Stinky Furnace

[Martin Lehman]

I just fired up my gas fired furnace last night and it freekin smells terrible!

I have lived in my home since July of this year and have never use the FAU before (only the A/C). 1100sqft condo built in 1980. FAU is an older Trane model

I visually checked out the furnace and everything looks good(flame, filter, flue pipe, comb. air), being that the unit is around 25yrs old.

Anyway, what is the reason for this terrible smell?

It smells like the ducts are filthy and all the dust and dirt are burning off.??? Well I ran the furnace for about 45 min and the smell did not get any better, so I had to turn off the furnace.

QUESTION: What the heck do you think this is?

Are the ducts just really dirty inside and need to be cleaned? Do I need new ducts? Or is it something else?

My wife is pregnant and due in a couple weeks. We are really going to need heat and air quality that is acceptable in our home.

Thanks

[Les]

Sounds like abnormally long burn-off. Check your filter, fan cage and speed. Slow running blower or clogged filter will cause the exchanger to overheat and burn stuff that has been on there for years. Did you take a carbon monoxide reading?

Usually dirty ducts don't smell for a period of time; only thing you have introduced into the question is heat and that is located at only one place: exchanger.

[Martin Lehman]

Thanks for the fast reply Les,

I did not think to check the fan speed although I do get a sufficent flow of air through the registers.

I have been plannig to replace the filter, but it is not really too dirty.

Can I adjust the speed of the blower motor? I dont have the manu. for this FAU.

No, I have not taken a CO test yet. I dont have a CO tester, better pick one up with that new filter.

[Scottpat]

What is an FAU?

[Bain]

Forced Air ?Unit?.

A twenty-five year old furnace is past its normal economic life. You may have combustion gases entering the house due to a cracked heat exchanger. It would be prudent to slide the blower out so you can take a close look at the heat exchanger, especially with a kid on the way.

John

[Les]

John, good point!

I would get a service person out and be there when they were (to check their work).

I was not clear about the fan speed; sometimes the fan runs slower for a variety of reasons and yes that unit has at least two speeds.

Now my Grandfather advice: Don't screw around with it!

[hausdok]

Hi,

John makes a good point, you might have a cracked heat exchanger. Or, it might be something else - like a dead bird or rodent that's fallen into the vent and become wedged between sections of the chamber.

Yesterday, I put in a call to Ellis Prach, the Heat Exchanger Expert, because I'd had an interesting situation the day before with a Lennox G-12. He called me back last night and we had a fascinating discussion about heat exchanger longevity.

He makes a pretty good case for why we inspectors should consider at least sliding out blower cages to do a penetration test. After that talk, I'm not sure that I'm ever going to trust my visual on a furnace again. If you've got sufficient technical skills to do it without damaging your furnace, slide out that blower and take a look, Martin. It can't hurt.

ONE TEAM - ONE FIGHT!!!

Mike

[Martin Lehman]

Forced air unit (fau)

I sure hope it's not the Heat exchanger...............$$$$$$....................[:-weepn]

Thanks guys

[randynavarro]

Yes, I would also go with the dead rat, mouse or bird theory.

[Martin Lehman]

I'm going to have San Diego Gas & Electric inspect the furnace, test for gas leaks and for CO in my home and go from there.

Dead animal in the vent pipe huh.....looks like I'm going on the roof tonight!

The vent is a straight shot from the furnace through the roof, except for one 45 degree bend just after the vent connector.

[Brandon Chew]

The rodent or its nest could also be on the air distribution side of the heat exchanger. I hope it's not anything more than debris, somewhere, in the system.

[Terence McCann]

It's pretty good odds that the heat exchanger is shot. Don't waste anytime having it checked out and in the meantime I wouldn't use it.

[kurt]

I agree w/Prach, but......

Does anyone here remove the blower? I never have, and never will. Not that I don't know how, but it's simply beyond the scope. And, if I don't have my work truck w/the full set of tools, spare parts, & other materials, I wouldn't even begin to start.

And, every furnace I've ever torn out, and it's been dozens or hundreds, has a cracked heat exchanger, mounting plate, or something. New, old, or in between. Every one.

