Sooty furnace

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Old 03-12-08, 09:28 AM
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Question Sooty furnace

Have a "Williams" brand propane wall furnace that soots up. Took it apart and rinsed about a quart of soot out of the flu and heat exchanger. Measured 10 WC" on the control valve, the plate says I should have 10.5 WC". The tank reads 11WC". Why am I getting this soot problem? Any ideas out there?

-UD
 
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Old 03-12-08, 01:16 PM
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Originally Posted by utility dodge View Post
Have a "Williams" brand propane wall furnace that soots up. Took it apart and rinsed about a quart of soot out of the flu and heat exchanger. Measured 10 WC" on the control valve, the plate says I should have 10.5 WC". The tank reads 11WC". Why am I getting this soot problem? Any ideas out there?

-UD
Don't you get soot from an improper air/fuel mixture?
 
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Old 03-12-08, 01:20 PM
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watch out...
soot = incomplete combustion = carbon monoxide

Is this furnace installed in a small mechanical room that perhaps has little or no access to sufficient amounts of air for safe combustion?

The gas pressure you are readin gis normal. That is not the reason for the soot.
 
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Old 03-12-08, 02:34 PM
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How are the flames? Blue or Yellow?

Any other gas appliances on this tank?

How big is the tank?

Where are you out of?
 
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Old 03-12-08, 04:20 PM
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Originally Posted by Jay11J View Post
How are the flames? Blue or Yellow? (Flame is blue)

Any other gas appliances on this tank? (NO)


How big is the tank? (250 GAL)

Where are you out of?
(NORTH OF YOSEMITE IN SONORA, CALIFORNIA)

Check after few days there was no soot present but a light ash was visible when I tapped on the heat exchanger.

Thank for your help. U. D.
 
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Old 03-12-08, 04:24 PM
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Originally Posted by pflor View Post
watch out...
soot = incomplete combustion = carbon monoxide

Is this furnace installed in a small mechanical room that perhaps has little or no access to sufficient amounts of air for safe combustion?

The gas pressure you are readin gis normal. That is not the reason for the soot.
This furnace is located in kitchen/dining area and has plenty of air circulation. The propane supply had 80% in the tank. I don't know why it sooted up like that. There was a light ash a few days later.
U.D.
 
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Old 03-13-08, 03:14 AM
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This unit is in a closet in the kitchen/dining area I suppose...pls confirm. There may be enough air for your family to breath and for the burning of the stove flames when cooking...but furnaces need a tremendous amount of fresh air.

As an example, with natural gas appliances, 15 cubic feet (CF) of air are needed to burn 1 cubic foot (CF) of nat-gas (so a furnace with an input of 100,000 BTUH will burn 100CF of gas in that hour and will need 100CF of fresh air every hour). With propane you need at the very least twice as much (2.5 times to be precise). Please provide the dimensions (length, width & height) of the mechanical room where the furnace is enclosed.

Don't assume that b/c is inside the house you have plenty of air circulation.

I would strongly suggest that someone performs for you a CO test of the combustion gases inside the smoke pipe (the furnace's vent pipe)

If it is not the lack of sufficient amounts of combustion-air (and this almost surely is your problem), then the burners are in need of some serioius fine-tuning, they are likely not mixing sufficient amounts of PRIMARY AIR with the gas that is being admitted by the burner orifices...the air-shutters may be obstructed or in need of calibration.
 
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Old 03-13-08, 01:21 PM
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Soot build-up in furnace.

Originally Posted by pflor View Post
This unit is in a closet in the kitchen/dining area I suppose...pls confirm. There may be enough air for your family to breath and for the burning of the stove flames when cooking...but furnaces need a tremendous amount of fresh air.

As an example, with natural gas appliances, 15 cubic feet (CF) of air are needed to burn 1 cubic foot (CF) of nat-gas (so a furnace with an input of 100,000 BTUH will burn 100CF of gas in that hour and will need 100CF of fresh air every hour). With propane you need at the very least twice as much (2.5 times to be precise). Please provide the dimensions (length, width & height) of the mechanical room where the furnace is enclosed.

Don't assume that b/c is inside the house you have plenty of air circulation.

