Quick Answer: A 2025 University of Oregon study measured what actually happens inside your body during each — and a hot tub won on every measure the researchers took. In 20 healthy adults, 45 minutes in 104.9°F water raised core body temperature by about 1.1°C, versus 0.4°C for a traditional sauna and no change for far-infrared. The hot tub also raised cardiac output the most (+3.7 L/min), and it was the only session that triggered measurable immune-marker changes. Saunas still have real upkeep advantages (cheaper per session, no water chemistry), but if you’re choosing one for the physiological payoff, the water wins.
Last updated: October 31, 2026 — study figures re-checked against the published paper (American Journal of Physiology, July 2025), sauna costs updated to HomeGuide’s current ranges, per-session running costs recalculated at EIA’s August 2026 electricity price, and the Intex price re-checked on Intex’s store.
“Hot tub vs sauna” usually gets answered with vague wellness-blog claims about both being “great for relaxation.” That’s true but unhelpful when you’re deciding where a few thousand dollars of backyard budget actually goes. In 2025, researchers finally measured the two side by side in the same study — and the numbers aren’t close.
Hot tub vs sauna by the numbers
- +1.1°C vs +0.4°C vs +0.0°C — the core body temperature increase measured in hot water immersion, a traditional dry sauna, and a far-infrared sauna, respectively, in a 2025 study from the University of Oregon’s Department of Human Physiology (Atencio et al., American Journal of Physiology, July 2025).
- +3.7 vs +2.3 vs +1.6 L/min — the rise in cardiac output (blood pumped per minute) in the same three sessions, per the same paper.
- About 24x — water’s thermal conductivity relative to air (roughly 0.6 vs 0.026 W/m·K, standard physics figures, not a finding of the study), which is the physical reason immersion heats the body faster than sitting in hot air even at a much lower air/water temperature.
- 150-195°F is a traditional sauna’s typical air temperature and 120-140°F an infrared sauna’s, per HomeGuide, versus 100-104°F for a hot tub’s water — the sauna runs far hotter, but transfers heat into the body far more slowly.
- $2,300-$10,500 is HomeGuide’s installed range for an indoor prefab sauna room ($5,500-$14,500 outdoor prefab), versus $729.99 for the cheapest PureSpa inflatable on Intex’s own store on October 31, 2026.
Head-to-head comparison
| Factor | Hot Tub | Sauna |
|---|---|---|
| How it heats you | Water immersion (100-104°F) | Hot air or infrared light (150-195°F air, or cooler infrared) |
| Core temp rise (2025 Oregon study) | +1.1°C | +0.4°C (traditional) / +0.0°C (far-infrared) |
| Cardiac output rise (same study) | +3.7 L/min | +2.3 L/min (traditional) / +1.6 L/min (far-infrared) |
| Immune-marker response (same study) | IL-6 up after the session; NK cells up at 24 h; CD8+ T cells up at 24 and 48 h | No measurable response in either sauna |
| Typical upfront cost | From $729.99 (Intex's cheapest PureSpa, Intex store, Oct 31, 2026) | $200-$2,600 portable infrared; $2,300-$10,500 installed indoor room (HomeGuide) |
| Running cost | About $30-$60 a month in electricity, unlimited soaks | About $0.27 or less per infrared session; $0.73-$1.96 per traditional session (our math, 18.16¢/kWh) |
| Water chemistry / upkeep | Yes — sanitizer, pH, filters | No water to maintain |
| Muscle/joint therapy | Jets + buoyancy | Heat only, no massage action |
| Setup | GFCI outlet, most inflatable and plug-and-play models | Traditional: dedicated 220V circuit ($250-$900 to install, per HomeGuide); most infrared: standard 110V outlet |
Why the hot tub wins the physiology test
Water conducts heat roughly 24 times more efficiently than air. Sit in a 175°F sauna and the surrounding air is scorching, but air is a poor heat conductor and your body sheds heat by sweating into it. Submerge in 102°F water and you can’t sweat your way out — the water pulls heat into your body continuously, which is why the Oregon researchers found hot water immersion pushed core temperature up nearly three times as much as a traditional sauna, and roughly infinitely more than the far-infrared session, which barely moved the needle. That larger core-temperature swing is also what drove the bigger cardiovascular response (higher heart rate, sharper blood-flow increase, higher cardiac output) and the only measurable immune-marker shift (a rise in IL-6 followed by elevated immune cell counts 24-48 hours later) in the study.
