What was that hole I found in my chimney?

[Jon1270]

The interior brick around my fireplace is mostly covered by wood paneling from some earlier decade's remodeling project. I'm cutting the paneling back to meet necessary clearances for a new insert, and made an odd discovery. My chimney has two flues, one for the fireplace and another for the furnace and water heater. House is late 50's construction. Hidden behind the paneling to the left of the fireplace I found an opening in the face brick, about 9" square, shaped around a neat metal frame. Before putting up the paneling, someone had buttered a few firebricks with mortar and shoved them in there haphazardly to plug it up. The bricks stuck out far enough to be a problem, so I broke them free and removed them. The neat opening continued all the way through the chimney brick, giving me a clear view of the furnace / water heater tile liner.

I have already bricked this up again, much more neatly than the first time, but... what the heck was that hole in my chimney for?

 

[firebroad]

Photos??
Does it appear to have been hinged at any point?

 

[Jon1270]

Nope, no hinge-like bits anywhere. Just a light-gauge metal frame with rounded corners and a couple of dimples to anchor it in mortar.

 

[firebroad]

Well, that probably rules out inspection port. And if it were for a stove pipe, it is the wrong shape. I'm stumped, although I did once see a fireplace with two louvred openings on either side of the firebox that were believed at the time to be beneficial for heat dispersal somehow.

However, I found this link:
http://www.ehow.com/how_6638615_filling-between-fireplace-vent-brick.html

 

[Jon1270]

I did once see a fireplace with two louvred openings on either side of the firebox that were believed at the time to be beneficial for heat dispersal somehow.

That was my first thought, too. The original fireplace was a heatform-type prefab steel unit, which do sometimes have those sorts of heat distribution channels, but the theory doesn't seem to fit in this case. The hole doesn't connect to it, and doesn't have louvers.

It seems really odd that they'd leave they'd leave an opening to the furnace chimney tile - a clear carbon monoxide hazard when the mortar between tiles starts to fail.

 

[firebroad]

Here's a thought--maybe a former owner had a safe installed there, covered by a painting, just like in the movies. Of course, I am not sure how hot that stash would have been...

 

[Jon1270]

Well, it looks like that opening must have been intended to transfer some heat from the Heatform-type fireplace out to the room, as firebroad suggested, though I doubt they ever had much effect. There were three more of them behind the paneling. If they ever had louvers (and they must have), they are long gone; all the holes have been filled with bricks.

The impetus for my current project was the discovery that the original fireplace had rusted into uselessness. My guess is that the Heatform started to perforate sometime back in the 60's or 70's, shortly before the paneling was installed. When the liner rusted through above the smoke shelf, these heat-circulating openings probably started to send some smoke into the room instead of up the chimney. So, they bricked them up, which looked like hell, which in turn prompted the paneling.

That's my theory, anyhow.