The Infrared Sauna Glossary: 45 Terms, Plainly Defined

Heat & spectrum

Ten terms describing the heat itself — what infrared is, how it divides into bands, and how it is measured. Nearly every specification argument in this category is really an argument about wavelength. Deeper treatment: our near vs far vs full spectrum guide.

Emissivity

Emissivity is a number between 0 and 1 describing how efficiently a surface radiates heat compared with a perfect emitter at the same temperature. Sauna marketing converts it to a percentage, and heater panels are routinely advertised above 90%. The figure only means something when the brand also states the test method and the wavelength band it was measured across.

Far infrared (FIR)

Far infrared is the longest-wavelength infrared band, conventionally about 5.6 to 1,000 microns in sauna usage. It is what ordinary carbon and ceramic heaters emit, and it is absorbed at the skin surface, driving a heavy sweat response at comparatively low air temperatures. Nearly every sauna sold as "infrared" produces it; the difference between models is whether they produce anything else.

Full spectrum infrared

A full spectrum sauna emits near, mid and far infrared together, each band absorbed at a different depth. Genuine full spectrum requires dedicated hardware for the near and mid bands — a carbon panel labeled "full spectrum" with no named near or mid emitter is far infrared with a better adjective. The test: a full spectrum brand publishes the wavelength range for every band in writing.

Heat shock proteins (HSPs)

Heat shock proteins are molecules cells produce under thermal stress; their normal job is helping other proteins fold correctly and stay stable. They are the mechanism most often invoked to explain sauna effects, but the human sauna evidence is observational: the Kuopio cohort of 2,315 Finnish men found frequent sauna use associated with lower cardiovascular and all-cause mortality over about 20 years (Laukkanen et al., 2015) — an association, not a demonstrated pathway. See our heat shock protein guide.

Heat-up time

Heat-up time is how long a cabin takes to reach target temperature from a cold start. Infrared cabins typically publish 20 to 45 minutes, far shorter than a traditional stove sauna that must bring a whole room of air to roughly 175°F. Ambient temperature matters — an outdoor cabin on a 20°F morning takes materially longer — so a published figure without a starting condition is not a number.

Löyly

Löyly is the Finnish word for the burst of steam that rises when water is ladled onto hot sauna stones, and by extension for the quality of that heat. It is the defining feature of traditional Finnish bathing. Infrared saunas have no stones and no water, so they produce no löyly at all — if löyly is what you want, buy a traditional sauna.

Micron (µm)

A micron, or micrometer, is one millionth of a meter and the unit used for infrared heat wavelengths; one micron equals 1,000 nanometers. That is why heat specs are quoted in microns and light-therapy specs in nanometers — same quantity, different convenient scale. Far infrared sits around 5.6 to 1,000 microns, mid around 1.4 to 5.6, near around 0.78 to 1.4.

Mid infrared (MIR)

Mid infrared occupies the band between near and far, conventionally about 1.4 to 5.6 microns in sauna usage. It penetrates further than far infrared and is generally associated with warming soft tissue rather than just the skin surface. Producing it requires a dedicated emitter, which standard carbon panels do not have.

Near infrared (NIR)

Near infrared is the shortest infrared band, roughly 0.78 to 1.4 microns (780 to 1,400 nanometers), sitting immediately beyond visible red light. In a sauna it comes from a dedicated emitter or from LED hardware, never as a by-product of a far-infrared carbon panel. It is also the band that overlaps red light therapy — see near-infrared light for the therapy side.

Wavelength

Wavelength is the distance between successive peaks of an electromagnetic wave, and it determines how deeply energy is absorbed and by which molecules. It is the most useful number in this category because it cannot be fudged by adjectives: "deep penetrating" means nothing, "830nm" means something. Heat wavelengths are quoted in microns, light-therapy wavelengths in nanometers.

