Wall furnace installation in older house

In an apartment that uses a gas-with-gas stove (cooking and heating) and there's a pipe exiting the heater part of the stove and going to a chimney that's to the right of it. Gas-with-gas stoves haven't been manufactured for awhile, but that kitchen would still need heat. A modern gas wall furnace would fill the bill if a new gas stove was put in, but I have a question about the venting for the wall unit. It seems they use a concentric pipe that goes through the wall to the outside providing combustion air and burned gas exhaust. The only practical place to hang this furnace would be on the wall right next to the stove where the chimney for the old stove is. So to get to the outside of the building, you have to go through the wall into the chimney then through the chimney on the other side to the outside wall. Would such a long run defeat the purpose of the concentric pipe?
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