# Burn marks on floor joist where furnace ducting is installed...



## Greg74 (Dec 6, 2015)

With the colder weather our furnace has started coming on and running this year. Recently, while I was in our basement back room where the water heater, softener, and furnace are located, I noticed a faint burning smell. I thought that maybe it was the furnace going through its paces as it started running for the first time in a while. Our home is 16 years old.

Then I noticed something: around the floor joist near the end of the ducting that comes from the furnace and runs along the basement ceiling, I noticed small burn marks. They weren't hot and didn't smell like something on fire, but they were there. How long they've been there I can't exactly say. They were only in this area, and nowhere else along the ducting. You can see that at some point fire burned through the goop used to seal the two joists. The attached picture shows the burns. I'm investigating, but who would I call to remediate/investigate the issue, professionally? An HVAC person, fire remediation company, a contractor?

Any advice, experiences, or assistance would be greatly appreciated. Thanks!


----------



## buffalo (Dec 6, 2015)

Ductwork isn't going to get anywhere near hot enough to burn anything. Is that two copper lines zip tied together? My guess is there is a solder joint somewhere close and the burn was created when that joint was soldered.


----------



## oldognewtrick (Dec 6, 2015)

That doesn't look like a burn mark, more like mold. Check to see if the HVAC condensate pa drain isn't blocked.

Oh ya,  to House Repair Talk!


----------



## nealtw (Dec 6, 2015)

I agree with both the other posts, my question is why is the caulk there, so check again for that smell.


----------



## frodo (Dec 6, 2015)

spray it with clorox,  if it is mold it will go away, if it is a burn mark,  it will still be a burn mark


----------



## slownsteady (Dec 7, 2015)

Simply scratching at it with your fingernail will prob tell you a lot.


----------



## KULTULZ (Dec 7, 2015)

Greg74 said:


> With the colder weather our furnace has started coming on and running this year. Recently, while I was in our basement back room where the water heater, softener, and furnace are located, I noticed a faint burning smell. I thought that maybe it was the furnace going through its paces as it started running for the first time in a while. Our home is 16 years old.
> 
> Then I noticed something: around the floor joist near the end of the ducting that comes from the furnace and runs along the basement ceiling, I noticed small burn marks. They weren't hot and didn't smell like something on fire, but they were there. How long they've been there I can't exactly say. They were only in this area, and nowhere else along the ducting. You can see that at some point fire burned through the goop used to seal the two joists. The attached picture shows the burns. I'm investigating, but who would I call to remediate/investigate the issue, professionally? An HVAC person, fire remediation company, a contractor?
> 
> ...


 
It appears as a building cavity (floor joists/wall studs) being used as HVAC supply/return ducting, hence the caulking (pan sheet metal underneath). The stain(s) may be either mold or if supply, soot from an improperly adjusted/serviced furnace (caulking needs to be redone).


----------



## Greg74 (Dec 7, 2015)

Thanks for all the assistance.

As several have suggested, going back down and carefully looking over everything again has lead me to believe the following:

1. The actual burn marks on the joist are probably from when those copper pipes in the bottom of the picture were soldered.

2. I'm beginning to lean towards the mold answer as well. Scratching the caulk with my thumb (where that little hole is with the black around it) doesn't yield anything, however, a foot or so over there are similar marks on the stud between the joists, at both the edges and in the middle. I'm not an expert, but it looks like mold. We had a new furnace installed about 1.5 years ago, so I'm going to talk to them this week. I liberally sprayed the areas with Lysol and will probably have a duct cleaning done soon (including their anti-mold fog treatment).

I've attached a second picture to give a more complete view of the setup.

Thanks for the help.


----------



## slownsteady (Dec 7, 2015)

possibly removed for access, then caulked back into place??


----------



## Sparky617 (Dec 7, 2015)

With the wider view it looks like a burn mark from when the T in the uninsulated copper pipe as sweated together.  The burning smell can be the furnace cooking off dust that accumulated over the summer, especially in systems used for both AC and heat.   If it persists definitely get it checked out.  If it was a one time thing I suspect my analysis is correct.  The dust can accumulate on top of the firebox and as the gas or oil burner heats it up the dust will cook off.  With a heat pump you can get dust on the resistive electrical back up heat, the first time the back-up heat turns on you'll get a burning smell as the dust cooks off.  With baseboard electric you'll get the same smell the first time it kicks on in the heating season.

Heat ducts and water pipes can't get hot enough to scorch wood let alone set it on fire.  That is unless there is an uncontrolled fire going through the ducts.


----------



## frodo (Dec 7, 2015)

the wood duck work is illegal,  ducting shall be metal or gypsum,  if gypsum the air temperature of the duct ed air can not be below 50 degrees


----------



## nealtw (Dec 7, 2015)

We see return air done like that but now the tin has been replaced with some tin coloured cardboard material.


----------



## schlich (Dec 8, 2015)

this is not burn marks it is dust buildup your ducts are not sealed and it is sucking air is threw the cracks iv seen this a lot you just need to get some duct sealent and paint it on not only will this fix your problem it will put the heat that you pay for where it belongs in your househere is a vid that will help you fix it [ame]https://www.youtube.com/watch?v=aCCWAmESK4w[/ame]


----------



## frodo (Dec 8, 2015)

schlich said:


> this is not burn marks it is dust buildup your ducts are not sealed and it is sucking air is threw the cracks iv seen this a lot you just need to get some duct sealent and paint it on not only will this fix your problem it will put the heat that you pay for where it belongs in your househere is a vid that will help you fix it https://www.youtube.com/watch?v=accwamesk4w



pookie!!!!!!






thats what we call it


----------



## KULTULZ (Dec 8, 2015)

schlich said:


> ...this is not burn marks it is dust buildup your ducts are not sealed and it is sucking air is threw the cracks iv seen this a lot you just need to get some duct sealent and paint it on not only will this fix your problem it will put the heat that you pay for where it belongs in your house


 
Correct. This appears to be a return ducting using a floor joist cavity in lieu of metal ducting. It is quite common in this area (Eastern Panhandle WV). It (the fabricated duct) should be lined (IMO) with THERMO-PAN properly fastened and sealed. 

This installation is showing a poor installation and a poor quality of caulk (not mildew resistant). The caulking should be redone and use a sealant as suggested to try and completely close the duct. It will only draw unfiltered air into the air handler.


----------



## Sparky617 (Dec 8, 2015)

Even with the ducts sealed some dust will make it to the furnace. Sealing the joints will definitely help though.  My childhood home and my first two homes had the air filters right at the furnace.  My last two homes have them right at the return grates, which keeps the ducts quite a bit cleaner.  Using the joist bay for a return duct was fairly common back in the day.  I don't know if it is against code today, but even if it is if the house was built when it was built according to the code you're fine.  Just seal up those joints.  OH and get your furnace serviced by a professional.


----------

