When planning a sauna’s size, figure you’ll need at least 2 feet of bench space for each bather; ideally, bathers should be able to recline, so, if possible, allow 6 feet in one direction.

Be aware that the size dictates not only how many people can comfortably sauna at a given time but also the output capacity of the heater you’ll need.

Most saunas have benches at two heights, an upper bench, about 36 inches high, and a lower bench, about 18 inches high. Upper-bench widths are typically 18 to 24 inches.

The lower bench has three functions: it serves as a step, provides a footrest when one is seated on the upper bench, and offers a significantly lower temperature zone for when the upper-bench area feels too hot.

Some manufacturers make a sliding lower bench that eases cleaning. Most saunas have removable duckboard flooring; some offer flooring that is made of flexible, web-like polymer sections that simply snap together.

Some saunas have windows; many have a glazed door that provides an open feeling. Glass may be clear, opaque or even etched with a design. But remember: the more windows, the greater the heat loss. Choose energy-saving glazing that has a 1/2- to 1-inch air space between the two outer layers of tempered safety glass.