I would strongly suggest that someone performs for you a CO test of the combustion gases inside the smoke pipe (the furnace's vent pipe)

If it is not the lack of sufficient amounts of combustion-air (and this almost surely is your problem), then the burners are in need of some serioius fine-tuning, they are likely not mixing sufficient amounts of PRIMARY AIR with the gas that is being admitted by the burner orifices...the air-shutters may be obstructed or in need of calibration.
MORE INFO:
This unit was not professionally installed. It is wall mounted in a room that is approximately 10ftx15ftx7ft. There is nothing in front of the unit obstructing air flow. There was a plume of soot along the ceiling above the furnace. There is no air mixture adjustment on the burner manifold. We're keeping an eye on the fixture so we don't have another build-up of soot. I would just like to get a handle on the possible causes of the problem. It is a Williams brand residential wall furnace model # 3509621. Thanks for your input I appreciate it.

U.D.
PS: cook stove and water heater are both electric.
 

Last edited by utility dodge; 03-13-08 at 01:27 PM. Reason: add ceiling height.
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Old 03-13-08, 01:45 PM
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Please know that by code, and, most importantly, for safety reasons, a gas burning appliance should have available a minimum of 50 cubic feet of room volume per 1,000 Btuh of appliance's input.

Your room, reportedly is 10x15x7. That adds up to 1,050 cubic feet, so the largest size furnace that could safely operate in this space should have an input no greater than 21,000Btuh. Else, a source of direct outside air should be made available to help with the combustion air requirements of the appliance.

And if this area is well protected from drafts (good windows, good weatherstripping, etc) even the 50 cf per 1MBH would be insufficient.

what's the input of your wall furnace?
 

Last edited by pflor; 03-13-08 at 03:09 PM.
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Old 03-13-08, 06:28 PM
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The williams Furnace you have is classified by the manufacturer as a Monterrey, Top Vent, Propane-fired wall furnace it has an input rating of 35,000 Btuh. Not enough air is the reason for the soot.

For the size of the living space where this wall furnace is installed, you should not have anything with an input larger than 21,000Btuh

http://67.114.233.34/CGI-BIN/LANSAWE...50BB2M+PRD+ENG

Consider yourself lucky that a tragedy has not occurred there yet.
 
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Old 03-14-08, 09:42 AM
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Question furnace soot

Thanks for the BTU info. I work on an Indian Reservation for a Housing Authority Entity and this furnace is in an older cabin that was remodeled 2 years ago. What is our best option to remedy this situation? Should the unit be replaced, Should we add additional ventilation from outside, or...? Please advise. Thanks again. U.D.

Originally Posted by pflor View Post
The williams Furnace you have is classified by the manufacturer as a Monterrey, Top Vent, Propane-fired wall furnace it has an input rating of 35,000 Btuh. Not enough air is the reason for the soot.

For the size of the living space where this wall furnace is installed, you should not have anything with an input larger than 21,000Btuh

http://67.114.233.34/CGI-BIN/LANSAWE...50BB2M+PRD+ENG

Consider yourself lucky that a tragedy has not occurred there yet.
 
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Old 03-14-08, 11:59 AM
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I wanted to just add something. If the real cause was a lack of fresh air, shouldn't the flame at least start out burning full and blue, but then as time goes along, progressively get yellower and or weaker?, f0o fresh air intake was the real cause (which it could be, don't get me wrong. I'm just saying...)

I wonder how air tight that cabin is? When I hear the word cabin, I think of some hunting lodge that leaks like a sieve.

Could he tell something by opening a window and seeing if the flame turns to blue?
 
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Old 03-14-08, 01:07 PM
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I encountered once a case, in the house of a former neighbor, in which a nat. gas furnace & water heater (120MBH total combined input) had been enclosed in a room, part of a basement that had been finished (insulation, vapor barrier, sheet rock, carpet...the whole nine yards). They had even cut a 2-ft x 2-ft louvered opening in one of the walls of this improvised mechanical/hiding room, so the furnace would be able to "breath" taking air from the rest of the basement.

Dusting-off the unit, the owner one day accidentally pushed the manual-ON button of the fan-limit switch. Not knowing what to do to turn the fan OFF, she called the gas co., and the tech that came, upon removing he service door, immediately condemned it. Cracked heat exchanger!!!, I was told he had said after seeing some serious soot build up by the burners.

I brought my Digital Monoxor (CO tester), which has a scale 0-2,000 ppm.
EPA recommends exposures not higher than 35ppm over an 8-hr period
An 800ppm exposure kills within 45 minutes
I drilled a small hole in the smoke pipe, fired-up the unit and let it run for a few minutes, put the tester's probe inside and the readings, in a mater of seconds, went off the scale.

