A kachelofen, also known as a masonry heater, is an extremely efficient, wood-burning heating stove made of masonry materials like bricks or soapstone. Kachelofens have been used for centuries in cold climates to provide steady, gentle, pleasant heat throughout the home.
Unlike a metal wood stove, a kachelofen has enough mass to absorb a large proportion of the heat from a brisk 1-2 hour wood fire and radiate it slowly over the next 8-20 hours. This allows a kachelofen to provide an entire day’s worth of heat from a short fire, without the peaks and valleys of heat output from a metal stove. They burn very cleanly and safely while getting the most out of the wood fuel.
Constructing a masonry heater requires time, skill, and the right materials, but can be a very rewarding DIY project. This article provides step-by-step instructions on planning, designing, and building your own kachelofen from scratch.
You can find a more detailed instruction pdf here
Planning and Designing Your Kachelofen
The first step is determining the right size kachelofen for your space. As a general rule of thumb, you need about one square foot of baking chamber floor space for every 100 square feet of space to be heated. Kachelofens can range from small 3 foot units to larger 8 foot designs. Make sure to account for minimum clearances to combustibles as outlined in building codes.
You’ll need to create detailed plans for your DIY kachelofen, indicating all dimensions, shapes, and materials. Some key elements to include in your design are:
- Firebox – Where the wood fuel is loaded and initial combustion occurs. Fireboxes are typically 1-2 feet wide and 1 foot deep.
- Smoke channels – Channels that route hot gases from the firebox through the interior of the heater to heat up the masonry mass.
- Baking chamber – The main central area where most heat is emitted. Line this with firebricks and include vents.
- Masonry mass – Soapstone, brick, tile, or other masonry materials with good heat retention.
- Air gaps – Small gaps between firebrick interior and outer masonry to force heat transfer.
- Insulation – Perlite or vermiculite used to fill air gaps.
- Footprint – Dimensions of the floor space needed.
- Facade – Decorative facing bricks or tiles on the exterior.
- Hearth extension – Stone, tile, or brick extending in front of kachelofen.
- Mantel – Constructed over top of the heater.
It’s a good idea to review various kachelofen designs online to get inspiration for your own plans.
Constructing the Foundation
Kachelofens weigh anywhere from 1-4 tons, so a proper foundation is critical. The best option is to pour a concrete slab foundation. Make sure it is sized appropriately and can handle the load. The slab should be perfectly level in all directions to evenly distribute the weight.
You can also build a custom raised brick or stone hearth for your kachelofen to sit on. Just ensure it is structurally stable.
Building the Firebrick Core
The inner firebox, smoke channels, and baking chamber make up the functional core of the heater. This section needs to withstand extremely high temperatures, so it should be constructed using high heat rated firebricks jointed with fire mortar (rated for 2000°F+).
Refer to your plans to lay the firebricks for the desired shape and size of firebox, smoke channels heading upwards or to the rear, baking chamber dimensions, and vents through the exterior layers. The routing of smoke channels should maximize heat transfer through the surrounding masonry mass.
Adding Outer Masonry Layers
Once the inner firebrick core is complete, you can build additional masonry layers around it to absorb and radiate heat. Materials like brick, soapstone, granite, ceramic tile work well. Leave at least a 1 inch gap between the firebricks and outer layer to form an air channel.
It’s best to build up the outer layers progressively from the ground upwards, interlocking the pieces in a self-supporting way. The outer layer should be at least 4 inches thick for heat storage capacity. Shape according to the footprint in your plans.
Installing Insulation
The air gap between the firebricks and outer masonry needs to be filled with insulation to force the heat through the exterior layers. Vermiculite and perlite are common options suited for high temps. Make sure there are no gaps where heat can bypass the outer masonry.
Adding the Chimney
Use chimney pipe running from the top of the smoke channels through the ceiling and roof to safely exhaust combustion gases outside. The chimney pipe should be stainless steel or have an insulative liner. Surround with an extra layer of fireclay liner for added insulation.
Applying the Facade
To complete the aesthetic exterior of the masonry heater, apply facing materials like decorative tiles, bricks, or quarried stone. This ties the whole build together into a beautiful showpiece for heating. Consider adorning with custom artwork or designs.
Don’t forget to allow space to build out a hearth extension and mantel over top of the kachelofen. These help protect surrounding flooring and walls. You can customize designs with stone, tile, or wood.
Final Steps and Maintenance
Before firing up your DIY kachelofen, follow curing times for mortar and masonry specified on materials. Confirm all clearances meet building code requirements. Slowly bring up to temperature on the first few burns.
Provide a moisture meter and wood storage area for properly seasoned wood fuel. Avoid burning trash or plastics which release toxins. Have your chimney swept annually. Ashes will need occasional removal. Enjoy a lifetime of efficient, sustainable heating!
