Methodology & Assumptions
Every calculator here uses a published, industry-standard basis. We show the math so you can check it, and hand it to your electrician or builder.
Heater sizing
Base requirement = room volume (L×W×H) ÷ 45 cubic feet per kW, deliberately more conservative than the common ÷50. Corrections add to the effective volume: glass +1.2 cf per sq ft; cold surfaces (tile/concrete/stone) +25% of their area; uninsulated exterior wall +15% of volume; ceiling over 7 ft +10% per foot; outdoor +20% of the total. Result is rounded up to the nearest heater size sold.
Electrical circuit
Amps = watts ÷ volts. A sauna heater is a continuous load, so NEC requires the breaker ≥ 125% of the load current, rounded up to a standard size (NEC 240.6). Wire is the smallest 75°C copper conductor (NEC 310.16 ampacity) that carries the breaker, then upsized until single-phase voltage drop over your one-way run is ≤ 3% (Vdrop = 2 × 12.9 × I × L ÷ circular mils). Aluminium, 60°C terminations and local amendments change this, a licensed electrician has the final say.
Chiller sizing
Heat load = gallons × 8.33 × ΔT ÷ pull-down hours (water is 8.33 lb/gal, 1 BTU/lb·°F). Corrections: no insulation ×1.5, no cover ×1.2, outdoor hot summer ×1.25. HP ≈ BTU/hr ÷ 10,000 (1 HP ≈ 9,000–12,000 BTU/hr). Running cost assumes compressor input ≈ HP × 0.746 kW ÷ COP 3.
Running cost
Monthly kWh = kW × (heat-up + session hours) × sessions/week × 4.33 weeks. This is an upper bound: once up to temperature the element cycles at roughly 50–70% duty, so real bills run lower.
Room planner
Upper bench set so the top of the head clears the hot zone (about 36–42" below the ceiling), lower bench ~18", 20" bench depth, 24" door. Ventilation runs low intake by the heater to low exhaust on the opposite wall to drive convection.
Specs & sources
Every heater and chiller spec comes from the manufacturer manual or spec sheet, the source is linked on each heater and chiller record. Where a value is unpublished we leave it blank rather than estimate.
Prices
Prices are fetched from Amazon on a schedule (no more than once every 24 hours) and shown with the time they were fetched, the price at checkout is the one that applies. Each listing is re-verified against the model name so a relisted ASIN can never show the wrong price. As an Amazon Associate we earn from qualifying purchases. Prices and availability are pulled from Amazon on a schedule and shown with the time they were fetched; the price at checkout is the one that applies.