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Small details become expensive problems once installation begins. We ask the questions early, so a mismatched part, an overlooked requirement or an installation issue gets caught while it is still easy to fix.

Our job does not end when your order ships. We stay available through installation and beyond. If something needs attention, we stay involved, work the problem, and help see it through.

We want you to feel good about choosing Sauna Marketplace long after your first session, and confident recommending us to a friend. That standard guides the advice we give, the products we sell, and the way we take care of our customers.

Sauna and heater customers also receive free shipping on sauna accessories for life.

Planning a sauna, or need help with one you purchased from us? Our founders have built saunas from the crate up and both run saunas at home. New customers and existing Sauna Marketplace sauna and heater owners can Open the 3D planner.

Includes

What Is Included

Includes the product and configuration selected above. Hardware, controls, stones, venting, and accessories are not included unless specifically listed.

See How It Fits for required and compatible products.

Technical Specifications

At a Glance

At a Glance
Heat Source	Wood-burning
Sauna Room Size	Pro 20 Duo: 283 to 706 cu ft · Pro 36 Duo: 494 to 1,271 cu ft
Sauna Ceiling Height	At least 81.1 in floor to ceiling
Power	24.1 and 31 kW
Mounting	Floor-standing
Loading	Through the wall, from the next room
Stones	88 to 132 lb, by size
Warranty	2 years home use
Made in	Finland

Model & Application

Model & Application
Brand	Harvia
Catalog Product	Harvia Duo Fireplace and Wood Sauna Stove Combo
Heater Type	Wood-burning sauna stove
Exact Models	PRO 20 DUO: WKPR20DUOS; PRO 36 DUO: WKPR36DUOS

Sauna Sizing

Sauna Sizing
Sauna Room Volume	PRO 20 DUO: 282-706 CU. FT.; PRO 36 DUO: 494-1271 CU. FT.

Fuel & Venting

Fuel & Venting
Fuel	Wood

Dimensions & Weight

Dimensions & Weight
Heater Dimensions	PRO 20 DUO: 17" W × 31" D × 30" H; PRO 36 DUO: 20" W × 31" D × 40.9" H

Through-Wall Installation

Through-Wall Installation
Wall Opening, Minimum	15.9 in wide x 19.1 in tall from the floor, Pro 20 Duo and Pro 36 Duo. Harvia notes the opening dimensions change if the protective bedding is used.
Wall Thickness, Maximum	4.7 in per the manual text; its Figure 11 table shows 5.9 in. Plan on 4.7 in. Concrete or brick.
Non-Combustible Wall Around the Opening, Minimum	Pro 20 Duo: 20.3 in beside the opening, 56.3 in overall width. Pro 36 Duo: 21.9 in beside, 59.5 in overall (Figure 11, D and E).
Steel Chimney Note	With a Harvia steel chimney the non-flammable wall through which the stove is installed must extend up to the roof (thin non-combustible partitions such as the Harvia Duo glass wall excepted).

Stone Capacity & Performance

Stone Capacity & Performance
Rated Power	PRO 20 DUO: 24.1; PRO 36 DUO: 31
Stone Capacity	PRO 20 DUO: 88 lbs; PRO 36 DUO: 132 lbs

Included & Required

Included & Required
Required, Not Included	PRO 20 DUO: 88 lbs of Split-Face Sauna Stones (Qty 2 x 44 lbs of 4 to 6 in stones); PRO 36 DUO: 132 lbs of Split-Face Sauna Stones (Qty 3 x 44 lbs of 4 to 6 in stones)

Materials & Finish

Materials & Finish
Construction	Steel with stainless-steel outer casing

Certifications

Certifications
Certifications	CE, EAC

Use the attached current manual and a qualified installer for final sizing, wiring, clearances, venting, and local-code compliance.

How It Fits

How This Product Fits the System

What it is used for

A wood-burning sauna heater that heats the room and stone mass for traditional löyly. Treat the stove, chimney, floor protection, clearances, combustion air, ventilation, and stones as one installation system.

What to plan

Through-wall opening: at least 15.9 in wide x 19.1 in tall from the floor in a concrete or brick wall; plan on 4.7 in maximum thickness (the manual text says 4.7 in; its figure table says 5.9 in). The non-combustible wall must continue at least 20.3 in (Pro 20 Duo) or 21.9 in (Pro 36 Duo) beside the opening, and with a Harvia steel chimney it must reach the roof.
Size from adjusted sauna volume, including the effect of glass, masonry, and other uninsulated surfaces; do not size from floor area alone.
Match the selected model's power or fuel, voltage, phase, circuit, wire, control, stone, and venting requirements before ordering.
Treat clearances, ceiling reference planes, ventilation, guarding, floor protection, and service access as one room-layout decision.
Follow the current installation manual and use a qualified installer.

