarm went off we stopped the beeping by removing the middle battery while we were ventilating. Because I smelled car exhaust both nights that the CO alarm went off I believe my CO alarm is working properly. This occurred between 3:00AM and 5:00 AM when there are no camp fires burning or nearby vehicles running outside. I did add an aluminum window screen over my furnace exhaust as recommended by the campground host to prevent burning or hot particles from exiting the furnace to avoid starting a forest fire because it was very dry and there was a high risk of forest fires. This window screen is black with soot. We've been camping at an elevation of 6,000 to 7,500 feet above sea level.

I need a permanent fix to this problem. Any advice would be greatly appreciated. Thank you in advance.

[WeBeFulltime]

I would IMMEDIATELY take that window screen off the exhaust as that is likely your problem! Camp hosts aren't always qualified to give "advice" of this nature.

[mjammersc]

In addition to taking the screen off, take a flashlight and look around into the furnace and burner to ensure nothing (wasps, etc) has decided to nest inside of it or left and debris from failed attempts.

[CORattler]

If your CO alarm is alarming, do not use the furnace until the issue is resolved. Purchase a ceramic electric space heater to ward off the chill. Safety is paramount!

[kdeiss]

Originally Posted by mjammersc

In addition to taking the screen off, take a flashlight and look around into the furnace and burner to ensure nothing (wasps, etc) has decided to nest inside of it or left and debris from failed attempts.

X2 I once found a dead mouse in their also mud dobber nest around the squirrel cage fan!

[BB_TX]

I also would take that screen off. Propane does not have any solids to produce "burning particles". It could also be restricting the furnace exhaust flow and causing it to go places it shouldn't. In any event, it should not be used until the problem is found and resolved. Too much at stake to take the chance. A couple of electric heaters in the meantime.

[Berniezee]

Thanks for the advice! This morning my wife noticed that the screen was completely covered with ash thus obstructing the exhaust. Something must have been inside and burned. The screen is gone and I looked into the furnace area and found nothing unusual so I hope the problem is solved.

[h2ojocky]

Under no circumstance would I disable a carbon monoxide detector, especially if you smell something abnormal. Carbon monoxide is odorless and breathing it can be fatal!

[Berniezee]

Please don't misunderstand. The CO detector was NOT disabled. It was simply turned off during the ventilation time. Immediately after ventilation was finished, the CO detector battery was reinstalled and the CO detector was tested, found to be working properly, and it was hung back on the wall, where it was originally located. After ventilation the CO detector was "on" and was not beeping because the room air was clean, i.e. No more CO inside the RV.

I did a few simple things to the furnace that hopefully solved the problem and The furnace will be tested/run with nobody in the rv to see if the CO detector alarms. We are taking this situation very seriously and we plan on using an electric heater until the furnace is tested. Thanks again for all of your advice!!!

If anyone has advice on how to test the furnace I would like to hear it.

[mjammersc]

The one other item I would look into when you are checking your system is if there may be recommendations from the manufacturer of the furnace for high altitude operation. Your altitude and the soot being generated triggered something I had seen before somewhere. I did a quick google search and that is one of the signs of poor fuel air mix at altitude on LP appliances. Worth checking into.

[CORattler]

Originally Posted by mjammersc

The one other item I would look into when you are checking your system is if there may be recommendations from the manufacturer of the furnace for high altitude operation. Your altitude and the soot being generated triggered something I had seen before somewhere. I did a quick google search and that is one of the signs of poor fuel air mix at altitude on LP appliances. Worth checking into.

Good thoughts. Altitude also plays a part in gasoline powered generators. The manual for my Honda EU2000i talks about this.
From the manual:
Carburetor Modification for High Altitude Operation
At high altitude, the standard carburetor air-fuel mixture will be too
rich. Performance will decrease, and fuel consumption will increase. A
very rich mixture will also foul the spark plug and cause hard starting.
Operation at an altitude that differs from that at which this engine was
certified, for extended periods of time, may increase emissions.
High altitude performance can be improved by specific modifications
to the carburetor. If you always operate your generator at altitudes
above 5,000 feet (1,500 meters), have your authorized Honda servicing
dealer perform this carburetor modification. This engine, when
operated at high altitude with the carburetor modifications for high
altitude use, will meet each emission standard throughout its useful
life.
Even with carburetor modification, engine horsepower will decrease
about 3.5% for each 1,000-foot (300-meter) increase in altitude. The
effect of altitude on horsepower will be greater than this if no
carburetor modification is made.
When the carburetor has been modified for high altitude operation,
the air/fuel mixture will be too lean for low altitude use. Operation at
altitudes below 5,000 feet (1,500 meters) with a modified carburetor
may cause the engine to overheat and result in serious engine damage.
For use at low altitudes, have your servicing dealer return the
carburetor to original factory specifications.