SAUNA PLAN DUILDER— DRAW YOUR SAUNA TO SCALE IN SECONDS

A comfortable home sauna is about 5' × 7' with a 7' ceiling — roughly 245 cubic feet, seating four on two tiers. Below that, 4' × 6' seats two to four and is the smallest size that still takes a proper two-tier bench. Above it, 6' × 7'6" seats up to ten and 8' × 8' seats twelve. The number that actually constrains you is not floor area but bench run: every seated person needs 24" of bench width and 20–24" of depth, so a long narrow room seats more people than a square one of the same area. Type your real dimensions into the builder above and it will tell you how many seats fit before you frame anything.

Upper bench: 24" deep at about 39" high. Lower bench: 20" deep at about 18" high. Twenty inches is the minimum depth anyone can sit on properly; 24" lets you sit cross-legged or lie back. The upper tier should overhang the lower by around 3", which is why a well-drawn plan shows the hidden strip of the lower bench dashed. Two tiers beat one for the same reason a sauna has a ceiling height rule — the top bench is where the heat is, the bottom bench is where you go when it is too much. Design benches from the ceiling down, not the floor up: the head zone between the upper bench and the ceiling is what has to land right.

Two people: 4' × 4' to 4' × 6'. Four people: 5' × 6'6" to 5' × 7'. Six people or more: 6' × 7'6" and up. These assume a 7' ceiling and a two-tier bench along the longest wall. Barrel saunas seat fewer than their footprint suggests, because the curved walls eat bench depth at the ends. Commercial rooms scale differently again — a 14' × 20' room seats around thirty and needs a bank of heaters rather than one big one.

Allow 24 inches of bench width per person, and count only the bench runs, not the floor. A 5' × 7' room with an L-shaped bench gives about 12 feet of usable run, which is six seated places or four with room to stretch out. A bench run shorter than 36" seats nobody usefully. Lying down changes the maths entirely — one person reclining occupies a full 6' run. The plan builder counts seats for you as you change the layout, and shows upper and lower tier counts separately.

Seven feet (84 inches) is the standard, and lower is usually better than higher. Heat stratifies, so every inch of ceiling above the upper bench is volume you are paying to heat and never sitting in. The constraint that matters is the gap between the upper bench and the ceiling — the head zone — which wants to be 43–47". A 7' ceiling with a 39" upper bench lands at 45", right in the middle. Ceilings above about 8' need a noticeably larger heater for no comfort gain, and some heaters specify a minimum room height of their own — the HUUM DROP, for instance, requires 1900 mm.

The rule of 200 is a Finnish rule of thumb for bench and heater height: your upper bench should sit so that bathers' bodies stay inside the hot "löyly" zone, with feet at or above the top of the heater's stones. In practice it is the same thing the plan builder enforces through the head zone — the gap from the upper bench to the ceiling landing at 43–47" on a 7' ceiling. You will also see it written as the "rule of 230" (the top bench no more than about 230 cm from the floor) or "the law of löyly". They all describe one idea: sit in the heat, not above it. Set your bench too low and you are in cool air; the tool draws the head zone to scale so you can see it before you build.

The dimensions that matter are the interior clear dimensions — the usable space inside the finished walls. A sauna described as 5' × 7' should give you 5' × 7' of actual room to sit in; the exterior footprint is larger by the wall assembly, usually 4–8" per wall, so that same room is roughly 5'8" × 7'8" on the outside. Always design and size the heater from the interior number, because interior volume is what sets bench run, seat count and kilowatts. The plan builder works entirely in interior clear dimensions and draws the wall thickness outside them, so what you type is what you sit in.

A sauna door must open outward, always, and glass costs you heater capacity. Outward swing is a safety rule, not a preference — nobody should ever be trapped by a door that opens against them. On heat: every square foot of glass behaves like an extra 3.94 cubic feet of room, so a typical 10 ft² glass door adds about 40 ft³ of load, which is a meaningful slice of a 3 kW step. Put the door on the wall furthest from the upper bench so people entering do not dump cold air onto whoever is lying on the top tier. The plan builder draws the swing arc to scale and recalculates the heater when you add glass.

Divide your room volume in cubic feet by 35 to get the kilowatts. A 5' × 7' room with a 7' ceiling is 245 ft³, so 245 ÷ 35 = 7 kW, and you would buy the 8 kW because that is the size that exists. Then adjust: add 3.94 ft³ for every square foot of glass, 4.92 ft³ for every square foot of exposed stone or tile, and multiply the whole thing by 1.3 if the room is uninsulated. Never go below 3 kW. The plan builder does all of this and then checks the answer against the manufacturer's published volume range for the specific heater, which is where most online calculators stop short.

