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At first glance, a French Door refrigerator looks like a type of refrigerator that has been around since the 1980’s, a side-by-side. However, a side-by-side has the refrigerator on one side and the freezer on the other. A French Door refrigerator, instead, combines the side-by-side with a bottom-mount freezer. To understand, let’s recap a bit of refrigerator history.
Early Top-Mount Freezers
The first refrigerators with freezer compartments were called top-mounts. The freezer was a small space up top. In early models, there was one door in the front, covering the refrigerator and the freezer, and the freezer compartment was very small with an inner-door of its own.

These freezer compartments could only be used to hold very few items and were prone to icing up. Later, top-mounts developed larger freezers with doors of their own, and anti-frost technologies were developed. The top-mount was and still is the most common type of refrigerator.

Bottom-Mount Freezers
Later came bottom-mount freezers, which were simply a reverse of the top-mount design. Although this kept your oft-used refrigerator items within handy reach, the freezer compartment required stooping to access.

Side-By-Side Refrigerators
The side-by-side configuration solved this problem by making both the refrigerator and freezer vertical: Half the unit is the refrigerator and half is the freezer. This gives more space for freezing and keeps everything within better reach.
Since the doors are more narrow they require less space for swinging open, an advantage in cramped kitchens. The disadvantage is that both spaces are narrow so that larger or wide items may not fit. The extra large pizza box is a problem in side-by-side, but even my small footprint Whirlpool side-by-side will accommodate a fairly large box.

French Door Refrigerator
As said, the French Door refrigerator combines the idea of a side-by-side with a bottom-mount. It has two narrow vertical spaces and one to two bottom spaces. Both the vertical spaces are refrigerator spaces. The bottom spaces are freezer compartments, which are typically pull-out drawers.
Some models have one large drawer and others have one small drawer and one large drawer. The freezer space, overall, tends to be smaller than a traditional top-mount freezer, and space is taken up by an ice maker.

There are also newer French-door refrigerators with 4 doors. These have two vertical spaces on the bottom, instead of drawers, increasing the freezer space and providing shelves for organization.
Models with side-by-side freezer compartments on the bottom require even more vertical space than a regular French door unit.
The First French Door Refrigerators – Late 1960’s?
Most seem to assume that the first French door refrigerators were not marketed until the 1980s. For example this site claims Whirlpool introduced the first French door refrigerator in the 1980’s but discontinued it.
However, I just spied what appears to be a French door refrigerator in an episode of The Galloping Gourmet with Graham Kerr. Unfortunately, since I published this article, the video has been removed.
Why Is It Called a French Door?
The name French door, according to many, derives from the fact that the side-by-side fridge doors open like French doors. This does not make them any different than traditional side-by-side refrigerator/freezer units, which have been around since the 1980s.
Since “side-by-side” was already taken, French door is presumably a sensible name. The French door refrigerator does share a similarity with some French armoires, which have two doors up top and drawers beneath, but other armoires have just the two doors side by side. I have been unable to trace just who coined the name, when, or why.
Advantages and Disadvantages of French Door Refrigerators
Like a side-by-side fridge/freezer unit, the French door has the advantage of a narrow swing for opening the doors. As well, the refrigerator spaces are generally larger than the side-by-side space, making it easier to fit large and wide items. This configuration also means less energy is lost when opening and closing the refrigerators.
When you remove or load items into one side, the other side does not lose any temperature, plus the smaller spaces require less energy to keep cool. The disadvantage is that the spaces are smaller, making it difficult to fit large items.
Although the old-fashioned top-mount is the refrigerator you will most often see in kitchens, French Doors have become the most popular type of new refrigerator to buy. As fancy as they seem, they still do the same job as any refrigerator, and, their higher price tag does not necessarily indicate better functioning.
They have the same disadvantage of the earlier bottom-mount fridges, requiring you to stoop to access the freezer compartment. Units with a double-drawer configuration help, since you can place oft-used items in the top drawer.
Like all types of refrigerators, French doors come in varying dimensions, but they generally require more vertical space, so if your kitchen’s refrigerator space has a cabinet above it, for example, a French door may be too high for you.
On the other hand, as already described, the side-by-side fridge doors require less swing room, an advantage in cramped spaces where larger doors may be blocked by cabinets, etc. The side-by-side refrigerator/freezer combo, however, has the same advantage and typically requires less vertical space, while allowing less cooling space overall. French door refrigerator compartments are generally easier to reach and less stooping is required in general.