Sauna Installation Guide: Sizing, Materials and Cost Factors (2026)

For the interior lining we look for three things: low thermal conductivity (it does not burn when touched), no resin bleeding, and no cracking through wet-dry cycles. Measured against these three criteria, timbers differ clearly from one another.

Nordic spruce and thermally modified spruce are the most common and balanced choice for a classic Finnish sauna; with their light colour, low resin risk and reasonable cost, they are the material we use in most residential projects. Alder gives a softer touch and a warm colour, and is comfortable on benches. Western red cedar, with its aromatic scent, natural moisture resistance and low thermal conductivity, is the upper segment; its cost is clearly above that of spruce.

Aspen, being resin-free and almost colourless, suits sensitive skin, particularly on benches and backrests. Resinous timbers such as pine bleed resin at high temperatures and can burn the skin, which is why we do not use pine for sauna interior linings. Which timber we recommend depends on the intensity of use, the budget and the desired appearance.

The real variable that determines cost is not the floor area but the volume to be heated, that is, the cubic metres. Of two saunas with the same floor area, the one with the higher ceiling needs a more powerful heater and uses more cladding timber. That is why we build the price per m³ and show, item by item, what makes up the figure.

The main items of a sauna quote are: the load-bearing frame and insulation (thermal insulation and vapour barrier), interior and exterior timber cladding, bench and backrest joinery, the sauna heater (electric or wood-burning) and control panel, the glass door, lighting and ventilation grilles, and finally the installation labour. None of these items is a luxury; each is necessary for either the safety or the lifespan of the sauna.

Heater output is also directly linked to volume: roughly 1 kW of installed power is planned for each cubic metre, and this value is raised if there are glazed surfaces and external walls. So a 6 m³ sauna needs a heater of 6-8 kW. Choosing the wrong heater for the volume means a sauna that either does not heat up or consumes excessive energy.

Quotes of this kind usually leave something out: the insulation gets thinner, the vapour barrier is skipped, the timber thickness drops or the ventilation is forgotten. These shortcomings go unnoticed in the first year and show up in the second or third year as darkened timber, condensation and mould.

A proper sauna quote states the volume, the timber species and thickness, the insulation detail and the heater output clearly. When you look at a quote, read the list of items beneath the price: if the vapour barrier, ventilation and warranty are missing, that price is the price of an incomplete sauna.

We do not give a fixed price without a site survey; every space is different and the right figure only emerges from measurements taken on site.

In the great majority of residential use an electric heater is chosen: you set the temperature and time from the control panel, no chimney is needed, and it can be installed inside a flat. Modern control units carry overheating and time cut-off protection; we regard these protections as standard.

A wood-burning heater gives a higher peak temperature and a traditional sauna atmosphere; it makes sense in a standalone garden sauna. However, it needs a chimney, a non-combustible floor and fuel storage, and in an apartment flat it often cannot be installed.

Whichever heater you choose, matching the output to the volume and the safety of the controls are not up for negotiation. From the heaters and controls in our sauna systems product range, we match the capacity suited to your volume.

The work proceeds in three stages.

The first stage is the site survey and design: we measure the space, listen to how you plan to use it and present our timber and heater recommendation with an itemised list. The second stage is the infrastructure and frame: the insulation, vapour barrier, electrical and ventilation lines are laid; this hidden layer is the part that determines the sauna's lifespan. The third stage is the timber cladding, bench joinery, heater installation and commissioning.

At handover we provide, together with the key, information on use and care: the first firing, protecting the timber and why the ventilation must be left open. A well-built and correctly used sauna gives decades of service. When salt room construction is added alongside it, the relaxation sequence extends to three steps: dry heat, salt air and cooling down.