None of that means a sauna is worthless — dry heat still raises heart rate and circulation and plenty of people find it more comfortable to sit in for longer stretches without the water-immersion effect on blood pressure that some cardiac patients need to watch. It means that if your goal is the specific physiological response researchers can actually measure, water immersion currently has the stronger evidence behind it.
What the Oregon study tested (and what it didn’t)
The paper is Atencio et al., “Comparison of thermoregulatory, cardiovascular, and immune responses to different passive heat therapy modalities,” American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, July 2025. Each of the 20 volunteers did all three sessions, at least a week apart:
| Session | Protocol | Core temp change | Cardiac output change | Immune response |
|---|---|---|---|---|
| Hot water immersion | 45 min at 40.5°C (104.9°F) | +1.1°C | +3.7 L/min | IL-6, NK cells and CD8+ T cells up |
| Traditional sauna | 3 x 10 min at 80°C (176°F) | +0.4°C | +2.3 L/min | None measured |
| Far-infrared sauna | 45 min at 45-65°C (113-149°F) | +0.0°C | +1.6 L/min | None measured |
Three limits matter before you apply this to your backyard. First, the volunteers were young and healthy (10 women, 10 men, average age 24), so the results don’t tell you how older adults or people with heart conditions respond. Second, it measured single sessions, not months of regular use. Third, the hot tub ran at 104.9°F for 45 minutes, slightly above the 104°F maximum the U.S. Consumer Product Safety Commission recommends and above what most inflatable tubs can reach; see our hot tub temperature guide for safe settings and soak times. A home soak at 102-104°F will likely raise core temperature less than the study’s session did.
Who should get a hot tub
Intex PureSpa Greywood Deluxe, 4-person (inflatable, budget entry point)
- Plugs into a standard household GFCI outlet — no dedicated room, no 220V circuit, no build-out.
- Delivers the stronger core-temperature and circulation response measured in the 2025 Oregon study, at a fraction of even an entry-level sauna's install cost.
- See our full best inflatable hot tub picks for sizes and price tiers.
Who should get a sauna instead
A sauna makes more sense if you specifically want dry heat with no water chemistry to manage, longer comfortable sessions than most people tolerate at 102°F, or a lower per-session running cost — an infrared session costs about $0.27 or less in electricity by our math, versus a hot tub’s continuous $30-$60/month draw. It’s also the better fit if you’re managing a condition where your doctor has flagged hot water immersion specifically (blood pressure, certain cardiac conditions) but hasn’t restricted dry heat exposure — that’s a conversation for your physician, not a blog post, but it’s a real reason some buyers choose sauna over tub.
The bottom line
If you’re picking one heat therapy purchase based on measurable physiological payoff, the 2025 University of Oregon research points at the hot tub: nearly triple the core-temperature rise of a traditional sauna, a stronger cardiovascular response, and the only measurable immune-marker change of the three heat types tested — all at a lower upfront cost (from $729.99 for an Intex PureSpa vs. $2,300 and up for an installed sauna room, per HomeGuide) than a home sauna install. A sauna still wins on cheaper per-session running cost and zero water maintenance, which is a legitimate reason to choose it or add it later as a second purchase. Start with our best inflatable hot tub roundup, or if cost is the deciding factor either way, see how much does a hot tub cost for the full price breakdown by tub type. Weighing other categories too? Our hot tub vs pool, hot tub vs swim spa, and hot tub vs jetted tub comparisons cover those buying decisions the same way.