There was no cracked heat exchanger and no CO readings inside the house, but sure enough the availability of combustion air in that basement was meager, and we're talking a full size basement 30ft x 20ft x 7ft (a much larger area than this cabin). I sized a duct with a small inline fan that would run with the furnace blower, adjusted the RPM's to get the CFMs needed for the total input of both appliances, and that took care of business.

But, no, in retrospect, regrettably it did not occur to me to look at the color of the flame, or if it would progressively be changing from blue to yellow as you suggest, which by the way is what would be expected to happen...but that could take some time, you know?
 
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Old 03-14-08, 01:20 PM
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Utility Dodge - furnace advice

Since this seems to be a single room cabin, I would not recommend a direct air intake (the room could get cold). You may as well open a window...which is not good either (again, the room would get cold)

Have someone run a heating load calculation, well done, so you know for sure how many Btu's are needed, and buy yourself a direct-vent furnace. They take air for combustion directly from the outside and vent the combustion gases to the outdoors as well. You can't go wrong with that.
 
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Old 03-14-08, 02:01 PM
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Question Sooty furnace

Originally Posted by pflor View Post
Since this seems to be a single room cabin, I would not recommend a direct air intake (the room could get cold). You may as well open a window...which is not good either (again, the room would get cold)

Have someone run a heating load calculation, well done, so you know for sure how many Btu's are needed, and buy yourself a direct-vent furnace. They take air for combustion directly from the outside and vent the combustion gases to the outdoors as well. You can't go wrong with that.
I went back to the cabin to take an accurate measurement of interior living space. It is actually 3 rooms with total volume of 3,626 cu ft. not including the bathroom which has the only door aside from the entry door. The rest of the cabin is open to all rooms. The place is 30 or 40+ years old and has some newer windows and new exterior door. Is there a chart available for figuring out the proper appliance BTU input for volume of living space? When I divide 3,626 x 50 = 72.52 does that mean I need BTU input of 72,000? Can you give me the right formula I'm rusty when it comes to math. Thanks, U.D.
 
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Old 03-14-08, 02:23 PM
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Wink

Lot of ifs ifs here Id say. Is this a older unit?? Is the burner ok?? the venturi in it OK?? Line size to unit right . When you check the W/C for 11" do you have all the other gas burners on in the home. Is the unit set for the altitude there??? Orifice ok and for LP. Have you checked the flue pipe ?? Is it clear. No down draft??? Do you have a fireplace in the home that can pull back down the flue???
 
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Old 03-14-08, 02:56 PM
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We have found many Williams furnaces sooted. These were nat gas (we don't work on LP). We found the reason was the orifice did not line up with the venturi, which made the gas deflect off the wall of the venturi slowing down the velocity and hence producing a lazy luminous flame which would impinge on the heat exchanger producing soot.
these were almost always on models with a horizontal venturi and orifice. We found we could actually bend the orifice straight and all was well. Well most of the time. In the absence of this repair we would leave the wall furnace capped off and recommend repairs. I would recommend if this is the problem to purchase a new burner assembly.
Hope this is helpful.
 

Last edited by mbk3; 03-14-08 at 03:19 PM.
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Old 03-14-08, 06:54 PM
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Originally Posted by utility dodge View Post
I went back to the cabin to take an accurate measurement of interior living space. It is actually 3 rooms with total volume of 3,626 cu ft. not including the bathroom which has the only door aside from the entry door. The rest of the cabin is open to all rooms. The place is 30 or 40+ years old and has some newer windows and new exterior door. Is there a chart available for figuring out the proper appliance BTU input for volume of living space? When I divide 3,626 x 50 = 72.52 does that mean I need BTU input of 72,000? Can you give me the right formula I'm rusty when it comes to math. Thanks, U.D.
Your math is right. The new volume that you're now reporting changes the picture. For the total available space you are reporting, you DO have sufficient air there for good combustion. I'd suggest that you follow mbk3's recomendation which is an excellent one.

The soot thereby is not due to lack of air. Back then to my suggestion on posting #7 that fine-tuning seems to be needed
 
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Old 03-14-08, 07:27 PM
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I might also add, the only way to properly clean a Williams burner is to use water. Inside the burner (on most models I believe) there is a horizontal plate with holes. It seems to collect dust very easily and typically blowing air thru only partially cleans. And being located in a kitchen means alotof foot traffic. The more traffic the more dust is stirred up. Couple with a smooth floor the dust will be pulled into the burner venturi.
 
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