On a 7' ceiling: a 4' × 6' room takes about a 6 kW heater, a 5' × 7' room an 8 kW, and a 6' × 8' room a 9 kW or larger. These follow the 1 kW per 35 ft³ rule and assume an insulated, wood-lined room with a normal amount of glass. They deliberately run one size above the common "1 kW per 50 ft³" dealer charts, because those undersize rooms that have a glass door or any cold surface — the most common reason a new sauna never quite gets hot. Add a step for a full glass front, a barrel or an uninsulated outdoor room. A chart gets you close; the plan builder checks the answer against the specific heater's published volume range, which gets you right.

Roughly 1 kW per 35 cubic feet, which is the imperial version of the Finnish 1 kW per cubic metre rule. That figure assumes an insulated room with wood-lined walls and a normal amount of glass. It is a starting point, not a specification: two rooms of identical volume can need heaters a full step apart if one has a glass wall and the other does not. Cold surfaces, not air, are what a sauna heater actually fights. Charts that use 1 kW per 45–50 ft³ will hand you a smaller heater than we will — fine for a sealed, all-wood box, risky for anything with glass.

Only the very smallest ones, and not well. A 120 V circuit tops out around 1.5–1.8 kW, which by the 35 ft³ rule serves a room of roughly 50–60 cubic feet — smaller than a 4' × 4' × 7' cabin. Traditional saunas of any usable size run on 240 V. If a 240 V circuit is genuinely impossible, that is a real constraint worth designing around from the start rather than discovering after the room is framed, and it usually points at infrared rather than a stove-and-stones room.

An 8 kW heater at 240 V draws 33.3 amps and requires a 50 A two-pole breaker on 8 AWG copper. The reason it is 50 A and not 40 A is the continuous-load rule in the NEC and CEC: a breaker may only carry 80% of its rating continuously, so you size the breaker at 125% of the load. Manufacturer tables often quote the raw draw and get this wrong. A sauna needs a dedicated circuit, and above about 9 kW — roughly a 60 A circuit — the panel and service capacity genuinely need reviewing before you order anything. The plan builder prints the circuit count, breaker size, poles and an indicative wire gauge on the drawing. An electrician sizes the real conductor against your actual run length.

Electric for anything indoors or on a timer; wood for an outdoor room where the fire is part of the point. Electric heaters are sized in kilowatts and controlled to the degree, they can be pre-heated from a phone, and their clearances are small enough to fit tight rooms. Wood stoves are sized by room volume rather than kW, need a chimney, a hearth, a non-combustible floor protector and clearances measured in feet rather than inches — an unlisted stove needs 48" on every face. The plan builder will draw either, and switching fuel redraws the clearance zone and the safety notes, not just the heater symbol.

It delivers about 25% less power, because output falls with the square of the voltage. A resistive element follows P = P_rated × (V_supply ÷ V_rated)², so a 240 V-rated 8 kW heater on 208 V produces about 6 kW. This catches out a lot of condo and light-commercial installs, where 208 V is the norm and the sauna simply never gets hot. The plan builder asks for your supply and derates automatically, and where a manufacturer publishes a separate 208 V volume range — HUUM does — it uses that table instead of the formula.

Six air changes per hour, or room volume divided by ten expressed in CFM. A 245 ft³ room therefore wants about 25 CFM. Placement matters as much as volume: intake low, around 6" above the floor near or under the heater so incoming air is heated immediately, and exhaust on the diagonally opposite wall so the air sweeps across the room rather than short-circuiting. There are two schools on the exhaust: a mechanical or "downdraft" layout puts it high and pulls air through, while the traditional Finnish convection layout puts a low exhaust under the far bench plus a separate high vent opened only to dry the room after use. Either works if the intake is low by the heater and the exhaust is diagonally opposite — a sauna with no ventilation is not just stuffy, it is a moisture problem in the walls.

Use the clearance in your specific heater's manual — there is no universal figure, and the range is enormous. A Harvia 8 kW wall unit needs about 3" (75 mm) to side walls and 43.3" (1100 mm) to the ceiling. A HUUM DROP needs 5.9" (150 mm) to a side wall. A Harvia Virta Pro needs 80 mm on every horizontal face and 1200 mm to the ceiling. A wood stove needs 19.7" or, unlisted, 48". Benches and guards count as combustible material for this purpose, which is why so many otherwise-good layouts fail — the bench is legal against the wall and illegal 30" from the stove. The plan builder draws the manufacturer's keep-out zone as a dashed footprint and turns it red the moment a bench, door swing or wall intrudes.

