Air blowing out of a furnace sight tube?

[Brandon Whitmore]

Is there any other reason that air would be blowing back out of an oil furnace sight tube other than a damaged heat exchanger? When the blower is running without the burner on, air blows back out when the sight tube is open. Seems pretty fishy and odd to me-- I can' t recall ever seeing this. The only thing that has me second guessing my call is the fact that it was serviced, and a heat pump added to the system 8 months ago.

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[Jim Katen]

Is there any other reason that air would be blowing back out of an oil furnace sight tube other than a damaged heat exchanger? When the blower is running without the burner on, air blows back out when the sight tube is open. Seems pretty fishy and odd to me-- I can' t recall ever seeing this. The only thing that has me second guessing my call is the fact that it was serviced, and a heat pump added to the system 8 months ago.

Perhaps when the blower is running the furnace room becomes depressurized.

- Jim Katen, Oregon

[Brandon Whitmore]

Perhaps when the blower is running the furnace room becomes depressurized.

4200 sq. ft. 2 level house built in 1970. The furnace is in the center of the daylight basement and not fully closed in, so I doubt it. It was blowing like air coming out of a heat register. Very odd..........

[Kyle Kubs]

Perhaps when the blower is running the furnace room becomes depressurized.

4200 sq. ft. 2 level house built in 1970. The furnace is in the center of the daylight basement and not fully closed in, so I doubt it. It was blowing like air coming out of a heat register. Very odd..........

I would say you got it on your first guess. The heat exchanger likely has a big hole in it. But, like Jim said, even under the circumstances you describe, if the have the blower cabinet door off while your doing this it could just be drawing from the chimney.

How old is the furnace?

Where is the fan in relation to the burn chamber? Under or behind? I ask, because I had one with the blower fan in back of the heat exchanger and with the blower compartment open, looking through the fan blades I could see the flames in the burn chamber... and it was only around 10 years old. Unfortunately it's a lot harder to see up through the fan if it's under the burn chamber.

[Jim Morrison]

I can typically smell combusted oil in the house if the heat exchanger is compromised. Did you notice anything like that?

[MechAcc]

With the blower door on the furnace if the air starts immediately and extinguishes just as quickly then you most likely have a heat exchanger leak. Either a crack or rust perforation.

[Brandon Whitmore]

How old is the furnace?

Where is the fan in relation to the burn chamber? Under or behind? I ask, because I had one with the blower fan in back of the heat exchanger and with the blower compartment open, looking through the fan blades I could see the flames in the burn chamber... and it was only around 10 years old. Unfortunately it's a lot harder to see up through the fan if it's under the burn chamber.

Hi Kyle,

Furnace is original to the home. (early 70's).

The blower was behind the burn chamber, but I didn't think to look up through-- thanks for the tip.

[Brandon Whitmore]

With the blower door on the furnace if the air starts immediately and extinguishes just as quickly then you most likely have a heat exchanger leak. Either a crack or rust perforation.

The air blew through as soon as the blower was turned on, and continued 'til I turned the blower off. This was with the blower door installed. I didn't try anything with the door off. This was a lucky catch if it's an exchanger issue. From now on, I'm going to check for air blowing through this port when the blower is running.

I am going to try to keep in touch with the buyer, and will report back if I find anything out.

[Brandon Whitmore]

I can typically smell combusted oil in the house if the heat exchanger is compromised. Did you notice anything like that?

I didn't notice that smell. Of course, I didn't leave the thing running all too long- it was 90+ degrees yesterday, and the air blowing out was enough for me to recommend a heating contractor.

The oil furnace is the emergency furnace- a newer heat pump has been installed within the last year. The heat pump installer needs to come back out and fix some issues anyways.