I still don't understand my oil furnace!

[mm]

I still don't understand my oil furnace!

I'm going to buy a new furnace in the next 9 months but I'd still like to understand the one I have now. Maybe the new one will have the same parts.

When the flame goes on, no noticable air comes out of any of the connections, but (I've patched all this now, but it used to be that) when the air circulating fan comes on a minute or two later, air blows out from lots of places. Is this normal?

1) One of them was under the edge of the flu collector. I know that wasn't normal, and I'm not asking about that. I caused it when I took the part off and when putting it back on, I had a surprisingly hard time positioning it correctly and the sealant I'd put on got spread around too much and the amount wasn't enough everywhere.***

2) Another place was just above the furnace end of the flue collector, above it but not related to it, at the very top of the furnace. Only on the right half for some reason, I couldn't see it and I didn't bother to get a mirror, but I could feel a slot at least a quarter inch front to back and 6 or 8 inches wide, where it seemed the furnace flange for the air output duct was somehow not as wide front to back as the duct itself was. How could that be! And why only one one half? Anyhow, I also filled that with hi-temp silicone.

3) And most interesting, after I sealed those two areas, lots of air was still blowing out when the blower was on, from around, I don't know what you call it, the fire window tube? There is a "tube", about 5" in diameter, with a spring loaded metal door, which one can lift up with a tool (because it's hot) and see the fire itself in the fire box. (This tube is about 6 inches above the whole burner thingy, the transformer, oil pump, electronics etc.) A few years ago, when the furnace was mal-adjusted, soot piled up in this tube. The left half of the circumference of this big tube, at the base of it, had air blowing out when the burner and fan were on. Enough to be easily felt with my fingers.

Since right on the other side of the wall was the fire box, was this air exhaust air?

It didnt' smell like oil, or feel oily or dirty, but if the burner is set up right and the combustion is complete, does the exhaust air from an oil furnace have a smell?

And why would more air be coming out of the fire box when the air fan is on then before it goes on? Isn't the firebox and flue and chimney separate from the air in the cold and warm air ducts? I scraped and vacuumed the 6 or 7 oblong tubes in the heat exchanger and they seemed hard as iron, no rusting or leaks there. If there were leaks, where would they be?

Thanks.

***which I posted about here a couple weeks ago, which had rusted through because my humidifier dribbled water on it for years. I had another layer welded onto three sides and then I used hi-temp silicone sealant** to patch the smaller holes the welding caused. When I went to screw the thing back to the furnace, I had a surprisingly hard time positioning it correctly and the amount of sealant I'd put on wasn't enough everwhere. I could have used "furnace wool", I think it is called, which is like a gasket, but online the only thing I found was a whole roll for 22 dollars, and I didn't take the time to hunt for it locally. Partly because I'm not going to take this furnace apart again.

**The hi-temp silicone in 4 oz. tubes is only available at auto parts stores, not the big box hardware stores I've been to. Maybe the big box tubes has the stuff in caulking tubes, I don't remember. But a little of this goes a long way.)

[salty]

When you wake up dead from Carbon Monoxide poisioning, it will all make perfect sense to you.

[Heathcliff]

It's been a long time since I had an oil burner furnace, and I am having trouble picturing yours from your description, but see if this helps. For any oil (or gas) fueled, forced-air furnace, air flows through it in two ways. Combustion air is drawn from the room (unless it's one of those newfangled ultra-efficient models that pipes in outside air; I'm guessing that is not the case for you), enters the flame area, then goes up and out the flue. Meanwhile, air is drawn from cold air return ducts throughout the house, through ductwork, and into the furnace where it is warmed up, and then the warm air is distributed through more ductwork to warm-air ducts located throughout the house. These two air streams go through the furnace, but they should not mix. The heat exchanger within the furnace is where the heat transfer takes place. On an oil furnace, I suspect that if there was something seriously wrong such as the flue plugged up or combustion air mixing with house air, you would smell something.

I have two recommendations. One, stop putting caulk or sealant or whatever on your furnace. It shouldn't need it. Two, get a carbon monoxide detector (roughly $25) and put it somewhere a little ways away from the furnace. If there is a majorly dangerous problem, it will sound. Lastly, if you have still have questions or concerns about it, get a furnace repair person to check it out and explain it to you.

[mkirsch1]

Waking up with headaches in the morning? Don't worry, it will be all over soon, and understanding the furnace will be the least of your problems.

If you want to learn about your furnace, call a repairman, watch what he does and ask questions. It was the best $74 I spent this year. I learned that I have a 2-stage furnace, how a 2-stage furnace works, and why the "problems" I thought I was having were simply normal operation of a 2-stage furnace.

[Jules]

I bought some sealant designed for HVAC last year in the cartridges that fit the smaller caulk guns - gray stuff, quite 'wet', had an almost grainy texture to it. I assume it's designed to not release horrible fumes into the duct system :-) My local farm supply place does it, but I'm pretty sure I've seen it in HD, too.

[Van Chocstraw]

I don't think you should be touching a furnace. Get a professional.

[mm]

Thanks. I'll check.

Although I think I'm done for this year.

Some or all of the places I put the hi-temp stuff don't need hi-temp, which I think says it is good to 600F.

Even the flue collector, the part just after the exhaust gas leaves heat exchanger and before it gets to the flue, about 10 inches away, doesn't seem to get as hot as my clothes iron. When I spit on my finger and touch the iron, the water sizzles (That's the normal method to see if the iron is hot.) but on the front of flue collector spit just sits there and evaporates faster than it would at room temp. Since the top iron temp is about 212^, that makes the front of the collector less than that.

But the oil company guy tried to tell me that it was so hot, the requiements to make one were so stiff that I wouldn't be able to find someone to do it. He wanted me to buy a new furnace that day.