Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension

Create the authentic atmosphere of a traditional Finnish sauna with the Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension. Expertly designed and manufactured in Finland, this premium wood-burning sauna heater delivers exceptional heating performance while allowing you to conveniently load firewood from an adjoining room. Perfect for small to medium-sized saunas between 283 and 706 cubic feet, the Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension combines a powerful 24.1 kW heating capacity with innovative engineering, making it an ideal choice for homeowners, cabins, and luxury outdoor saunas.

With its integrated firebox extension, elegant cast-iron glass door, and durable steel construction, the Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension provides both an authentic sauna experience and the convenience of heating two spaces simultaneously.

Why Choose the Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension?

The Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension is designed for sauna owners who want the warmth and ambiance of a wood-fired sauna without the inconvenience of carrying firewood into the sauna room.

Its unique SL (Separate Loading) design extends the fire chamber through the wall, allowing you to feed wood from an adjacent room while keeping your sauna clean, quiet, and free from ash or debris.

Key Benefits

• Authentic Finnish wood-burning sauna experience
• Convenient firebox extension for external wood loading
• Powerful 24.1 kW heating output
• Heats two rooms simultaneously
• Elegant cast-iron framed glass door
• Premium black steel construction
• Designed and manufactured in Finland
• 2-Year Consumer Warranty

Convenient Firebox Extension Design

One of the standout features of the Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension is its integrated firebox extension.

Instead of loading wood inside the sauna, you can conveniently add logs from another room or outside the sauna building.

Advantages include:

• Cleaner sauna environment
• Reduced ash and dust
• Easier wood loading
• Greater convenience
• Ability to heat two rooms simultaneously
• Improved safety

This innovative design makes the heater perfect for backyard sauna buildings, cabins, and traditional Finnish sauna installations.

Powerful 24.1 kW Heating Performance

The Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension delivers an impressive 24.1 kW of heating power, allowing it to quickly warm medium-sized sauna rooms while maintaining comfortable, consistent temperatures.

Recommended sauna room size:

• Minimum: 283 cubic feet
• Maximum: 706 cubic feet

Ideal for:

• Outdoor sauna buildings
• Home wellness rooms
• Lakeside cabins
• Vacation homes
• Cottage saunas
• Commercial wellness retreats

Its powerful output ensures rapid heating and outstanding performance even during colder weather.

Authentic Finnish Sauna Experience

Nothing compares to the atmosphere created by the Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension.

The natural warmth of burning wood combined with heated sauna stones creates:

• Traditional Finnish löyly (steam)
• Comfortable radiant heat
• Relaxing crackling fire sounds
• Natural wood aroma
• Long-lasting warmth
• Even humidity throughout the sauna

The result is a deeply relaxing sauna session that reflects centuries of Finnish sauna tradition.

Elegant Cast-Iron Glass Door

The Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension features a beautiful cast-iron framed glass door that allows you to enjoy the glow of the fire while monitoring the burning wood.

Benefits include:

• Stylish appearance
• Easy fire monitoring
• Warm, inviting atmosphere
• Durable cast-iron construction
• Enhanced visual appeal

The reversible door opening direction also provides added installation flexibility.

Durable Black Steel Construction

Built to provide years of dependable service, the Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension features a rugged black steel body engineered for high-temperature operation.

Construction highlights include:

• Heavy-duty steel construction
• Premium black finish
• Corrosion-resistant materials
• Long-lasting durability
• High-temperature performance

Every heater is precision manufactured in Finland to meet Harvia’s world-renowned quality standards.

Efficient Wood-Burning Performance

The Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension is engineered for clean, efficient wood combustion.

Its optimized fire chamber offers:

• Excellent fuel efficiency
• Consistent heat output
• Reliable combustion
• Easy fire maintenance
• Reduced wood consumption

The efficient combustion system helps maximize heat while minimizing the amount of firewood required.

Sauna Stone Capacity

The Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension holds approximately 88 pounds (40 kg) of sauna stones.

The carefully designed stone compartment provides:

• Gentle steam
• Comfortable humidity
• Even heat distribution
• Traditional sauna performance

Required for operation:

• 88 lbs (40 kg) of sauna stones
• 2 boxes of 44 lb stones
• Recommended stone size: 10–15 cm

Premium sauna stones help maximize heat retention and steam quality.

Easy Installation

The Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension is designed for flexible installation in various sauna layouts.

Installation features include:

• Floor-mounted design
• External firebox extension
• Adjustable installation options
• Reversible door opening
• Compact footprint

Its thoughtful design simplifies installation while enhancing everyday convenience.

What’s Included

Your Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension package includes:

• Harvia Pro 20 SL Wood-Burning Sauna Heater
• Stove Door
• Ash Box
• Installation & Operation Manual
• 2-Year Consumer Warranty

Technical Specifications

Premium Finnish Engineering

Every Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension is designed, engineered, and manufactured in Finland.

Harvia has earned a global reputation for producing high-quality sauna heaters that combine innovative engineering, premium materials, and authentic Nordic sauna traditions.

The heater is:

• CE Certified
• EAC Listed
• Built with premium materials
• Designed for long-term reliability

2-Year Consumer Warranty

The Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension is backed by Harvia’s 2-Year Limited Consumer Warranty, covering manufacturing defects under normal residential use.

Why Buy the Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension?

The Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension is an outstanding choice for anyone seeking the convenience of external wood loading combined with authentic Finnish sauna performance. Its powerful heating capacity, efficient combustion, durable construction, elegant cast-iron glass door, and ability to heat two rooms make it one of the most versatile wood-burning sauna heaters available.

Whether you’re upgrading an existing sauna or building a new outdoor retreat, the Harvia Pro 20 SL Wood-Burning Sauna Stove w/ Firebox Extension delivers lasting performance, premium craftsmanship, and unforgettable sauna experiences.