Visual inspections of heat exchangers doesn't get you squat. If you wanna know, you have to dismantle the furnace, and that isn't happening.

[Les]

Scott,

I missed the chance to tell you what FAU is.

Doe - Ray - Mei - FAU - Sew - La - Tea - Doe

Brian G should love this one.

[hausdok]

Hi Kurt,

Yeah, I said essentially the same thing. Prach pointed out that if a home inspector did nothing but heat exchanger inspections and everyone else around, including other inspectors doing the typical home inspection, were to refer those to him/her, the inspector would probably make a whole lot more, with less liability incurred, than doing regular inspections, because the inspector doesn't have to do anything but open it up, confirm the damage and then hand it off.

I can understand it, but I guess that the only way that it would work - given the current way that most of the codes of practice are formulated - is for the inspector to sell the heat exchanger inspection up-front, while booking the inspection, and only to expect payment for that aspect of it if he/she actually does find a damaged exchanger. Otherwise, he/she could be accused of an ethical violation for up-selling or for pushing additional services.

Tricky question. Is anyone reading this actually currently pulling blowers to inspect exchangers?

ONE TEAM - ONE FIGHT!!!

Mike

[Jim Morrison]

I agree with Prach and Mitenbuler. An intact heat exchanger is a rare thing. I think Prach once told me he's never seen an intact heat exchanger over four years old....

Hopefully the heat exchanger is OK. Another thing to check is what is stored near the retuen air grilles. I had a client call me with a putrid odor coming out of his air ducts, and it turned out that his daughter was leaving her nasty sneakers on the floor beneath the only return air grill in the house.

Jim

[Martin Lehman]

Thanks for the help guys.

FWIW, I am a member of CREIA (california real estate inspection assoc.)and we have an affiliate member who only inspects pools and he makes a killing.

His name is RickEnglish.

Basically all of us members who dont inspect pools defer to him - and he does an excellent job, much more detailed than any home inspector around.

Oh, and he charges more than most of us inspectors charge to inspect the entire house!!

And he's booked - go figure...

I think you're on to something with the heat exchanger inspections, could be pretty lucrative.

[Les]

Martin,

I agree with Jim, Prach, Mike and Kurt with a caveat; the number of heating days in your house (Calif) do not come close to the number of heating days in my house (Mich). So it is a semi-regional thing.

As a multi-inspector company in Michigan we see lots of cracks and several holes every year. We do not pull blowers and do a visual only. In the past we have done everything from peppermint oil, salt testing, meter testing (several), literally smoke and mirrors, etc. For the past several years it is mandatory to have a register in the plenumn, so we access some units there. It is a little tricky at times.

Our number one call in the fall is from people we have told during an inspection that the exchanger is cracked, rusted thru, plugged, etc and they want us to buy them a furnace. Have not bought one in the past 20+ years.

PS: every G series Lennox I have ever seen disassembled had a crack or hole.

[Terence McCann]

Originally posted by hausdok

Tricky question. Is anyone reading this actually currently pulling blowers to inspect exchangers?

ONE TEAM - ONE FIGHT!!!

Mike

No, that's why God created HVAC technicians.

[hausdok]

S'funny,

The last HVAC tech I talked to thought he was god.

OT - OF!!!

M.

[Bain]

I've had more battles with HVAC guys over the last several months than I can count. Most--around here, anyway--are deplorable. The folks on this board will take more time and get more dirty--i.e. lying on the floor of a basement or crawlspace--checking out a heat exchanger than most of the mutts I meet. The most recent case was a twenty-three year old Rheem installed in a crawlspace. There was an inch of rusted metal flecks in each of the chambers, along with a large crack near the faceplate. This thing was a bitch to look at; the sightline was perpendicular to the heat exchanger. But I stretched out on the yucko crawlspace floor and observed as much as was possible with a mirror and a Streamlight. Slam Cut to two days later. The seller paid for an HVAC company to have a second look. Everything was just peachy. I called the company and explained that their guy missed a potentially life-threatening condition, so they sent out an older, more experienced tech. Didn't find a thing wrong with the furnace. I asked the receptionist chick if her experienced guy pulled the blower. She assured me he did.

