Furnace goo?

[A Little Weird]

Hi! I saw this group and wondered if anyone here could help me identify some mystery goo that's been forming on top of my furnace.

I first noticed it back in December when I went to change my filter. There was a little bit of white stuff on top of the furnace - it looked a lot like paint splatters but I know it was not paint. It seemed odd but I didn't really think much of it. When I went back to change my filter this month, there was a lot more of the goo.

I would really like to know what is causing it and if it is a safety issue of any sort. I don't have a lot of money to call someone right now so I thought I would just do some research but I don't even know what to look for (googlling 'furnace goo' didn't help me). Does anyone know what this is called or what might be causing it?

[jeff47]

1. Can you describe it in a little more detail?

Is it solid or liquid? Is it sticky? Is there anything similar directly above where you're finding it on the furnace? Does it look like the stuff they used to seal the air ducts at the joints?

[A Little Weird]

4. Solid

It's solid, not sticky and when I touch it, it crumbles into a fine powder. Looking above, it looks like there's more around the joint of the vent (the smaller pipe going straight up, not the larger ducts that are going throughout the house). Does that make sense? I am sorry I'm not explaining this better.

[jeff47]

5. My guess from your description so far is it's duct selant

They paint a liquid over the joints in the heating system, which then dries to a solid compound. It's also frequently used to seal the boot (the part of the vent behind the drywall) to the wall.

If it is duct sealant, the worst effect would be a slight reduction in the efficiency of your heating system - a little bit of air could leak from the boot into the space behind the drywall, instead of being pushed into the room. If this is the case, it's a very small problem that's not worth worrying about. Since it's falling off, the installer probably used too much and what remains on the boot may keep it sealed. If there is a leak, it would be very small.

Another candidate is drywall compound or plaster, but that usually falls off as a large chunk or as a powder - meaning a powder before you touch it.

But back when I built houses we left the HVAC work to our really good HVAC contractor, so I could be wrong.

[A Little Weird]

7. That doesn't sound too bad

But I tried a different search based on someone's suggestion downthread and I came up with some results that indicate it could be a residue caused by improper venting. I hope it is just duct sealant but I guess I should have it checked out. Thanks for responding. Next time I will try to post pictures - it was much harder than I expected to describe the problem.

[NYC_SKP]

2. Take and post digital pics, here but also at HVAC discussion boards.

All the trades, electrical, plumbing, HVAC (heating and air conditioning) have discussion boards, like DU, where people post pics and ask questions.

Your answer is probably out there.

It could be residue of combustion by products, the need for a new filter or a burner cleaning, or some external problem like mold.

Try posting pics and description and mention the make and model of your furnace, and if it's gas, electric, or fuel oil.

good luck.

[A Little Weird]

8. I think you're right

I went to some sites that described a problem of residue buildup due to improper venting. Thanks for taking the time to respond - I will try photos next time.

[BootinUp]

3. google: "white furnace residue"

It returns a few hits...

I don't know what would cause it expect for some kind of condensation or leak somewhere.

[A Little Weird]

6. Thanks

What a difference a search term can make!

Looking over a few sites leads me to believe this is not an uncommon problem but opinions seem to vary on how serious it is. It is either a common wintertime problem that I can safely ignore or a flaw that can ruin my furnace and/or lead to a potentially fatal carbon monoxide buildup.

So I guess I should stop ignoring it and try to save up some money to have someone come look at it.