Heater kW, stone charge, T&G paneling, benches and cost for a home sauna.
Estimates are planning aids, not a professional quote. Double-check quantities and product coverage — and any local code or permit requirements — before you buy.
⚠ The heater needs a dedicated 40A 240V circuit with GFCI protection — most jurisdictions require it on a wet-location appliance like a sauna heater. Have a licensed electrician size and permit the run; the gauge and breaker above are a planning estimate, not a substitute for their calculation.
⚠ The foil vapor barrier goes on the warm, interior side of the wall — under the paneling, facing into the room — which is the reverse of the poly barrier used on a standard exterior wall. Installing it on the wrong side traps moisture in the wall cavity instead of reflecting heat back into the room.
| Lumber & Decking | $1,508–$2,040 |
| HVAC | $479–$647 |
| Doors & Windows | $357–$483 |
| Flooring | $306–$414 |
| Fasteners & Hardware | $66–$90 |
| Membrane & Fabric | $55–$75 |
| Electrical | $52–$71 |
| Total | $2,823–$3,820 |
Excludes tools, delivery, tax and permit fees. Labor not included — this is a DIY materials estimate.
These are affiliate links: we may earn a commission if you buy through them, at no extra cost to you. It never changes what the calculator recommends — the shopping list comes from your dimensions, not from what pays.
About this calculator
Enter your sauna room's length, width and ceiling height, and the Sauna Calculator works out the heater size in kilowatts from the actual room volume — with a penalty added for any glass door or window, since bare glass loses heat much faster than a foil-backed wood wall. It rounds that to a standard heater tier, sizes the stone charge to match, and prices the electrical circuit or wood-stove option you pick.
From there it builds the interior fit-out: foil vapor barrier and furring for the wall assembly, cedar or hemlock tongue-and-groove paneling for the walls and ceiling, bench framing and slats at one or two tiers, a duckboard floor, and the door — all as a shopping list with a cost estimate, not just a coverage number. Switch between an electric heater on its own dedicated circuit and a wood-fired stove to see how the heater line, the stone charge and the warnings all change with it.
Step by step
A step-by-step walkthrough to go with your plan above. Follow the product instructions and any local code or permit requirements as you work.
Measure the finished room's length, width and ceiling height and use the calculator to size the heater in kW and the matching stone charge. Confirm the exact model's room-size chart before buying — stone tray capacity varies between manufacturers even at the same kW rating.
For an electric heater, have a licensed electrician run the dedicated 240V GFCI-protected circuit before you close in any walls. For a wood-fired stove, plan the chimney route and clearances first, since it can constrain where the stove itself can sit.
Cover every wall and the ceiling with foil-faced vapor barrier, shiny side facing into the room, overlapping and taping every seam. This goes on the warm interior side — the opposite of a standard exterior wall.
Install horizontal furring strips at 16 in centers over the foil on every wall. This creates the air gap the paneling needs and gives you a real nailing base instead of stapling boards straight to a stud through the foil.
Nail the tongue-and-groove boards to the furring, working ceiling first, then walls, leaving a small gap at the floor and any hot surfaces for wood movement. Let the boards acclimate in the room for a few days before installing.
Frame the bench structure at 16 in on center, bolted or lag-screwed to the wall framing (through the paneling into real backing, not just the furring), then lay the slats with a gap between each for airflow and drainage.
Set the interlocking duckboard tiles across the floor so bathers stand above standing water and the floor can air-dry between sessions.
Install the pre-hung door, load the stone tray, and run the heater through its first burn-off cycle with the door open to clear any manufacturing residue before the first real session.
Equip the job
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Keep planning
Interior & Finishing
Answers
A common planning rule is about 1 kW of heater output per 48 cubic feet of room volume for a foil-backed, all-wood interior, with extra kW added for any glass door or window since bare glass loses heat much faster than an insulated wall. A typical 6×6 ft sauna with a 7 ft ceiling works out to roughly 6 kW. This calculator runs that math from your exact room dimensions and rounds up to the nearest standard heater size so you're buying a unit that's actually sold, not a fractional number.
Stone charge scales with heater output — this calculator uses roughly 40 pounds of stone per kilowatt of heater capacity, sold in standard 44-pound bags. A 6 kW heater takes about 240 pounds, or roughly 6 bags. Always use stones sold specifically for sauna heaters rather than ordinary landscaping or river rock — the wrong stone can crack or fracture from the rapid heating and water-shock cycle and send hot fragments flying.
A sauna is the one wall assembly in the house where the vapor barrier faces the room instead of the exterior, because the interior is the hot, humid side and the goal is reflecting radiant heat back in rather than blocking moisture from outside. Foil, not poly sheeting, is used because it reflects infrared heat as well as stopping vapor. It's stapled directly to the framing, then furring strips go over it to create an air gap before the tongue-and-groove paneling is nailed on.
An electric heater is the simpler DIY path for an indoor sauna — it just needs a dedicated 240V circuit and heats up in about 30–45 minutes with a thermostat holding the temperature steady. A wood-fired stove gives the classic outdoor or off-grid sauna experience and doesn't depend on the electrical panel, but it needs the same class of insulated chimney, roof or wall penetration, and clearance-to-combustibles planning as a wood stove, which is a separate project on its own.
For a small 6×6 ft interior sauna fit into an existing framed room, materials commonly run $2,500–4,500 — the heater and paneling are the two biggest line items, followed by the bench lumber and the door. Larger rooms, a wood-fired stove with its separate chimney, or upgrading from hemlock to cedar throughout all push the total up. This estimate covers the interior fit-out only; framing a brand-new room or running new electrical service to the space are priced separately.
Cedar is the classic sauna wood — naturally rot- and insect-resistant, low in resin so it stays comfortable to touch at high heat, and it carries the aromatic scent most people associate with a sauna. Hemlock costs noticeably less, is nearly scent-free (a plus for anyone sensitive to cedar's aroma), and performs almost as well thermally, but it isn't as naturally decay-resistant if the room ever sees standing water. Either works structurally; the choice comes down to budget and scent preference.