Light therapy

Seven terms covering the light side of a modern cabin, where the marketing is loosest and the specification gap is widest. The distinction between decorative colored lighting and dosed therapeutic light is the most consequential thing on this page. More: our red light therapy in saunas guide and the 2026 red light sauna rankings.

Chromotherapy

Chromotherapy, or color light therapy, is a colored LED system that cycles through hues to influence mood and atmosphere. It is ambient lighting: low-power LEDs, wavelengths typically unpublished, no irradiance figure offered because a decorative fixture does not need one. Chromotherapy is not red light therapy — a listing reading "chromotherapy with red light" is describing a mood light, not a dose. The test is data: therapeutic light comes with named wavelengths and irradiance at a stated distance; chromotherapy comes with a color wheel. Full explainer: chromotherapy versus therapeutic light.

Dual-chip LED

A dual-chip LED houses two emitter dies in one package, so a single diode outputs two wavelengths — typically one red and one near-infrared. The practical benefit is density: more wavelengths and more output per square inch of panel. Peak's panel uses 216 dual-chip LEDs per panel in a 9-inch by 36-inch panel. Diode count alone proves nothing without published wavelengths and irradiance.

Irradiance (mW/cm²)

Irradiance is the light power landing on a surface, measured in milliwatts per square centimeter — the dose figure for red light therapy, equivalent to asking how many milligrams are in a pill. It falls off sharply with distance, so a number quoted without a distance is meaningless. Peak publishes 175 mW/cm² at 6 inches, 107 at 12 inches and 80 at 24 inches; most sauna brands publish no per-distance irradiance at all.

Nanometer (nm)

A nanometer is one billionth of a meter, the unit for light-therapy wavelengths. Visible red runs roughly 620 to 750nm and near-infrared roughly 750 to 1,400nm, so a red light device is specified by the exact wavelengths it emits — 660nm and 850nm are the most commonly published in the category. Peak's panel emits 8 wavelengths (630–1060nm).

Near-infrared light (in red light therapy)

In a light-therapy context, near-infrared light means the invisible 750-to-1,400nm wavelengths delivered by LEDs rather than by a heat emitter. Because it is invisible, a panel can look dim while running significant near-infrared output. Peak covers it with 810, 830, 850 and 1060nm alongside red at 630, 650, 660 and 670nm — 8 wavelengths (630–1060nm) in total — and it is dosed by irradiance and time exactly like visible red.

Photobiomodulation (PBM)

Photobiomodulation is the scientific name for red light therapy: red and near-infrared light at non-thermal doses producing a biological response in tissue, historically also called low-level laser therapy. It is the term used in the research literature rather than in advertising; the standard overview is Hamblin, 2017. It is dose-dependent — wavelength, irradiance and exposure time all matter, and more is not automatically better.

Red light therapy (RLT)

Red light therapy is the consumer name for photobiomodulation: specific red and near-infrared wavelengths at a measured irradiance, for a defined time, at a defined distance. The most studied application is skin, reviewed in Avci et al., 2013. In saunas it is usually an add-on — several premium brands sell a light tower or panel as a four-figure accessory. Peak includes an 8-wavelength (630–1060nm) panel standard on every full-spectrum model.

Construction & materials

Seven terms about what the cabin is made of and what generates its heat. Wood species is the decision buyers agonize over most and it matters least; heater type and joinery matter more. Our hemlock vs cedar comparison settles the wood question with numbers.

Carbon heater

A carbon heater is a large, flat far-infrared panel that heats a wide area at a moderate surface temperature, giving even wraparound coverage. It is the dominant heater type in home infrared saunas because the panels are broad, quiet and comfortable to sit near. Its limitation is spectral: carbon emits far infrared only, so a carbon-only cabin is not full spectrum however it is marketed.

Cedar (Western red cedar)

Cedar is the aromatic, naturally moisture-resistant softwood traditionally used in sauna construction, prized for its scent and warm reddish grain. It carries a real premium — visible in Peak's own lineup, where the cedar Rainier is $7,250 against the hemlock Shasta at $6,950. Functionally it does not heat better or last meaningfully longer than hemlock; buy cedar for the scent and the look, which is the honest reason to pay for it.

