90% Furnace, Black Buildup On Pvc, sSmells Like Car Exhaust

Josh_S

Hey guys, as we come out of the cold spell I noticed our furnace left us a present from all the work it had done alongside our boiler to keep us warm. 

Today, I noticed the exhaust no longer smelled clean, it smelled like the exhaust from my truck! It also seems to be leaving a black residue on the PVC coming out of the house. This isn’t burning of the PVC, that was all luke warm, and you can see where I wiped it with my finger on the bottom. Is there anything that would cause this? It also seems to be running a tad hotter than normal, but maybe that’s just me. 

Jamie Hall

It, like your truck, is running rich -- possible intake air blockage?

Josh_S

Jamie Hall said:

It, like your truck, is running rich -- possible intake air blockage?

So it’s pulling a lot of air in, it felt really strong on the pipe outside. It’s reassuring because I’m under the impression it’s less likely there is a bad heat exchanger if the draft inducer has that much suction yet on the intake. I could be wrong though as this is not my field of expertise. Something is definitely not right though.

We will end up having a guy come look hopefully tomorrow. Turning the furnace off and the boiler up for now! Wish the whole house had FHW, lol. 

Sully1266

Have someone look at it ASAP your starting to carbonize. If you had a lot of snow or a ice blockage on  air intake for combustion unit will start to starve for air and start recycling exhaust for air for combustion causing soot build up. Have unit checked out air flow pressure switches should have tripped before carbon got to the PVC exhaust pipes. CO is no joke if you see soot or have a taste in your mouth like blood or chewing a penny all by products of Carbonized Unit.

HVACNUT

I see snow on the ground. Was it deep enough to block the air intake? Either that or intake air condensed outside and at least partially blocked it. Water drips down the hose, onto the PVC. You see where I'm going. 
I would definitely get it checked anyway, meaning a combustion test. 
Does that venting meet the manufacturer's spec's? Looks a little funky.

Josh_S

HVACNUT said:

I see snow on the ground. Was it deep enough to block the air intake? Either that or intake air condensed outside and at least partially blocked it. Water drips down the hose, onto the PVC. You see where I'm going. 
I would definitely get it checked anyway, meaning a combustion test. 
Does that venting meet the manufacturer's spec's? Looks a little funky.

So I had actually called around to a few places today. The snow wasn’t deep enough affect the pipe, or at least it isn’t now. It’s still burning dirty though, the exhaust has a darker hue to it. 

One lady on the phone may have shed some light on the situation though. She said they have been dealing with a lot of high temp limit issues and related over the past few days. She reminded me of the WE energies notice we got a week ago where they had asked utility customers to turn their heat down due to gas supply equipment failure. She further went on to say that they had actually added propane to the natural gas mix to bolster supply and prevent outages. She said they have been working on a lot of these no heats, but said potentially waiting for the propane/NG mix to get used up might be in our best interest as everything else seems fine and functional. 

Perhaps this is a byproduct of this gas mix? My main plenum definitely seemed MUCH more hot to the touch than normal when I first noticed the issue. 

HVACNUT

So have you had a tech out to check combustion?

You blew my mind saying the natural gas utility is adding LP to the distribution system. I didn't know that was safe, possible, sane. I would think that would wreak havoc on a modulating gas valve. Or any gas valve for that matter. 
I wanna scream "FAKE NEWS!" but too many impossible things are coming true.

mattmia2

They do add propane or butane to keep the pressure up under high demand in some circumstances.

You should measure the return and supply temps and compare to the ratings plate.

Josh_S

HVACNUT said:

So have you had a tech out to check combustion?

You blew my mind saying the natural gas utility is adding LP to the distribution system. I didn't know that was safe, possible, sane. I would think that would wreak havoc on a modulating gas valve. Or any gas valve for that matter. 
I wanna scream "FAKE NEWS!" but too many impossible things are coming true.

Tech was out today, he said we have a bad secondary heat exchanger. Clogged and needs replacement. I personally watched the PPM rise on the meter, got to 3,999 and maxed out. I asked him about the propane deal. He said they absolutely 100% added it in as a additive to bolster supply. The utility company was very vague so far but he said the amount of high heat calls and equipment failure is insane. He said:  “See that gas valve? Natural gas only. And it doesn’t stop there. They make a furnace conversion kit for a reason. Propane burns hotter. The thing we will have to wait and see is what the utility company is going to say when they release a statement on what they actually did for those couple days. I have homeowners trying to claim it on insurance but they are innocent until proven guilty” 

I’m shocked but I smell a class action lawsuit. The only thing they’ve said so far is this:

mattmia2

The propane mix won't damage the valve but too much propane might make it burn dirty and soot the hx, or it could have already been misadjusted and sooted the hx and this is coincidental or just made it worse. in theory it can be cleaned but that is a lot of labor. I doubt you could show that the propane is the culprit unless you have a combustion analysis report from before the propane was added.

Josh_S

mattmia2 said:

The propane mix won't damage the valve but too much propane might make it burn dirty and soot the hx, or it could have already been misadjusted and sooted the hx and this is coincidental or just made it worse. in theory it can be cleaned but that is a lot of labor. I doubt you could show that the propane is the culprit unless you have a combustion analysis report from before the propane was added.

Yeah, you are right in regards to our situation, Id imagine ours was an ongoing issue. It’s an older furnace, they go bad. I’m just glad we found out and can move forward. 

The tech is adamant about the issues though, all relating to the higher heat of combustion. I’m just curious to see what’s going to happen with that. I wish he would’ve been a bit more specific on what parts he’s having to replace due to the propane. Apparently expensive enough to warrant insurance claims…

Josh_S

Definitely not caused by a little propane, she needed to go. Now the heat exchanger has a lifetime warranty, is this something that can easily be obtained from Bryant? Furnace is a 350MAV from ‘98

I also think I’m set to replace the burner tube assembly, seems pretty rough 

HVACNUT

Are those parts even available?
25 years is a good run. Replace the whole furnace. 

pecmsg

I pretty sure there available but is it worth the labor?

Sorry but 25 years was a good run!

Get a new furnace.
Get it Properly sized.
Have it installed by a Qualified installer that has been trained in combustion analyses.

John Mills_5

Brand? Carrier or Bryant maybe?