Near the door, on the wall you enter beside — not under the upper bench and not opposite the door. Two reasons. Cold air falling in through an opening door should meet the heater first, and the low intake vent sits near the heater for the same reason. And the heater is the one object in the room you never want to walk into, so it belongs where people are entering and standing, not where they are climbing. Its clearance zone will also eat bench run wherever you put it, which is exactly the trade-off the plan drawing makes visible.

Yes — about 30% more, because barrel and log rooms are effectively uninsulated. The staves are solid wood with no insulation cavity, so heat leaves through the shell continuously. The plan builder applies a 1.3× multiplier to uninsulated construction, which is often the difference between a 6 kW and an 8 kW heater. Barrels also lose usable bench depth at the curved ends, so a barrel seats fewer people than its footprint suggests.

Usually yes for the electrical work, and often yes for the structure if it is a new outbuilding. Requirements are entirely local, but the near-universal one is that a dedicated 240 V sauna circuit is permitted, inspected electrical work in both Canada and the US. Indoor conversions of an existing room are frequently simpler than a new outdoor build, which may pull in setbacks, foundations and, with a wood stove, a chimney inspection. The drawing this tool produces is a planning drawing that will help you have the conversation — it is explicitly not a stamped or engineered drawing, and no permit office will accept it as one.

No — and any tool that tells you otherwise is selling you something. The plan builder applies published manufacturer clearances, the NEC/CEC 125% continuous-load rule, and accepted Finnish ergonomic practice, so the drawing is right in the way a competent designer's sketch is right. It has not been reviewed by an architect, engineer or electrician, and it does not know your local amendments, your snow load, your setbacks or your panel. Use it to get the layout right and to arrive at your electrician and inspector with real numbers instead of a rough idea.

Cost is driven by four things: room size, wall assembly, glass, and heater class. Glass is the big one — a full glass front can cost more than the framing and cladding behind it, and it pushes you up a heater size at the same time. After that: cedar species and grade, whether the room is a conversion or a new structure, bench complexity, and whether the heater is a residential unit or a commercial one on three-phase. The honest answer is that a 5' × 7' insulated conversion and an 8' × 8' glass-fronted room are different projects by a multiple, not a percentage. Design the room first, then send us the drawing and we will price the real thing.

Yes. The builder draws rooms up to 1,000 square feet and banks multiple heaters automatically. Past about 12 kW you are in commercial territory, where the answers change: 208 V three-phase supply, multiple units rather than one large one, higher throughput ventilation, and bench layouts designed around turnover rather than one household. A 14' × 20' room seats roughly thirty. Above 1,000 ft² the right answer stops being a web form and becomes a site visit — talk to us and we will draw it properly.

The room geometry barely changes; everything around it does. Bench ergonomics, head zone, heater sizing and clearances are identical indoors and out. What changes is the shell — an outdoor room in a cold climate wants a genuinely insulated assembly, because the 30% uninsulated penalty is a year-round operating cost, not a one-off. Outdoor builds also add drainage, a frost-stable base, and often a permit path the indoor conversion avoids. Draw the interior here, and bring the site to the conversation.

Yes. Designing, redrawing and sharing a plan is free and unlimited, with no account. You can change dimensions as many times as you like and copy a link that reopens the exact design on anyone else's screen. The downloadable PDF and PNG are the one gated step: they ask a short set of questions about your project first, and unlock immediately after — no waiting on an email.

Yes, and that is what it is for. It is dimensioned in real inches at a real scale, so a carpenter can frame from it and an electrician can see the load, the circuit count and where the heater lands before quoting. What it is not is a stamped drawing — if your build needs engineered drawings for permit, this is the document you hand to the person producing them, which is a much shorter conversation than starting from a description.

A print-ready sheet at ½" = 1'-0" containing a floor plan and a section drawing, fully dimensioned. That includes wall thickness and interior clear dimensions, the bench layout with tier heights and depths, the heater with its manufacturer clearance zone drawn as a keep-out, the door and its swing, vent positions and sizes, the head-zone dimension, and a data block with heater model and kW, circuit and breaker sizing, seat count, room volume and required CFM. It carries the disclaimer that it is a planning drawing, because it is one.