Yes in the time of yore the brick chimney was the flu, with both floors sharing the same chimney. There was no clay or pipe flue system such as there is today.
All the fire places or stove locations in the Borden home at 92 used existing chimneys, that is to say, the ones that were placed there when the house was built which are the same today.
Now, the reason why the fireplace was so close to the door was because it had a smaller mantle. The black mantle there now was not designed for that room. (sitting room)
As far as the traffic pattern is concerned let's look at one of the floors, the first floor. (Since the second was an exact copy.) When you entered the house via the back door, you went into a common hallway which led to the entry door, which led into the kitchen. When you left the kitchen and walked towards the front of the house you did so through the sitting room, which led to the front hallway and the front door.
Now, where the dinning room exists today on the first floor is where the bedrooms existed. There were two bedrooms on each floor. (or apartment) Just before leaving the kitchen to enter the sitting room there was a door on the right which led to one bedroom. Once in the sitting room, and just the other side of the sofa, there was another door which led do the 2nd bedroom.
Andrew borden left the bedrooms intacted on the 2nd floor. One became Emma's room, and the other became Abby's clothes room.
So, before the house was split up, and on both floors, you came into the house via a common back hall or a common front hall. The common back hall lead into the kitchenS. The common front hall had two entries into each apartment. One lead to the parlorS and the other, straight ahead, into the sitting areaS, or sitting roomS. So it was a straight run from kitchen, through sitting room, through front hallway and out the front door. On the second floor it was a straight run from kitchen, through sitting room, through front hallway, down the front stairs and out the front door.
The one thing that may confuse us, and we must consider the times, was that the bedrooms were very tiny. As a one family home 92 Second Street had ample room. But as two apartments, each apartment was not that large at all.
Now, mentioning the size of the bedrooms. In today's world people have become vulgar and crass in the size of bedrooms. Spoiled and greedy is putting it mildly. Look at the homes they are building today. Huge McMansions. Some with bedrooms the size of some older homes. Considering the pine box we all end up in when our time is up, these obscene buildings speak to pampered indulgence and coddled personas with skewed perceptions of what is normal and what is excessive. If you have the money than I suppose you should go for it. But I know several friends who live in such places and owe the world a fortune. And though they appear successful, life is passing them by as the struggle to make their monthly mortgage.

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