A 4 person sauna is where a home sauna becomes a piece of the house rather than an appliance. Four seats needs real floor area, a heater well past what a normal circuit carries, and a site that can take the weight and the heat. It is also the size most families actually want, which is why the awkward parts are worth knowing early.
The space it needs
Four seats means benches on two or three walls and enough floor to stand and turn between them, plus the heater and its guard. Indoors that is a spare room rather than a corner. This is the point where most buyers move the project outdoors to a barrel or a cabin, because the back yard has space the house does not.
The circuit
A traditional heater for this volume is firmly into dedicated high current territory, which means a licensed electrician, a run from the panel and possibly a panel with capacity to spare. Get that quoted before you choose a cabin. It is the line item that most often turns out larger than expected and it is not optional.
Heat-up, and how people use it
More volume takes longer to reach temperature and more energy to hold, so spontaneous use drops away and sessions get planned. Owners of larger cabins tend to use them less often and for longer. If your pattern is twenty minutes before work on your own, a smaller cabin will get more use for less money.
Indoors or out at this size
Outdoors gives you the space, keeps the moisture and heat out of the house and makes a wood stove practical. Indoors keeps it usable in winter without a dash across the yard, which is the thing that decides actual usage in cold states. Both are common at four seats and the climate you live in should decide it.
Questions people ask about 4 person sauna
Does a four person sauna need special wiring?
A traditional one almost certainly does: a dedicated high current circuit installed by a licensed electrician. Price it before choosing the cabin.
How long does it take to heat?
Longer than a small cabin, and enough longer that most owners plan sessions rather than take them spontaneously.
Is outdoors better at this size?
Often, because the space exists and a wood stove becomes practical. In a cold climate an indoor cabin still gets used more.