A wood-burning sauna heater is at the heart of Finnish sauna culture. The cheerful crackling of logs and the beautiful dance of a living flame in the dim light are the ultimate sauna pleasures. The steam produced by a wood-burning heater is at its best when it is soft and pleasantly moist.
A good heater can withstand intense heat. Or can it? Can wood pellets be used in a sauna heater? When is it time to replace an old wood-burning heater with a new, low-emission one, and is a wood heater a good choice for a new sauna? This article answers these questions and explains how to choose a wood heater that produces excellent steam.
Wood-burning heater or electric heater?
The main difference between heaters is how they heat. An electric heater requires electricity to operate, while a wood-burning heater uses wood to heat. A wood-burning heater is an excellent choice where electricity is not readily available.
A wood heater is also well suited to a small house, and choosing one as the heart of the sauna should be considered during the design phase of the house. This helps avoid potential changes to the ventilation ducts and smoke exhaust system after the building is completed.
Types of wood-burning heaters
Wood-burning heaters differ according to their heating type. There are continuous-burning and storage heaters. There are also outdoor and indoor heaters. Outdoor heaters require a chimney for smoke exhaust, while indoor heaters are smoke saunas. This article focuses solely on outdoor heaters.
A continuous-burning heater produces heat as long as wood is burning in its firebox. Wood can also be added during the sauna session. A continuous-burning heater heats up faster than a storage heater.
A storage heater, or single-burn heater, stores heat in the heater stones, and the heater is heated up all at once. It takes a few hours to heat a storage heater. A storage heater is also safer to use because there is no open flame during the sauna session.
There are also combinations of storage and continuous-burning heaters. The heater may also have a water tank for heating wash water. Such a heater is well suited for a sauna where running or preheated water is not available.
Choose a heater powerful enough for the right-sized sauna
Choosing a heater begins with determining the volume of the space to be heated. The volume is calculated by multiplying the height of the sauna room by its length and width. The result is the volume in cubic meters. The calculation can also take into account the amount of cold surfaces by adding the square meters of stone and glass surfaces and multiplying the total by 1.2–1.5. The actual size of the sauna determines the maximum power of the heater. It is advisable to slightly oversize the heater for a cold-storage outdoor sauna to ensure the sauna gets warm even in severe frosts.
Modern wood heater manufacturers provide a power rating for wood heaters relative to the volume of the sauna to be heated. For example, Tulikivi wood-burning heaters have a power rating of 20 kW and are suitable for saunas with a volume of 8–20 m³.
The advantage of a wood-burning heater is the waste heat it produces, so a slightly smaller heater can heat effectively compared to an electric heater. Wood heaters come in many models, from narrow to large. The heater should be chosen according to the space and its installation location, taking into account the safe use of the heater.
Wood heater safety distances – A fire-safe heater
The safety distances required for wood heating affect the choice of a wood heater. Depending on the manufacturer, the required clearance for wood heaters from wooden structures is approximately 50 cm, and 5 cm from non-combustible materials such as tiled or stone walls. A wood heater also requires more clearance from the ceiling than an electric heater.
Modern wood heaters are designed with shorter safety distances and do not require non-combustible walls around the heater.
For example, the surface of a Tulikivi wood heater does not become dangerously hot because the heater comes standard with radiant heat shields at its base and sides, so separate fireproof plates do not need to be installed on the walls or floor around the heater.
Carefully check the manufacturer's instructions on safety distances before purchasing the heater.
Positioning the heater
The most important factor in positioning a wood heater is the location of the chimney. It is advisable to choose a heater model that fits the existing chimney. The heater manufacturer provides information on the location of the heater's chimney connection relative to the heater.
Adding wood must also be taken into account when choosing a heater. Adding wood is easiest with a heater whose firebox is located in a separate area from the sauna room itself.
During the design phase of a new house, the heater's location can be planned so that a fireplace heater can be used, with the firebox also serving as a fireplace.
Proper ventilation
In a wood-fired sauna, ventilation is extremely important for the comfort of the sauna users as well, because the heater consumes a lot of air when wood is burned. Fine particles can also enter the air, affecting the quality of the breathing air. The air intake for a wood heater is often located near the heater's smoke outlet so that the heater receives the air it needs for combustion, and some of the air passes through the heater into the sauna, heating the space.
Replacing a small heater with a larger one may also affect the amount of air required if the firebox of the new heater is larger than the old one. In this case, the amount of fuel that can be burned may increase. When choosing a heater, ensure that the fuel being burned receives sufficient supply air.
When a heater is heated with wood, the heater's chimney connections must be in good condition, so leave this work to a qualified professional.
The importance of heater stones in choosing a heater
The number of stones in the heater is directly proportional to the heat of the steam produced. A heater with a large number of stones heats up more slowly but retains the heat from the burned wood for longer. A smaller heater is better suited to cramped saunas where a large heater cannot be installed.
The stones used in wood heaters are larger than those used in electric heaters. Stones that are too small pile up more tightly and prevent air from flowing through them. Stones that heat up quickly also crumble faster than larger stones. A large mass of stones withstands wear for longer. It is always advisable to use high-quality stones in the heater.
When should an old heater be replaced? Can an old heater be upgraded?
A wood heater can be upgraded with a LumoX EkoAir S air controller to become more efficient in its combustion technology and burn more cleanly, provided it is otherwise in good working condition. Upgrading the heater is worth doing for the reduced wood consumption and lower fine particle emissions alone. If the heater has been in use for a long time, its components will eventually wear out due to exposure to hot flames, and when problems arise, it is time to purchase a new heater. The falling of heater stones onto the ash pit is a sure sign that it is time to replace the old heater.
Tips for using a wood-burning heater
- Remove old ash and unburned wood after every use. Empty the ash into a lidded metal container safely when it is cold.
- Light it quickly. Use small, dry pieces of wood. Use a firestarter to light it.
- Burn dry, clean wood.
- Do not burn rubbish.
- Burn in several batches. Do not fill the firebox. Start heating with small pieces of wood and increase the size toward the end. Add wood only when the flame begins to die down.
- Good combustion requires air. Ensure good draft.
- Make sure the chimney is swept regularly. To ensure fire safety, fireplaces in permanent residences must be swept once a year, and those in summer cottages every three years.
- Monitor the color of the smoke: if the smoke is dark or brown, combustion is inefficient. The smoke is colorless when combustion is efficient.
Fireplace heater
A Tulikivi Kinos fireplace heater is heated in a room next to the sauna through an open door. This means there is no need to enter the sauna during the heating phase to add wood. A stone-clad fireplace heater mantle can be installed around the heater's glass door, allowing the firebox to also serve as a modern, sleek fireplace.
LumoX EkoAir S – Savings on heater heating
You can increase the heater's efficiency and reduce fuel costs with an add-on device such as the LumoX EkoAir S. The LumoX EkoAir S preheats the combustion air and directs it over the wood. This allows the smoke gases to burn in the firebox. This way, the wood burns cleanly and uses considerably less fuel, and fine particle emissions are significantly reduced.
The Lumox EkoAir S is suitable for almost any heater. Thanks to controlled air circulation, it is easy to light. When wood burns cleanly, it also burns more slowly. At the same time, it significantly improves the heater's efficiency and reduces the number of times wood needs to be added during heating.
Cleaner combustion extends the life of the heater and chimney. It also reduces the formation of creosote. At the same time, the amount of ash and other combustion residue is reduced thanks to cleaner combustion.