Short answer
An independent lab, Surface Optics, measured Sun Home's infrared sauna heaters while running. Heater surfaces averaged 284°F on the standard single-bulb heater and 292°F on the low-EMF double-bulb heater (140.0°C and 144.3°C). In this test the low-EMF heater averaged slightly more heat, not less, and scored about 61 percent lower on a same-photo red-glow index. Full report below.
Read the full Surface Optics report (PDF, 15 pages), dated September 21, 2026. We paid for the study; the lab ran the test its own way and wrote up what it found. It measured one heater of each type, four times each. The headline comparison is on report page 1; the detailed results are on pages 7 and 8.
Three things the test showed
How hot do they get?
Hot. The heater surfaces averaged 284°F on the standard single-bulb heater and 292°F on the low-EMF double-bulb heater, with the hottest spots near 400°F. That is the heater face, not the cabin air; cabin temperatures are on each product page.
Does low EMF mean less heat?
Not in this test. Our low-EMF double-bulb heater ran slightly hotter than the standard heater and averaged slightly more heat from its surface, about 4 percent, a gap small enough to sit inside the test's run-to-run variation. Read it as comparable performance with the low-EMF heater a little higher, not as a large advantage.
Does a dimmer glow mean a weaker heater?
Not in this test. In one same-frame photo, the low-EMF heater's red-glow score was about 61 percent lower (0.39 against 1.00), and its surface still measured hotter. Bright red bulbs show you brightness, not heat.
Why this matters
Heat is what you are paying for
An infrared sauna is its heaters. The warmth you feel starts at the heater face: how much heat leaves that surface depends on how hot it runs, and the effect compounds as the temperature climbs. This test puts lab-measured numbers on it: heater surfaces averaging 284°F and 292°F, with hottest spots near 400°F, measured rather than claimed. How much of that heat reaches you depends on where you sit, which this test did not measure. But the heat has to leave the heater first, and this is the measurement of that.
Low EMF should not cost you warmth
Many people choose a low-EMF sauna for peace of mind and then wonder whether they gave up heat to get it. In this test they did not: the low-EMF heater ran slightly hotter and averaged slightly more heat than the standard one. Buying low EMF did not mean giving up heat at the heater face; the two heaters performed comparably, with the low-EMF one slightly higher on average.
A softer glow, not a weaker heater
Showrooms and product photos sell heaters by how red they look. This test shows why that is a poor guide: the low-EMF heater scored about 61 percent lower on the photo's red-glow index and measured hotter. Judge heaters by measured surface temperature and heat given off, which is what this page gives you, not by the glow.
Numbers you can compare
Every brand says "powerful heaters." A measured surface temperature, a heat figure in a real unit, a named lab and the full report let you compare saunas on evidence instead of adjectives. It also means we cannot round up, which is why we publish the parts that do not flatter us.
What it does not tell you
One heater of each type, four rounds, one sauna: enough to say the two heaters performed comparably at the heater face, with the low-EMF one slightly higher on average. How much heat reaches your skin depends on how far you sit from the heaters and how the cabin is built, and this test measured neither that nor the cabin air temperature. It did not measure EMF either; a separate Vitatech survey did. For cabin temperatures, use each product page; for comparing brands, use the five questions further down this page.
Why we measure instead of describe
Every infrared sauna brand says its heaters are powerful. Very few publish a measurement, fewer name the lab, and almost none post the report. We do all three. A sauna is a big purchase, and you should be able to check what we say instead of taking it on faith. So far that record includes an independent EMF survey by Vitatech, a cabin-air test by an accredited laboratory, a heater-surface study by Surface Optics, and now this running-heater test. Every document is on our safety and testing hub.
We paid for this study. That is how independent testing works: the maker supplies the hardware, the lab decides how to test it and writes up what it finds. We publish the report as the lab wrote it, including the numbers we would not have chosen to highlight and the limits the lab put on its own conclusions. Both are below.
The numbers at a glance
| Measurement | Single-bulb heater | Double-bulb heater |
|---|---|---|
| Directional thermal emittance, 20° (room temperature) | 0.978 ± 0.002 | 0.972 ± 0.001 |
| Effective emissivity in the thermal camera's band | 0.982 | 0.977 |
| Mean heater-face temperature | 140.0 ± 0.9°C (284°F) | 144.3 ± 3.8°C (292°F) |
| 95th-percentile heater-face temperature | 197.2 ± 2.3°C (387°F) | 203.0 ± 2.6°C (397°F) |
| Calculated surface-equivalent radiant exitance | 1.59 ± 0.02 kW/m² | 1.65 ± 0.06 kW/m² |
| Photographic red-incandescence index, same frame (single-bulb = 1.00) | 1.00 | 0.39 |
How the lab measured it
Our first Surface Optics study measured the optical properties of unpowered heater samples at room temperature and left the operating question open. This second study answers it with the heaters running, in four steps (report page 3).