So I played my ace. I told the buyer that one of my best pals was a master HVAC contractor, and pretty much the Zen master of heating and air, and that he would reeeaaaally check out the furnace for a reasonable fee, write a letter explaining the furnace had failed, and the buyer would likely walk away with a new furnace.

The verdict? Once the blower was pulled? Five cracks near the burners, and three rusted-out holes toward the top of the exchanger that could be poked through with a finger.

The moral of my rambling, long-winded tale? Find a Zen master you trust if you can, and if not, make certain that anyone who takes a second look at a furnace you have concerns about is told that the blower must be pulled so the heat exchanger can be readily observed.

I don't recommend that any of us pull out blowers, just so you know. The wiring harness has to be removed and things can get screwed up and Carrier thermostats have common wires while most of the rest don't and yes I learned this the hard way by screwing up, and good golly what a awful run-on sentence this is.

[fqp25]

Most easiest way to suspect a cracked heat exchanger: Feel all around the housing of the furnace,(when the burner has been on for a couple of minutes) if there is a spot that is too hot to touch, most likely there's a problem.

As for HVAC techs thinking there GOD; I have a couple in my family, who evolved from plumbers. There is nothing better than being in one of their houses, and complain that it's kind of chilly.

[Bain]

Never heard of that one, Frank. Actually, due to pressure differentials, combustion gases likely won't enter the living-space air unless the crack is really huge.

I used to operate a natural-gas well field. The gas coming out of the well heads had to be compressed because it wouldn't enter the distribution line unless the pressure of the well-head gas was equal to or greater than the pressure within the distribution line. The same principle applies to combustion gases trying to enter the plenum when the blower is operating.

[Jim Katen]

Originally posted by Martin Lehman

. . .QUESTION: What the heck do you think this is?

Are the ducts just really dirty inside and need to be cleaned? Do I need new ducts? Or is it something else?

My wife is pregnant and due in a couple weeks. We are really going to need heat and air quality that is acceptable in our home.

Thanks

I like the dead animal idea.

Once, during and inspection, I fired up a furnace that hadn't been used in years (the guy hheated exclusively with a woodstove). The smell was nauseating. Mice had nested in the house-side of the heat exchanger. We were smelling burning mouse pee, burning mouse flesh and burning mouse babies.

I think the guy threw out the furnace.

Whatever's wrong, I suggest you fix it fast. As I recall pregnant women can be a tad short tempered, particularly during that last trimester.

- Jim Katen, Oregon

P.S. Congratulations. Don't forget to post pics of the baby.

[Martin Lehman]

Hey guys thanks for all the help.[:-thumbu]

I went ahead and did everything you guys suggested.

No dead animals in the flue pipe, it vented well, nothing clogging it, thank God.

No leaks in the duct system, no tears, and no disconnections - the ducts look sound.

So my next step was to check the heat X.

While the furnace was running, I felt around exterior of the furnace housing for a hot spot - what do you know I found one, way in the back of the furnace. This area was much hotter to the touch than any other area of the furnace housing. So to confirm my suspicions, I started taking the furnace apart piece by piece trying to get a better look at the heat x. I took off the draft hood and did not see any cracking, just a whole lot of old and rusted heat x. Next I decided to pull the blower. So I get the blower out and this thing is absolutely filthy (the prior tenants did not understand that there was supposed to be a filter over that big hole under the blower[:-censore). I stick my head up to look at the heat x and there are no holes visible. However, I could not see the back of the heat x where there was that really hot spot I felt. So I grab a mirror and after twisting and turning for what seemed like forever, there it was a large crack about 3 inches long, with about 1/4 inch wide gap.

The next day we had a tech out to replace the old beater with a nice new furnace. No more odors, the new furnace works great.....but....I know I am a perfectionist but the blower that they installed it louder than the last one. Its not that big a deal, it's just kinda loud, where the old blower was not. [:-spin][:-spin][:-spin]