Where is the air coming from.

[mm]

How do I accurately figure out where air is blowing out from, from my furnace flue area, which is next to my hot air duct.

I'v used a match, but it keeps blowing out. Tonight I took a pencil and thumbtacked a thin strip of cellophane-like stuff to the end of it. Later I added a narrow strip of thin cloth. They blow like crazy when the pencil is on the right side of the flue, but I can't seem to narrow down where the origin is.

The furnace is a rectangular box, with the heated air duct attached to the top and going up from there. The fire exhaust comes out the front side just below the top, into the flue collector, a metal box which was rebuilt last week and is 14" wide, almost as wide as the furnace, and 5" high and 8 inches deep. On the top side of it connects the 6" round flue.

When the pencil and its flags are on the left side of the flue, no breeze is detected. But in front of the metal box in the middle, and anywhere above the box to the right of the flue, the "flags" on the pencil blow around like crazy. I'd like to narrow down where the air is coming from.

Background: You've all convinced me that I need to buy a new furnace, and I will this year, but I don't want to rush, so I'm still using my old oil furnace until I have time to get recommendations, prices, etc.

As I described in a previous post more than a week ago, I had the flue collector repaired by a welder. As Eric predicted, when he welded one place, he made a new hole next to the weld.

So I filled all the holes with GE Red Hi-Temp Silicone, which it says is good to 650 F intermittent (and a tube from 10 years ago said it was good to 600 F.) And it doesn't seem to get anywhere near that hot. And the "glue" is certainly in good condition only a week later, though perhaps it's not sticking everywhere I think it is. Maybe air is escaping. I'll put on more layers, but I'd like to know first where the leaks really are. It's not that cold and I won't be running the furnace until the leaks are stopped.

When the burner starts, no air comes out through the repaired

[Ed Pawlowski]

You can buy a smoke pen or light one of those incense things that smoke. They will generate smoke, but by smoldering, no open flame to blow out.

[mm]

Good idea. I have an incense stick. No, I diddn't buy it. I'm no hippie. It was probably in the apartment I used to have when I moved in 38 years ago. I put it in a vase and it's still there, I think. (I've only moved once since then.)

I figured it might come in handy, and 38 years later, it will.

If that doesn't work, I'll look for a smoke pen.

[mm]

And thanks.

[mm]

I found it. It's either an incense stick or a very tiny corndog.

[gfretwell]

Get some small diameter hose, 3/8 or so. Hold one end up to your ear and probe around where you think the air is coming from with the other. When you get close it will sound like a hurricane.

[mm]

Also a very good idea. In my case maybe a better one because my 30 year old incesnse didn't burn well.

I will check for wind tomorrow again, but tonight I had decided it was coming from the outer surface of the firebox, at the top by the heat exchanger, and when it cooled and I put my hand in, fingertips up, it turned out there was a wide but shallow opening from the warm air duct. Not from the exhaust gases at all but from the warm air duct to the heating ducts. That explains why the breeze was only there after the main blower fan turned on. I don't remember if I had this before. I guess I must have.

Surely it's okay to plug this hole, right?

[Stormin Mormon]

I usually run my hand an inch or so away from the flue or duct. I can feel the escaping air.