Frost and Steam is reader-supported. When you buy through links on this page, we may earn a commission at no extra cost to you. Read our Affiliate Disclosure.
A sauna needs about six changes of air per hour, according to both Tylo and Harvia. The outlet is the hard part: most Tylo guides put it high, and Harvia puts it near the floor.
Every figure comes from a manufacturer manual or code text we opened. Conversions and arithmetic are ours, and we have not built or tested any sauna. For the overview, see our guide to planning and building a home sauna.
The short answer
- Plan for about 6 air changes per hour. Tylo and Harvia both say so. Section J of Harvia’s US manual says 5.
- Tylo: inlet under the heater, outlet high and diagonal to it, same area as the inlet.
- Tylo vent area: at least 0.3 sq in per sq ft of floor (about 21 cm² per m²). Under 31 sq ft, use 9.3 sq in (60 cm²).
- Harvia, electric heater: supply pipe 2 to 4 in (50 to 100 mm) across. Exhaust near the floor, far from the heater, twice the supply diameter.
- Follow the manual for the heater you buy. That manual is what the warranty covers. Do not mix one maker’s outlet height with the other’s sizes.
How do the vent sizes compare?
Tylo sizes by floor area and makes the outlet equal to the inlet. Harvia sizes by pipe diameter and makes the outlet larger. The same room gets different openings.
Take a 6 by 8 ft sauna, which is 48 sq ft (4.5 m²). Tylo’s Sport USA installation guide (PDF p. 4) gives the formula: at least 0.3 sq in of vent per sq ft of floor. That is 0.3 x 48 = 14.4 sq in (93 cm²) for the inlet, and the same for the outlet.
Harvia gives diameters in millimetres. Converted to inches, a supply pipe of 2 to 4 in (50 to 100 mm) has an area of 3.0 to 12.2 sq in (19.6 to 78.5 cm²). The square-inch figures are our conversion from the manual’s metric values, which is why 2 in reads as 3.0 sq in rather than 3.14.
An exhaust of 4 to 8 in (100 to 200 mm) has 12.2 to 48.7 sq in (78.5 to 314 cm²). These are our calculations: doubling a diameter gives four times the area.
They are different designs, not one rule stated twice.
Where do Tylo and Harvia put the outlet?
Tylo says high, Harvia says low. Tylo’s guides for Sport, Pure and Elite, Commercial and Crown place the outlet high on the wall or in the ceiling.
Harvia’s electric heater manual places it near the floor.
| What the manual says | Tylo | Harvia (electric heater) |
|---|---|---|
| Air changes | About 6 per hour (Sport, Pure and Elite, Bliss) | 6 per hour (KIP manual PDF p. 4, support article). Section J says 5 (PDF p. 9) |
| Inlet | Straight through the wall under the heater’s centerline (Sport). Beneath the heater (Bliss) | Natural ventilation: under or next to the heater. Mechanical: above the heater (KIP manual) or in the upper part of the sauna (support article) |
| Outlet position | High on the wall or in the ceiling, diagonal to the inlet (Sport, Pure and Elite, Commercial, Crown). Diagonal, below the upper bench, “in typical installations” (Bliss) | Near the floor, as far from the heater as possible (KIP manual PDF p. 4, support article). Section J: opposite wall, “if possible”, 10 to 12 in (250 to 300 mm) from the floor |
| Outlet size | Same area as the inlet | Pipe diameter twice the supply pipe diameter |
| Mechanical ventilation | Not recommended (all except Bliss, which does not say) | Allowed (PDF p. 4), mandatory if the exhaust is in the washroom. PDF p. 8: “a fan does not belong in the Sauna” |
Tylo’s Bliss manual words the outlet differently
The Bliss manual says: “In typical installations, locate the vent on a wall diagonally away from the heater below the upper bench.”
The Bliss manual gives no bench height, so we cannot say in inches how much lower that is than “high on the wall or in the ceiling”. What is clear is that Tylo’s own documents do not describe the same position.
Tylo’s documents also differ on UL 875. The Sport USA guide recommends that ventilation openings meet it. The Bliss manual says they must.
Harvia’s manual says 6 changes in one place and 5 in another
On PDF page 4, Harvia’s KIP manual says the air should change six times per hour. Section J, on PDF page 9, says vents “should allow air to change 5 times per hour”.
This is the one point where the manual contradicts itself.
Section J only adds exact positions. The intake is 2 in (50 mm) from the floor. The outlet is on the opposite wall, “if possible”, 10 to 12 in (250 to 300 mm) up.
That fits page 4’s “near the floor, as far away from the heater as possible”.
Harvia’s support article adds a wood-burning case. With gravity ventilation the outlet sits near the roof, far from the stove. That is a different heater, but Harvia does put an outlet high in that setup.
What neither maker explains
None of these documents gives a reason for the outlet height. Neither Tylo nor Harvia explains why one places it high and the other low.
