In older houses located in colder climates, it was fairly common to have one chimney with two or more separate flues. This would allow a homeowner to vent, say, an oil-burning appliance as well as one, two, or even three wood-burning stoves/fireplaces.

Old houses frequently feature two or more chimneys primarily because they were built before the advent of modern central heating systems. In the 18th and 19th centuries, each main room of a house required its own individual fireplace for warmth, and each fireplace needed its own separate flue to safely vent smoke and combustion gases out of the building. Placing chimneys at opposite ends of a house helped distribute heat more evenly throughout the structure. Additionally, separate chimneys were often used to distinguish between different types of fuel or functions; for example, one chimney might serve the formal parlors and bedrooms with coal or wood fireplaces, while a second chimney was dedicated to the kitchen's heavy-duty cast-iron stove or cooking range. These houses were not "airtight" like modern homes, so multiple flues also helped with natural ventilation and draft. Today, these twin chimney stacks are seen as a hallmark of historic architectural styles, such as Federal or Georgian, though many have since been repurposed to house modern furnace vents or gas fireplace liners.