Every year, when I turn my natural gas furnace on for the first time, there’s a smell that persists for about one week. The best description I can make is a burning metal/chemical smell. I maintain the furnace myself by removing the burners, cleaning them out with a rifle-cleaning wire brush, vacuum everything out, and check the shape/color of the flames, adjusting the air entrainment as needed. This is done before every heating season. The humidifier is also thoroughly cleaned and a new water pad installed. While there’s some surface rust in the burner cavities, there are no perforations. There’s no smell from the AC, just the heat. Our CO monitor never registers above zero.
Any ideas?
Replies
Many furnaces produce a "burning" smell which is dust which has settled on the outside of the heat exchanger being burned off at the beginning of the heating season.
>>I maintain the furnace myself . . . and check the shape/color of the flames, adjusting the air entrainment as needed.
Do you mean adjusting the primary air shutters on the burners?
With the development of reasonably priced CO meters and combustion analyzers in the last 15 years or so, we have learned that you can not
properly adjust a furnace by visual appearance of the flame - it is not necessarily true that " a blue flame is a clean flame."
It is easy to close down a shutter and shoot the CO levels very high without affecting the color or shape of the flame. (See attached photo*)
Are you checking the draft in the flue? Measuring the temp of the flue gases? Measuring the temp rise of the circulated air? Inspecting the flue and the chimney? How does you draft hood look?
How is your A/C coil? My experience is that when there is significant dust burning off the heat exchanger, there is also excessive dust and crud on the coils, sometimes restricting air flow and causing short cycling.
At least it sounds like you have a decent, digital readout CO detector. Where do you have it installed?
I've attached a photo with a couple of screen shots from a little AVI I did during one CO Safety Analysis, measuring CO in the top of the heat exchanger. The top pic shows the very high levels with the shutter almost closed, the bottom shows significantly lower levels with the shutter open. Although it is not obvious in the pics, the flame shapes and colors did not change with the changes in the shutter openings.
(At the levels in the top pic, I would have had to disable the furnace, even without flue gas or CO spillage into the house air.)
God never gives us small ideas.
Sojourners: Christians for Justice and Peace
Thanks, Bob. Forgive my incorrect terminology; I adjust the small rotating valve at the front end of each burner, although I've only slightly adjusted one. As per a local HVAC contractor, I look for a mostly bluish, correctly-shaped flame. I've not closely inspected the flue or any temps. The AC coil is spotless, although it does get vacuumed at least yearly with everything else. Our CO meter is on the first floor, with the furnace (13 years old) in the basement. The blower motor was replaced 02/2004.
>>I adjust the small rotating valve at the front end of each burner, although I've only slightly adjusted one. As per a local HVAC contractor, I look for a mostly bluish, correctly-shaped flame.
With natural gas, that valve should be fully open.
As I said, we have learned in the last few years that the color of the flame is essentially meaningless for determining combustion efficiency or co production.
And, unfortunately, there are a lot of HVAC guys who have not kept up with the times.
Even without a past history of CO in the house, it is still vital to be sure your gas appliances are not producing excess CO - you never know when the vent might get screwed up.
For example, an underfired burner can produce huge amounts of CO and the resulting low flue temp lead to corrosion in the flue and/or chimney, which in turn can lead to failure of the flue and/or chimney and that CO getting into the home.
THE BPI and NCI CO Safety Analysis protocols call for disabling any gas appliance producing more than 400 ppm regardless of how ell the vents are working.
God never gives us small ideas.
Sojourners: Christians for Justice and Peace
Edited 10/7/2004 11:40 am ET by Bob Walker
Bob, how often do you change the co sensor? :)
(Smilies would come in handy sometimes)
The CO monitors I use in my house call for replace evey 5 years, but if they got hit by some huge dose (like rightnext to a car exhaust) I'd replace them then.
My CO meters get calibrated every 6 months; I've replaced the sensor in the Monoxor II once - I blew it before UI knew it was a bad idea to test it at the car's tail pipe!
God never gives us small ideas.
Sojourners: Christians for Justice and Peace
Perfectly normal.
Really? My neighbors don't seem to get this smell.
They get the smell. It may vary a bit based on whether you ran the AC during the summer, and of course some people's smellers are more sensitive than others.
FYI - My wood stove does the same thing first time I fire it up (like today!) I agree that it may be dust or just the paint drying out again after absorbing a bit of humidity...
yep, even elec baseboard heat gives the "old sock" smell.
only thing immune is likely HPs, as the temp is too low to 'fragrant" the dust
Over,
I have lived in three houses with forced hot air heat over the last 31 years. Two were gas and one oil, all of them did the same thing on initial startup each year. There is always some dust and other residue on the outside of the heat exchanger that you will never remove with a normal cleaning. The first time the furnace is fired up, this "dirt" burns off and that is what you are smelling. Sort of like the first time you put a brand new cast iron skillet on the stove. Same thing happens when you start a brand new engine after installing it in a car ... all the residue from storage and handling burns off the exhaust and it can stink for a while. After a few minutes of running it goes away.
It has nothing to do with the actual fuel burning in the furnace.
Nothing to worry about. I bet your neighbors get the same thing, they are just used to it and don't notice.
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
Edited 10/6/2004 10:34 pm ET by MrBill