Ceramic heater

A ceramic heater is a rod-style far-infrared emitter running at a much higher surface temperature than a carbon panel, producing intense heat concentrated in a smaller zone. It heats fast and feels strong at close range, but coverage is uneven, so cabins using it need more emitters placed carefully. Carbon versus ceramic is a genuine design trade-off, not a right answer.

Hemlock (Canadian hemlock)

Hemlock is a stable, pale, nearly scent-free softwood widely used in infrared cabins and the sensible default for anyone sensitive to fragrance. It is dimensionally stable under repeated heat cycling and costs less than cedar — the hemlock Shasta is $6,950 and Everest $7,950 in Peak's range. It is not a downgrade: build quality, kiln drying and joinery affect longevity far more than species does.

Kiln-dried lumber

Kiln-dried lumber has had its moisture content reduced in a controlled kiln before milling, typically to single-digit percentages, rather than being air-dried. This matters enormously in a sauna, because wood still holding moisture warps, cups and cracks when cycled through repeated heating. It is the boring construction detail that decides whether a cabin still closes properly in year five.

Tempered glass

Tempered glass is heat-treated safety glass, several times stronger than ordinary annealed glass, that crumbles into blunt granules instead of shards if it breaks. It is the standard for sauna doors and windows for that reason, and it tolerates the daily thermal cycling a sauna door endures. Bronze or grey tinting is cosmetic and does not change the safety rating.

Tongue-and-groove

Tongue-and-groove is joinery where each board's protruding tongue seats into the next board's groove, locking panels together without visible fasteners. In a sauna it does two jobs: sealing the wall against heat loss, and letting wood expand and contract through heating cycles without gapping. If a cabin's walls are tongue-and-groove and the lumber is kiln-dried, the shell is built properly.

Electrical

Eight terms that decide whether your sauna plugs in or needs an electrician — the most common source of unpleasant surprises after delivery. Sort this out before you fall in love with a model. Full detail: our sauna electrical requirements guide.

120V/15A circuit

A 120V/15A circuit is the standard household outlet found throughout most American homes, and the friendliest answer to "what does this sauna need" — it plugs into a normal wall outlet with no electrician. Its ceiling is 1,800 watts, which in practice limits it to one-person cabins; Peak's Shasta ($6,950) and Rainier ($7,250) both run on 120V/15A. If you rent, or you do not want to touch your panel, shop this category.

120V/20A circuit

A 120V/20A circuit is still standard household voltage but rated for higher current, giving a 2,400-watt ceiling instead of 1,800. Many homes already have 20A circuits in kitchens, garages and laundry areas; you verify by reading the number stamped on the breaker, not by looking at the outlet. Two-person cabins commonly need one — Peak's Everest ($7,950) and Fuji ($8,250) are both 120V/20A.

240V circuit

A 240V circuit is a dedicated high-voltage line of the type used for an electric dryer or range, installed by a licensed electrician. Larger cabins and all outdoor models generally need one: Peak's Denali ($9,750), Matterhorn ($10,750) and outdoor Patagonia ($10,750) run on 240V/20A, while the outdoor Kilimanjaro ($13,450) and El Capitan ($16,750) need 240V/30A. Budget for the electrician alongside the sauna — the run length from your panel drives that cost more than anything else.

Amperage (amps)

Amperage is the rate of electrical current a circuit can safely carry; combined with voltage it sets the maximum power a sauna can draw, since volts multiplied by amps equals watts. That arithmetic is the most useful thing a shopper can know: a 120V/15A sauna cannot draw more than 1,800 watts, whatever a listing implies. Amperage is what the breaker is rated for, and it is printed on the breaker switch.