- Room-temperature reflectance. The ET-100 infrared reflectometer measured each surface in six wavelength bands from 1.5 to 21 µm at 20° and 60° incidence, three repeats per surface, with the heater system passive. Reflectance converts to emittance (emittance equals one minus reflectance).
- Camera-band emissivity. The long-wave ET-100 data were weighted over the thermal camera's response band, giving effective emissivity values of 0.982 for the single-bulb felt face and 0.977 for the double-bulb felt face: measured inputs rather than generic handbook values (report page 6).
- Radiometric thermography. A radiometric FLIR long-wave infrared camera recorded the energized heaters. A radiometric camera measures infrared radiance, not temperature; each heater's radiance field was corrected with its own measured emissivity to produce a surface-temperature field.
- Calculated radiant exitance. The corrected temperature field was combined with temperature-dependent hemispherical emittance using the Stefan-Boltzmann relation to calculate surface-equivalent radiant exitance, the thermal power emitted per unit of heater-face area into the outward hemisphere, reported in kW/m².
All primary comparison measurements were taken during continuous heating, before the sauna reached its 170°F control set point, so both heaters were continuously energized throughout the analyzed sequence. Four matched single-bulb and double-bulb measurement pairs were acquired within approximately 7 to 9 seconds of one another, and the ± values on this page are the standard deviation across those four passes (report pages 7 and 15). Two rear-wall heaters were characterized: the left single-bulb heater and the adjacent center double-bulb heater. A third single-bulb heater appears in the visible photograph only as a same-exposure reference for the glow comparison (report page 5).
Results: heater-face temperature
In plain terms: the heater surfaces averaged 284°F and 292°F, with the low-EMF heater a few degrees hotter. The detail follows.
| Thermal metric | Single-bulb heater | Double-bulb heater | Double minus single |
|---|---|---|---|
| Mean heater-face temperature | 140.0 ± 0.9°C | 144.3 ± 3.8°C | +4.4°C |
| 95th-percentile temperature | 197.2 ± 2.3°C | 203.0 ± 2.6°C | +5.8°C |
| 99th-percentile temperature | 214.5 ± 0.9°C | 215.7 ± 0.3°C | +1.2°C |
The double-bulb heater was hotter in three of the four matched passes, and its upper-temperature distribution also shifted upward (report page 7). Both designs distribute thermal output over the full heater face; in the report's geometry-registered difference field, the double-bulb heater shows multiple regions that ran hotter than the corresponding regions of the single-bulb heater (report page 9).
These are surface temperatures of the heater face under an emissivity-corrected camera. They are not cabin air temperatures, which are published per model on each product page, and the report does not state the cabin temperature at the moment of each pass beyond the fact that it was below the 170°F set point.
Results: calculated radiant output
In plain terms: the low-EMF heater gave off about 4 percent more heat from its surface than the standard heater. That gap is real in this test but small, and it sits inside the run-to-run variation, so read it as comparable heat with a slightly higher average for the low-EMF heater, not as a lot more.
| Radiative metric | Single-bulb heater | Double-bulb heater | Difference |
|---|---|---|---|
| Calculated surface-equivalent radiant exitance | 1.59 ± 0.02 kW/m² | 1.65 ± 0.06 kW/m² | +3.7% |
| Relative heater-face result | 100% | 103.7% | +3.7 points |
Because the two heater faces have nearly the same emittance, the difference in calculated radiant exitance is driven by operating temperature rather than by the felt coating. For comparable active heater-face area, radiant exitance is directly proportional to the thermal power the observed front surface emits, which is why the report treats it as the physically meaningful basis for comparing the two architectures (report page 8).
For scale, 1.59 kW/m² is 1,590 watts per square meter of heater face. It is a calculated surface quantity and it describes the heater surface only. The infrared energy reaching a person on the bench depends on distance and viewing geometry, which this study did not measure.
Results: visible glow is not infrared output
In plain terms: the low-EMF heater looked dimmer and measured hotter. Glow tells you how bright the bulb is, not how much heat is coming off the face.
In a single visible photograph taken with common exposure and white balance, the report quantified the red glow of each heater with a photographic red-excess index, computed from the excess red-channel signal within equal-sized heater regions and normalized to the measured single-bulb heater: single-bulb 1.00, double-bulb 0.39, and the reference single-bulb heater 1.08 (report page 5). The index is not calibrated pyrometry or calibrated brightness; it is a relative indication of filament incandescence.
