Oil furnace with fuel smell through vents

Gar83

I'm new to forum and hope this is question you can help with. We have an oil furnace that was just serviced by furnace guy and now have fuel smell coming through vents especially in bedroom. According to manual I found online the nozzle for this unit which is the AFUE M5S oil furnace should be .50 80 but service guy put in .50 90 . Could that be problem?

Jamie Hall

There are several possibilities — but changing the nozzle is not really one of them. However, doing that without doing a full combustion test on the furnace is a no-no, and the tech. should have left the combustion test printout with you. Do you have it? Can you send the numbers to us?

The most likely problem is that fuel oil got slopped around when the tech. was working — and not cleaned up.

There are, however, more serious problems — like a cracked heat exchanger.

In the meantime, go and get yourself a CO detector or two — they aren't expensive — and put them up.

EBEBRATT-Ed

What @Jamie Hall mentioned. If there is an oil smell in the basement the that can get sucked into the return ducts and cause a smell upstairs.

If the wrong nozzle is in there and you are getting any puff back due to the burner no being adjusted properly that can come out the burner access port or the barometric damper and get sucked into the return.

the third possibility is the furnace heat exchanger is bad (hope not)

Gar83

Is the barometric damper about 1 inch square at top of burner? That sounds like what we have because getting a little smoke on outside of burner. Just noticed that today. And to answer no test done with any paper received. Thanks

PRR

get yourself a CO detector or two — they aren't expensive — and put them up.

I just got one (my Hawk was getting old). I prefer First Alert to K-brand for reasons.

First Alert CO710

Runs on battery for a decade. Supposed to slip onto two screws but the hole dimensions are poor, I just set it on a shelf. It's not a wake-the-dead peeper like the old Hawk (panicked the dogs) but should work.

EdTheHeaterMan

I can't help but think that this is a Mobil Home furnace with a Concentric Roof Jack. The fact that it is using a .50 nozzle and that the service tech used a 90° spray angle leads me to believe that they have a Nordyne M5S. Broan, Miller, and several other name brands are sold by Nordyne. Although they stopped specifying 90° nozzles over 40 years ago when thy started using flame retention burners like the RW Beckett AF burner. They should put the 80° nozzle in that burner.

That furnace with the concentric venting is not easy to get combustion numbers because of the vent design. There is no access to the inner exhaust vent because it is completely covered by the outer air intake pipe. Another issue is that the blower return air opening is the front door of the furnace. It is the upper section of the door where the louvers and air filter are, the lower solid section of the door covers the burner compartment, and separates it from the room air where the furnace is located. The combustion air comes from the Roof Jack. I don't know of anyone that routinely does combustion analysis because there is no way to do it without drilling a 1/4" hole in the actual heat exchanger then pugging the hole with a 1/4-20 bolt with 500° RTV silicone. ( there are instructions to that effect in the manual). So you would be drilling a hole in the heat exchanger right where the blower compartment exerts the greatest negative pressure on the HX, and that hole you just drilled in it would certainly let odors from combustion into the home.

There are 2 possibilities here. The service Tech spilled a little oil inside the heater while changing the fuel pump strainer, nozzle or oil filter (if located inside the furnace) and did not do a good enough job cleaning up after themselves. That oil odor would smell like you are near the diesel fuel pump at the gas station. A raw fuel smell.

the other possibility is a breach in the HX and that would smell a little different. more like being parked behind a diesel bus at a traffic light, and smelling the exhaust. Two completely different smells. If you have the exhaust odor then you test the heat exchanger for a breach or crack or hole in the HX with smoke bomb or draft gauge measuring the draft over the fire (using the inspection opening) An experienced pro knows how to test the heat exchanger)

Also… the M5S will not have a barometric draft control (damper) on it. That is considered a direct vent appliance where the air for combustion and the exhaust is located in the same outdoor pressure zone. (meaning on the same side of the house… in this case the top side)

In either case, the offending company should take responsibility for the odors and return under a warranty on their workmanship to, at least find the source of the odor. That is what my company would do. But the guys I sold my company to would want to charge you for fixing their mistake. Hope you have a reputable service person.

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1816823#Comment_1816823

No, that's not the barometric damper. That's the inspection port. And you should NEVER see smoke coming from there… or anywhere. Please shut off the emergency switch and get a qualified oil tech to diagnose and repair your furnace before it starts snowing soot in your house.

Gar83

Appreciate the insight all have given repair guy is coming tonight. Thanks Again

Greening

Check the oil tank or piping has not leaked.

Katerina

Thanks for this info — much appreciated! I just had a new Miller installed in my mobile home, and I'm having the same issue with a "diesel exhaust" smell coming through the vents at times, sometimes more than others. And I have a burning question: Are Miller furnaces supposed to have a three-cycle run — first cycle for heating, second cycle everything stops to cool down, third cycle to purge? My previous furnace did this, and there was no smell at all, but this new one only runs one cycle, purging at the end, which is when the diesel smell happens (and sometimes slightly at the beginning of the next cycle, as if it hasn't purged completely).

My previous furnace would run the heat for several minutes, then turn off for a few more, then turn on again for a few more to release residual heat — no smell at all.

My neighbor says his new Miller has the three-cycle function. Aren't they all supposed to have that?

It makes sense that in the cooling / not running cycle, any residual exhaust could drift up the chimney before the final purge. Anybody know? Many thanks!

Katerina

BTW, the company that installed the furnace has been back three times, but can't solve the problem. When I asked about the three cycles, they said it was correctly programmed at the factory. Thanks!

EBEBRATT-Ed

No such thing as 3 cycles.

With the furnace sitting idle the thermostat calls for heat which starts the oil burner

When the furnace temperature gets warm the blower starts and starts blowing warm air through the ducts. The burner continues to run.

When the thermostat is satisfied the burner shuts off and the indoor blower continues to run untill the furnace has cooded down then the fan shuts off. No the furnace sits idel until the thermostat calls for heat again.

That's normal operation. I never heard anyone call it 3 cycles.

SuperTech

Because those furnaces don't have much of a chimney and low draft through them they will have enough heat in the combustion chamber to reactivate the fan and limit control and bring the fan back on after the burner and fan have shut off once already.

Most likely the new furnace doesn't an adjustable fan and limit control. It probably has a couple of cheap bi metal switches instead.

Maybe your installer can try increasing the post purge delay on the oil burner in an attempt to cool the chamber down.