Dedicated circuit

A dedicated circuit serves a single appliance and nothing else, running from its own breaker in the panel. Saunas want one because a heater drawing near the circuit's ceiling will trip the breaker the moment a vacuum or garage freezer starts on the same line. "Plug-and-play" and "dedicated circuit" are not in conflict — a plug-in sauna can and should have the outlet to itself.

GFCI (ground-fault circuit interrupter)

A GFCI is a fast-acting safety device that cuts power within milliseconds when it detects current leaking to ground, the condition that causes electrocution. Electrical code generally requires GFCI protection on outdoor, garage and damp-location circuits, which covers most outdoor sauna installations. Protection can live in the breaker, the outlet, or the appliance's own cord — ask which applies to your model, because it changes what your electrician installs.

Hardwire vs plug-in

A plug-in sauna terminates in a standard cord and plug; a hardwired sauna is wired permanently into a junction box by an electrician, with no plug involved. Plug-in is the friction-free path: no electrician, no inspection in most jurisdictions, and the unit moves with you. The practical rule is that 120V models plug in, while 240V models are hardwired or use a dedicated high-voltage outlet.

Kilowatt-hour (kWh)

A kilowatt-hour is 1,000 watts drawn for one hour — the unit your utility bills you in. It lets you compute worst-case running cost in one line: a 120V/15A cabin draws at most 1,800 watts, so a full hour at maximum is 1.8 kWh, roughly $0.31 at the approximately $0.17 per kWh U.S. average residential rate. Real sessions cost less because heaters cycle off; our electricity cost guide works the math per model.

Buying & ownership

Seven terms from the purchase and ownership side, where the language is deliberately soft and the fine print does the real work. Two of them — limited lifetime warranty and duty cycle — hide more money than anything else on this page.

Curbside freight delivery

Curbside freight means the carrier delivers your crated sauna on a freight truck and leaves it at the curb or the end of your driveway; moving it from there is your responsibility. It is the default service level across the industry, because cabins ship as crated pallets weighing several hundred pounds. Plan for two or more people and a route wide enough for the crate. Peak includes free shipping on every model — confirm the service level for your address at checkout.

Duty cycle

Duty cycle is the proportion of time a sauna's heaters actually run versus cycle off at temperature, and by extension how much continuous use a cabin is designed to handle. It is a residential curiosity and a commercial necessity: a home cabin used once a day is nothing like a gym cabin running back-to-back sessions for fifteen hours. If you are buying for a business, ask for the duty cycle rating in writing and confirm the warranty covers commercial use.

ETL certification

ETL is a product safety certification mark issued by Intertek, a nationally recognized testing laboratory, confirming a product was tested against the applicable North American safety standard. It is functionally equivalent to a UL listing — different lab, same recognized status — and it is what an inspector or insurer looks for. Certification applies to specific models, not to brands, so check the listing mark on the product page of the exact model you are buying.

HSA/FSA eligibility

Health Savings Account and Flexible Spending Account funds are pre-tax dollars for qualifying medical expenses, and wellness equipment can sometimes qualify when a licensed provider issues a Letter of Medical Necessity. Peak supports HSA and FSA payment through Truemed, which handles the qualification step at checkout. Eligibility depends on your circumstances and plan administrator — this is not tax or medical advice. See our HSA/FSA page.

Limited lifetime warranty

"Limited lifetime" sounds like forever and almost never means it: the home sauna convention treats a product's lifetime as about seven years, and several brands define it that way in their terms and conditions rather than in the headline. The word only becomes a defined term when the brand writes the number down — Peak publishes limited lifetime coverage on structure, wood and heating elements defined as 7 years residential, plus a 7-year red light panel warranty and lifetime U.S.-based support. The second question matters as much: parts coverage is not repair coverage, so ask who pays labor and freight on a claim in year two. An undefined "lifetime" is a marketing word; a defined one is a contract. Our 2026 warranty comparison reads every brand's terms side by side.

