Chimney access questions.

[1870farmhouse]

Ok so I have an 1871 house. The chimney was added later because where the chimney now exists you can see in the attic that they boarded up a window to build the chimney.
I’m including some photos to hopefully see if anyone can tell me what these panels are.

So the chimney has 2 separate flues, one is 6.75 x 7” and that goes down to the basement, because of this I believe this chimney was built in the 1920’s-1940’s to facilitate smoke from a oil fueled heating system and possibly added the fireplace for Aesthetic reasons.
The second flue is 11 x 6.75” which services the fire box.
The basement oil heater is long gone but it’s clear where it once stood and the flue connection has been closed off and stuffed with insulation.

The first photo is outdoors showing 2 access metal panels attached via 2 wingnuts each, if I knock on them it’s obvious there is empty space/void behind them and they seem to be about 2’ under the firebox brick floor.
Second photo shows the firebox with my encore tilted to the side as I’m about to take it apart to replace with an entire new damper assembly. In this photo you can see in the back middle of the firebox a rectangle shaped housing.
Third photo is closer to the rectangular housing.
Forth photo shows that with a light tap of my hammer(2-5lbs of force) the housing flipped up to show access below. I’m guessing to the void area that can be accessed by the 2 metal panels from outside.

My first question is, does anyone know for certain what this is designed for? Is it to bring fresh air to the firebox?
Second question is, I’ve read that bringing fresh air to feed the stove is most efficient instead of the fire taking air from your house that already has been heated, so could I feed the wood stove fresh air needs through this housing that certainly connects to the outside via those 2 panels on the chimney wall?
Third question, has anyone fed their stove with indoor air and switched to feeding the stove with cold outside air and seen a big difference in heat retention?
Forth question, would feeding the stove outside air be any safer/more unsafe regarding carbon monoxide or any other dangers?

I read somewhere that it could possibly be an ash trap where you could more easily shovel the ash out of those external panels without getting the interior dusty/ashy but I don’t know.

 

[begreen]

Looks like an ash trap. It might be a path for installing a fresh air feed but be sure the intake doesn't ever get blocked by snow. Outside air can help reduce a slight exhausting of room air up the flue. I think I read that this is less than 100 cfm, but don't hold me to that. There may be more than that air exchange even without the stove running if the house is old and somewhat leaky in several places.

 

[1870farmhouse]

Looks like an ash trap. It might be a path for installing a fresh air feed but be sure the intake doesn't ever get blocked by snow. Outside air can help reduce a slight exhausting of room air up the flue. I think I read that this is less than 100 cfm, but don't hold me to that. There may be more than that air exchange even without the stove running if the house is old and somewhat leaky in several places.

I’ll post photos down the trap door below.

Good advice on snow not blocking the outside panels, I’m in SE Pennsylvania 1 mile from Delaware state line so 2’ of snow is quite rare these days but if I use this as a fresh air supply I’m thinking of either drilling small holes in one of the outside panels or find a Louvered panel of the same size.
The trap opening on the firebox floor is 5.5 x 8.5”

Photos show it’s certainly an ashtrap with a bunch of ash piled up with about 12-18” of clearance from top of ash pile to the bottom of the trap door.
I couldn’t see the exterior access doors so I believe the ash is covering them up.

The dedicated fresh air stove intake is 3” underneath the rear heat shield so the ashtrap dimensions easily support a 3” pipe.

 

[GG Woody]

Both inserts I have owned in two different houses have taken combustion air from that clean out, seems to work good.
Might as well use cold outside air, beats cracking a windows or competing with other exhaust devices in the house.

 

[25yearsof imstallation]

These are all taking there combustion air from outside and they work perfectly