The result cuts against the most common shortcut in sauna shopping. For incandescent elements of comparable construction, a lower visible red signal is consistent with a lower filament temperature, yet the emissivity-corrected camera shows the double-bulb heater face slightly hotter. How brightly a heater glows is not a measure of the infrared output at its face. The report attributes the measured behavior to the two-element architecture distributing thermal loading across additional emitting-element area while maintaining a strong infrared thermal state at the heater face (report page 12).
The other heaters in the cabin
| Surface | Effective camera-band emissivity | Corrected active-region mean | 99th percentile |
|---|---|---|---|
| Full-spectrum front heater (glass) | 0.914 | 148.7°C (300°F) | 215°C |
| Floor heater (glass) | 0.944 | 55.7°C (132°F) | 65°C |
The front heater reached a corrected active-region mean of 148.7°C with a 99th-percentile temperature of approximately 215°C, a thermal state comparable to the bulb heaters. The floor heater, positioned under the feet, operated at a much lower thermal state during the test. Carbon far-infrared panels were not part of this study.
How to use this when you are comparing saunas
Treat heater claims the way we had ours treated: as something to check. Five questions for any brand, ours included:
- Has anyone measured how hot the heater surface actually runs, or is the brand only quoting an emissivity number?
- Is the heat given off reported in a real unit, such as watts per square meter, and for what size of heater?
- Who did the test, and can you read the whole report?
- If a heater is sold as low-EMF, was its heat output measured against the standard design, or just claimed?
- Are photos of glowing heaters being offered as proof of heat?
This page answers all five for the two heaters that were tested. If a brand cannot answer them for its own heaters, you are comparing adjectives.
What this test does and does not show
In plain terms: the test shows comparable heater-face performance from the two heaters, with the low-EMF heater a little hotter on average in this run. It does not measure EMF (a separate lab did that), it does not measure electrical efficiency, and it does not tell you how much heat reaches your skin on the bench. The detail follows.
We commissioned this study to answer a question buyers ask about low-EMF heater designs: does lowering EMF cost heat? In this comparison it did not. The double-bulb heater, which the report identifies as Sun Home's low-EMF design, matched the single-bulb heater's emittance to within a percentage point, ran slightly hotter at the face, and produced slightly higher calculated radiant exitance (report pages 1 and 12).
What that establishes has limits. The comparison involved one specimen of each design and four matched measurement pairs. The 3.7 percent exitance difference sits within the overlap of the two specimens' pass-to-pass variation (1.59 ± 0.02 against 1.65 ± 0.06 kW/m²), the double-bulb temperature mean carries a ± 3.8°C spread, and the double-bulb heater led in three of the four passes rather than all four. Overlapping variation does not establish a difference between the designs, and it does not establish equivalence either. What the data show is comparable observed performance in this setup, with the double-bulb specimen slightly higher on every reported metric.
This is not an EMF measurement. The study did not measure electromagnetic-field magnitude; our EMF record is the independent Vitatech survey summarized on our safety and testing hub and explained in how our EMF testing works. It is not a wall-plug efficiency figure: efficiency is an output-to-input ratio, and this study quantified the output side of the heater face only (report page 3). It does not establish the infrared dose reaching a person on the bench, and it does not map the tested heaters to specific production models, hardware editions or shipping dates.
Two smaller disclosures. The report gives the double-bulb heater's calculated hemispherical emittance at 300 K as 0.923 ± 0.002 in its main tables (pages 4 and 6); Appendix A (page 13) prints 0.922, which is within that uncertainty, and neither value changes the operating results on this page. The report also repeats the exterior solar-optical measurements of the aluminum wall and exterior glass (pages 10 and 11), which are covered on our heater emissivity testing page.
Bottom line
An independent lab ran our infrared heaters and measured them. The heater surfaces averaged 284°F on the standard heater and 292°F on the low-EMF heater (140.0°C and 144.3°C). In this test the low-EMF heater averaged slightly more heat from its surface (1.65 against 1.59 kW/m²) and scored about 61 percent lower on a same-photo red-glow index. One heater of each type, measured four times: enough to say the two heaters performed comparably at the heater face, with the low-EMF one slightly higher on average; not enough to call it a large advantage or to prove the two are identical. The full report is public, and the questions we asked of our own heaters are the ones to ask of any sauna you are considering.
- Explore full-spectrum infrared saunas
- Read the full Surface Optics report (PDF)
- Talk with an expert
- EMF, VOC and materials testing
Frequently asked questions
Are Sun Home's infrared heaters independently tested?
Yes. Surface Optics Corporation, an independent optical measurement lab in San Diego, measured one standard single-bulb heater and one low-EMF double-bulb heater while they were running, using a thermal camera calibrated to our heater material, and reported the results on September 21, 2026. Sun Home paid for the study; the lab controlled the method and wrote the report, which is published in full on this page.