Lift-gate service

Lift-gate service is a freight add-on where the truck carries a powered platform that lowers the crated sauna from the trailer bed to ground level. Without it, a residential delivery can arrive with no safe way to get several hundred pounds down. It is usually a modest fee and the most commonly skipped delivery option buyers later wish they had bought — ask whether it is included before you finalize any sauna order.

White-glove delivery

White-glove delivery is the upgraded service where the crew brings the sauna inside and places it in the room you designate, sometimes unpacking and removing packaging; assembly is usually a separate service again, so read what is included. It typically costs several hundred dollars above freight and is quoted by the carrier, not the manufacturer. It earns its price for basements, upper floors and tight stairwells — assembly itself is generally a two-person job with hand tools (assembly walkthrough).

Practice

Six terms about actually using the thing. Protocols vary by person and goal, and nothing here is medical advice — the numbers are starting points, not prescriptions. Our temperature and duration guide goes deeper on session design.

Cold plunge

A cold plunge is deliberate immersion in cold water, typically 40°F to 55°F, for an exposure measured in minutes rather than tens of minutes. In sauna practice it is the cold half of contrast therapy, used after a heat round. Cold immersion produces a strong cardiovascular response, which is exactly why anyone with a heart condition should clear it with a physician first.

Contrast therapy

Contrast therapy alternates heat and cold within one session — classically a sauna round, then a cold plunge or cold shower, repeated two or three times. The traditional Nordic pattern is heat until thoroughly warm, cold for one to three minutes, then rest until breathing settles before the next round. Stop well short of shivering or dizziness; our contrast therapy guide lays out the full sequence.

Core body temperature

Core body temperature is your internal temperature, normally around 98.6°F, as distinct from skin temperature, which rises far faster and higher in a sauna. A session raises core temperature by roughly one to two degrees Fahrenheit — a small number that drives the whole response, including sweat rate and elevated heart rate. It is also why sauna use carries specific cautions during pregnancy and for cardiovascular conditions, and why perceived heat is a poor guide to dose.

Hydration and electrolytes

Sauna sessions produce meaningful fluid loss through sweat, along with sodium and other electrolytes, which makes hydration part of the protocol rather than an afterthought. The practical habit is drinking before the session as well as after, and replacing electrolytes when sessions are long, frequent or stacked with exercise. Lightheadedness on standing is the early sign you are under-hydrated or have stayed in too long; alcohol before or during a session compounds both risks.

Sauna session protocol

A session protocol is the defined combination of temperature, duration, frequency and recovery — the recipe rather than the equipment. A typical infrared starting point is 20 to 30 minutes at a comfortable temperature, extended gradually as you acclimate; Peak's outdoor models are rated to a published 170°F maximum for traditional-style heat outdoors. Every Peak sauna includes lifetime access to Peak Wellness Club — daily guided sessions and 30-day programs — which no other sauna brand includes.

Session frequency

Session frequency is how many times per week you use the sauna, and it is the variable the observational research keeps pointing at. In the Kuopio cohort, associations with lower cardiovascular and all-cause mortality were strongest at 4 to 7 sessions per week versus once weekly (Laukkanen et al., 2015), with a similar frequency pattern reported for dementia incidence (Laukkanen et al., 2017). These are associations in traditional Finnish saunas, not causal proof and not infrared trials. The buyer's takeaway is unglamorous: consistency beats intensity.

Where to go next

If you know the vocabulary and want the decisions, start with the ultimate sauna buying guide, which walks the five choices in order. For a model recommendation based on your space, budget and circuit, the sauna finder takes about a minute. And if what you came to settle was whether a cabin's red light is real therapy or a mood light, that comparison is here.

Peak Saunas products are wellness products, not medical devices. Nothing on this page is medical, tax or legal advice, and no statement here is intended to diagnose, treat, cure or prevent any disease. Research links describe what the cited studies report; most sauna research to date was conducted in traditional Finnish saunas and is observational. Consult a physician before beginning sauna use, particularly if you are pregnant or have a cardiovascular condition. Prices and specifications verified August 5, 2026 and subject to change.