Sauna Wars' Missing Software Layer ($3.6M ARR)

The Heat Stack

Build the operating system for the new social bathhouse

The sauna is quietly becoming a third place.

Forget the lonely cedar box in the corner of a gym, or the resort spa you visit twice a year. A new wave of urban operators is building social-thermal venues around saunas, cold plunges, guided rituals, music, recovery, and community. Some sessions feel like meditation, some like a sober nightclub, some run like a fitness class. What operators sell now isn't access to a sauna. It's a programmed experience.

The money agrees. In May 2025, New York's Bathhouse raised $35 million from Imaginary Ventures — the firm behind Skims and Daily Harvest — to expand from three locations toward ten nationwide, starting with Los Angeles and continuing through Chicago, Nashville, and Philadelphia. Othership now runs four guided sauna-and-ice-bath venues across Toronto and New York. Lore Bathing Club opened a 6,200-square-foot Nordic club in NoHo, packaging Finnish sauna, infrared, and cold plunge into bookable 75-minute sessions. Sauna House is spreading "Thermal Cycles" across five Southern states. The trade press now calls it the "sauna wars."

The tailwind underneath all of it is real. The Global Wellness Institute pegs the global wellness economy at $6.8 trillion in 2024, with thermal and mineral springs alone generating roughly $72 billion across more than 31,000 establishments, and it forecasts double-digit annual growth for the category. Cold-water therapy has moved from a niche biohacker ritual toward something your neighbor does on a Tuesday.

So there's a startup opportunity here, and it isn't the obvious one. Don't open another bathhouse. That's a capital-intensive hospitality business with leases, construction risk, health-code exposure, and years of location-by-location grind. Build the software layer underneath the category instead.

Here's the opportunity:

The heist

The first-generation pitch sounds clean: Mindbody for sauna clubs.

It points in the right direction and stops short. Mindbody already sells booking, payments, staffing, and marketing software to wellness businesses, with US plans starting near $99 per month. Vagaro starts at $23.99. Momence handles classes, memberships, packs, email, SMS, and multi-location operations. Generic scheduling is a solved problem.

Sauna-specific software isn't an empty field either. Zipper runs a dedicated sauna and cold-plunge product with timed reservations, recurring memberships, session packs, waivers, and configurable terminology. Periode, out of Norway, layers in dynamic pricing, capacity control, gift cards, and smart-lock and sauna-oven integrations. Wunderbook and StudioDock cover simpler booking and private-suite models. The wood-grain landing page has been built several times over.

Which moves the opportunity somewhere else. The prize isn't another calendar. It's the thermal-operations layer for high-throughput, socially programmed venues: the software that lets operators run multiple rooms, multiple temperatures, multiple session formats, and multiple customer flows without turning the front desk into air-traffic control.

This is closer to an orchestration system for programmable heat than to spa-appointment software.

Why this category breaks the old software

Traditional spa software assumes a tidy unit of inventory: one practitioner, one room, one service, one customer, one start time, one end time.

A social bathhouse is messier. One guest reserves a 75-minute open flow and rotates between two saunas, an infrared room, three plunges, and a lounge. Another joins a host-led ritual with music and a fixed sequence. A third buys an off-peak membership and shows up four times a week. A fourth attends a ticketed Friday event with its own capacity, pricing, and staffing. Bathhouse's Brooklyn flagship alone juggles an event sauna near 175°F, a banya around 190°F, an infrared room, a 50°F plunge, a steam room, and a neutral pool, and the day pass invites guests to roam among all of it rather than consume one treatment.

Booking is the easy layer. The hard questions sit underneath it. How many people can enter at 6:00 p.m. without overloading the hottest sauna at 6:20? Should the venue sell another membership or protect peak inventory? Which formats actually drive repeat visits? What happens when a plunge goes offline mid-shift? This experience gets choreographed, not just scheduled, and nobody has built the software that does the choreographing.

The wedge: a thermal control board