Was this conversion botched?

Ken C.

A new customer called because his furnace took three to four tries at ignition before the burners would ignite. The furnace had been converted two years ago from oil to (natural) gas-fired, with a Wayne conversion burner and a Honeywell SU 8600 spark ignition. The first thing I noticed was poor combustion, with a yellow flame and an odor of aldehydes. I also noticed the flue still had a barometric damper. I pulled the flue apart and found that the flue collector was choked with soot, so I got the ol' Sootmaster and flue brushes and cleaned the furnace. I also cleaned the spark generator/flame sensor with steel wool. I reassembled the flue and eliminated the barometric damper (checked the chimney, that was clear). I also noticed that there were dual returns, and each return duct had an air intake near the furnace. I've read that this is a no-no, because openings on the returns will suck combustion air away from the burners, so I covered the vents. When I fired the system up again, this time the burner had a blue flame, and ignited on the first try, so I guess I did something right (I'm an experienced plumber, but a newbie at the heating end of the business). The flue had several bends (four 90-degree elbows) to offset the furnace's supply duct, but there wasn't much I could do about that, short of reinstalling the furnace. Should whoever did the conversion from oil to gas have removed the barometric damper? What were the main factors that caused the unit to soot up so bad?

Unknown

What is replacing the Barometric????

If the furnace was equipped with a barometric on oil, it was okay to use a barometric with the gas conversion. It would however have to be a double acting model for gas. If there is not draft control on the unit it can be very dangerous, you need to go back and install one.

You are correct about the returns, you can not take air for combustion and return air from the same space. The return air openings need to be permanently sealed.

I would start from scratch on this unit and make sure the input is correct, find out what the required oil nozzle was and determine gas BTU input by multiplying nozzle size times 138,000 BTU's. If the rating plate is still on the unit that will give you the needed information. Then clock the burner using the 1/2 foot test dial on the meter to determine what your input is.

I would adjust the air for a good blue stable flame that is not roaring or lifting off the burner. You need to do a combustion analysis with a combustion tester. I would also do a test to determine if the heat exchanger is good (that could obviously change the entire picture). Keep in mind that a blue flame does not necessarily mean that combustion is good. You can still be making CO with a blue flame.

I would try to fine someway of eliminating all of those 90 degree elbows.

When you are adjusting the air after determining that input is correct, attach your microamp meter to burner ground (in series)on the S8600 control and adjust your air to get the best microamp reading you can without any fluctuation, 2 to 10 microamps is good, normal is about 3 to 5.

I have an excellent manual available on Conversion Burners and Combustion testing. We also have a class coming up Feb 12 and again March 25 on conversion burners and testing. You have the advantage of an instructor who has installed over 3,000 conversion burners.

Brian_24

You need to check the chimney with a draft gauge and observe what happens when the blower comes on. Sealing the returns off was a good first step however if duct leakage is severe enough it will still back draft your chimney. You also need to check co levels in the vent and stack temperature to really know how well your burner is running, just because it looks good doesn't mean it is. I would have left the barametric on the system and set it up with the draft gauge. I would refer you to www.ncinstitute.com. Jim Davis is awesome when it comes to venting and combustion issues and highly recomend their training.

Ken C.

The furnace had a tee bullheaded off the flue connector. The barometric damper was on one side of the tee. The other side of the tee went into a 90 and then offset around the supply duct. The tee was removed and replaced with a 90, as there was not enough rise to install a vertical draft hood, and not enough clearance from the ductwork to install a horizontal draft hood. Also, the owner had the manual for the conversion burner, it said not to use a damper with a swinging door.
As for eliminating all the elbows on the flue pipe, I don't know of any way other than moving the furnace and ductwork. I think the homeowner may be better off in the long run by replacing the unit with one designed for natural gas.
This combustion tester you mention, is it the same as one used for oil burners? Unfortunately, my boss won't buy one, I would have to buy it myself.

Unknown

Ken if you do not test

you do not know if there is CO present. Tell your boss to give me a call at 401-437-0557 and I will try to educate him on the tremendous liability he is incuring when not testing.

You can by the way use a barometric with conversion burners, they actually work better than a fixed draft hood.

What model Wayne burner is this that does not allow a barometric????

Ken C.

I don't recall the model # of the Wayne burner, but I can get it when I go back to put the barometric damper back. I think I would really benefit from taking your class. Do the classes include any field or lab work on actual units?

Robert O'Connor_7

SOOT?

Three ways I know of 1). Lack of combustion air 2). Blocked flue 3). incorrect gas pressure. YES make sure you check CO, but more inportantly make sure the customer has a CO detector close by. Sometimes another apliance pulls air away from your furnace, ie: Kitchen exhaust, bathroom exhaust, clothes dryer, or a intermittent combination of all three. BOC