How hot do Sun Home's infrared heaters get?
The heater surfaces averaged 284°F on the standard single-bulb heater and 292°F on the low-EMF double-bulb heater (140.0°C and 144.3°C), with the hottest 5 percent of each face above 387°F, measured across four matched passes on one heater of each type. These are heater-surface temperatures from a calibrated thermal camera, not cabin air temperatures; cabin temperatures are published per model on each product page.
Does the low-EMF heater give up heat?
Not in this test. The low-EMF double-bulb heater ran slightly hotter than the standard heater (144.3°C against 140.0°C) and averaged slightly more heat from its surface (1.65 against 1.59 kW/m², about 4 percent). The differences are small and sit inside the run-to-run variation, so the fair reading is that the two heaters performed comparably, with the low-EMF heater a little higher; the test does not prove a difference or prove they are identical. EMF itself was not measured in this study.
Does a heater that glows less put out less heat?
Not in this test. The low-EMF heater scored about 61 percent lower than the standard heater on a red-glow index taken from one same-frame photo (0.39 against 1.00), yet its surface ran 4.4°C hotter and averaged about 3.7 percent more heat. The glow index compares brightness in a photograph, not temperature, and how bright a bulb looks is not a measure of the heat coming off the heater face.
Why should I trust a test the brand paid for?
Because you can check it. The lab is named, the method is described step by step, the report is published as the lab wrote it, the numbers on this page are the ones the lab printed, and we disclose the parts that do not flatter us, including a small inconsistency inside the report. A paid test is only as good as its transparency, so we publish everything.
Was EMF measured in this study?
No. This study measured heat, not EMF. Our EMF numbers come from a separate independent survey by Vitatech, summarized on our safety and testing hub, and the report's conclusion about the low-EMF design reads its heat results alongside those separate EMF measurements.
Is this an efficiency measurement?
No. Efficiency compares heat out with electricity in, and this study measured only the heat side. An efficiency percentage would also need the electrical input measured at the same time and the total heat output measured at a set distance.
How many heaters were measured, and how many times?
Two heaters, four times each: one standard single-bulb heater and one low-EMF double-bulb heater on the rear wall of the tested sauna, measured in four matched rounds taken about 7 to 9 seconds apart while the sauna was heating. A third single-bulb heater appears in the photo only as a reference for the glow comparison. The ± figures on this page show how much the four rounds varied.
Which Sun Home saunas use the tested heaters?
The report describes a single-bulb heater and a double-bulb heater on the rear wall of the tested sauna, plus a glass-faced front heater and floor heater. We have not yet published which models and hardware versions use each tested heater. Carbon far-infrared panels were not part of this study.
Can I read the full report?
Yes. Read the complete 15-page Surface Optics report. See also our heater emissivity testing page and our safety and testing page.
Sources and verification
- Surface Optics Corporation, "Thermo-Optical Performance Characterization of Infrared Sauna Heaters" (PDF), prepared for Sun Home Saunas, dated September 21, 2026, 15 pages. Page map: executive summary and primary finding, page 1; fundamentals of thermal emission, page 2; measurement and data-reduction method, page 3; room-temperature surface properties, page 4; heater identification and visible incandescence, page 5; single- versus double-bulb emittance and camera calibration, page 6; emissivity-corrected thermography, page 7; derived radiative performance, page 8; spatial distribution, page 9; additional heater surfaces and exterior solar-optical properties, pages 10 to 11; conclusions, page 12; temperature-weighted hemispherical emittance, page 13; ET-100 band reflectance, page 14; 410-Solar and primary radiometric data, page 15.
- Instruments: ET-100 infrared reflectometer (six bands, 1.5 to 21 µm, 20° and 60° incidence, three repeats per surface); radiometric FLIR long-wave infrared camera, corrected with the measured camera-band emissivity of each surface; 410-Solar reflectometer (seven bands, 335 to 2,500 nm) for the exterior surfaces.
- Method basis as described in the report: Kirchhoff's relation for converting reflectance to emittance on opaque surfaces (page 2); temperature-dependent hemispherical emittance from Planck weighting of the room-temperature spectrum (pages 2 and 13); Stefan-Boltzmann calculation of surface-equivalent radiant exitance from the corrected temperature field (page 3).
- First study: our heater emissivity testing page and the Surface Optics optical characterization report (PDF), measurements performed August 31, 2026.
- Related Sun Home testing: EMF, VOC and materials testing, how our EMF testing works and Sun Home technology, explained.
Questions about this report or the measurement method? Contact us.