Designed to work with

Model-specific replacements and compatible system components.

Harvia HL3M Safety Rail for Virta HL110, HL70SA and HL90SA | Wood Designed for the same heater or control system; confirm compatibility with the selected model.
Harvia HL3S Safety Rail for Virta HL70 and HL90 | Wood Designed for the same heater or control system; confirm compatibility with the selected model.
Harvia SASPO240 Safety Railing for Legend 240 and 300 Wood Stoves Designed for the same heater or control system; confirm compatibility with the selected model.

Attachments

Current Installation Manual - Harvia Pro Duo and SL - June 2026

Current Pro Duo and SL manual recovered from the matching current US source. Exact source bytes and model scope verified by Sauna Marketplace on 2026-08-21.

View PDF Download

Current Data Sheet - Harvia Pro 20 Duo WKPR20DUOS - June 2026

Exact WKPR20DUOS technical data sheet. Exact source bytes and model scope verified by Sauna Marketplace on 2026-08-21.

View PDF Download

Gallery

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Harvia Duo Fireplace and Wood Sauna Stove Combo

The Harvia DUO line is a stunning best-of-both-worlds fireplace and sauna spanning two rooms. It’s the most elegant solution to for through-wall sauna operation.

Wall opening: at least 15.9 in wide x 19.1 in tall from the floor, in a concrete or brick wall; plan on 4.7 in maximum wall thickness.

Build Your Quote:

Price range: $2,871.00 through $3,415.00

Size

Clear

Stones

Chimney Kit

Harvia Stainless Steel Chimney Kit for Flat Roof +$1,433.00

Harvia Wood Pipe Adapter 4.5" Euro to 6" USA +$116.67

Water Tank Heater

Harvia Pro Floor Protector

The Harvia protective bedding is used when a fireplace or stove is installed onto a waterproofed tile or hardwood floor. Made of aluminum-zinc coated steel, painted black.

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What to Expect

Compatibility Check

We look for any issues with your order.

Same Day

Ready to Ship

Warehouse schedules shipment

1 Day

Freight Shipping

Our trusted shipping partners will schedule a delivery time and delivery your package to the ground.

4-14 Days

'Whatever-It-Takes' Support

Unlimited access to tech support from SaunaMarketplace.com and Harvia.

Support Details

This order is fulfilled through our US distribution network. That means you have full access to their top-notch customer service and tech support, as well as SaunaMarketplace.com and Harvia support. We're with you and your contractors until it's operating as it should, no matter what.

Before your order ships, we provide contact information and reference numbers for each.

Warranty 2 Years

Warranty Docs

Setup, Operation, and Maintenance

Harvia Pro Stoves are built with safety in mind. These manuals and documents will help ensure a safe, great performing heater for years to come.

Pro 20 Documents

Manual

Catalog

20 Pro Data Sheet

Harvia 20 Pro Declaration of Performance

Harvia Pro Safety Sheet

Pro 36 Documents

Manual

Catalog

Hariva-PRO36-Accessories Hariva-PRO36-datasheet Hariva-PRO36-DOP Hariva-PRO36-Safety Hariva-PRO36-Spare-Parts

Harvia Pro 20 Duo and Pro 36 Duo

The Pro Duo stoves install in an opening in a concrete or brick wall. The stove body and stones sit in the sauna, and the fire chamber extension passes through the wall so the glass firing door and the ash box face the room next door. You add firewood and empty the ash box from outside the sauna, and the fire shows through the glass in that room.

The Pro 20 Duo (WKPR20DUOS) is rated at 24.1 kW for sauna rooms up to 706 cu ft and holds up to 88 lb of stones. The Pro 36 Duo (WKPR36DUOS) is rated at 31 kW for rooms up to 1,271 cu ft and holds up to 132 lb. Both have a stainless steel outer shell, a 4.5 in flue connection on top, and take firewood up to 15 in long. The firing door can be hung to open left or right.

Setup, Operation, and Maintenance

Harvia Pro Stoves are built with safety in mind. These manuals and documents will help ensure a safe, great performing heater for years to come.

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Planning guides: Sauna heater calculator Wood sauna stove guide