Tylo’s Bliss manual says the far side of the room near the ceiling is 15°F to 25°F (8 to 14°C) cooler than above the heater.
It also says ventilation narrows the gap without removing it. It does not tie this to the outlet, so we cannot say which placement is better.
We read four Tylo guides and one Harvia manual plus one Harvia support article, and they line up this way consistently.
What does this mean for your build?
Pick the heater first, then lay out the vents from that heater’s manual. Follow the manual for the heater you buy, because that is what the warranty covers.
The model codes we read also send you back to the manufacturer’s instructions.
- Read the ventilation page of your heater manual before you frame the walls.
- Mark the inlet and outlet the way that manual draws them, and keep to its sizes.
- Keep the inlet and outlet open to the same space. Tylo says the outlet must not lead outdoors.
- Its Bliss manual says both vents “MUST open to the same exterior room/space/environment”. Neither says how that applies to a freestanding outdoor sauna, so ask Tylo.
- If you close the gap above the ceiling, Tylo says to leave at least one vent hole on the same wall as the door.
- Keep supply air off the temperature sensor. Harvia says to alter the ventilation if the sensor’s minimum distance is not met.
- If a kit ships with its own vents, ask the kit maker and the heater maker to confirm the plans fit.
The makers agree on a few things. Both give about six changes per hour (Harvia’s section J says five). Both put the outlet away from the heater or inlet, and both link ventilation to the temperature sensor or cut-out.
Does building code add anything?
Sometimes, and mostly by pointing back to the manufacturer. Which code applies depends on the building.
We read the 2024 International Mechanical Code (IMC) in the State of Georgia’s published edition on UpCodes.
Section 914.5 asks for a ventilation opening of at least 4 by 8 in (102 by 203 mm) near the top of the door.
The text does not say whether that opening is the inlet or the outlet.
The 2024 International Residential Code (IRC) covers detached one- and two-family dwellings and their accessory structures (R101.2). A home sauna may fall under it instead.
Its section M1902.2 says sauna heaters “shall be installed in accordance with the manufacturer’s instructions” and shall comply with UL 875.
It has no 4 by 8 in rule. We read it in the General Services Administration’s edition on UpCodes.
Adoption varies and some places amend the text, so ask your building department which code and edition apply.
UK and EU readers
Harvia’s support article and Tylo’s international Sport guide use metric units. Harvia gives a 2 to 4 in (50 to 100 mm) supply, for example.
We did not verify UK or EU building rules for sauna ventilation, so ask your local building control.
When to call a professional
Have a licensed electrician wire the heater, and ask your building department about the vents. We are not electricians or inspectors, and local rules apply.
Tylo warns that incorrect ventilation can dry out the wooden panels and pose a fire risk in certain circumstances. If your plan departs from the heater manual, ask the manufacturer before you build.
Common questions
Tylo and Harvia both say about 6 per hour. Section J of Harvia’s US KIP manual says 5, so check the manual that comes with your heater.
Tylo says through the wall under the heater’s centerline. Harvia says under or next to the heater for natural ventilation, and above it for mechanical.
Tylo says high on the wall or in the ceiling, diagonal to the inlet. Its Bliss manual says below the upper bench “in typical installations”. Harvia says near the floor, far from the heater; follow your heater’s manual.
Tylo says mechanical ventilation is not recommended, because poor air exchange can affect the heater’s temperature cut-out. Harvia’s KIP manual allows it on PDF p. 4, yet p. 8 says “a fan does not belong in the Sauna”. Ask Harvia which fan that means before you install one.
Sometimes. The 2024 IMC, read in Georgia’s edition, asks for a 4 by 8 in (102 by 203 mm) opening near the top of the door. The 2024 IRC M1902 sends heater installation back to the manufacturer’s instructions; ask your building department which code applies.
Tylo says it can dry out the wooden panels and pose a fire risk. Harvia says supply air must not cool its temperature sensor.
Next steps
- Planning and building a home sauna: site, power, ventilation and permits
- Sauna heaters: kilowatts, brands, and what your electrician needs
- Home saunas: barrel, cabin and infrared
Sources
- Harvia KIP owner’s/operator’s manual, US version: PDF pages 4, 8 and 9
- Harvia Support: Ventilation in the sauna: updated January 29, 2026
- Tylo Sense Sport USA installation guide
- Tylo Sense Sport installation guide, international
- Tylo Sense Pure and Elite USA installation guide
- Tylo Sense Commercial installation guide
- Tylo Crown Commercial installation guide
- Tylo Sense UB (Bliss) manual, revision C, April 8, 2026
- 2024 International Mechanical Code, chapter 9, State of Georgia edition on UpCodes: sections 914.2 and 914.5
- 2024 International Residential Code, chapter 19, GSA edition on UpCodes: section M1902
- 2024 International Residential Code, chapter 1, GSA edition on UpCodes: section R101.2
All sources checked 5 October 2026.