How to build a shed sauna with a gas bottle sauna stove

Note: This is republishing a post I originally wrote in 2009 in a long dead blog

Disclaimer: this account of sauna building is what worked for us. It is entirely at your own risk to pursue such a project and a fire extinguisher to hand (stored outside of the sauna itself), never bathing alone and leaving if you feel dizzy or overheated are essential for safety. People with heart conditions or not used to sauna bathing should exercise extreme caution with this type of sauna bathing.

This is a basic account of how we built a basic sauna on a small budget, including a wood burning sauna stove. This shed based sauna is not designed to give a lifetimes use but ours has been used frequently for a year or so now and has held up and works perfectly adequately. A fun project for little cash, less then £200 in our case. How cheap you can do yours depends on what you can scavenge so this article is mainly about giving a few ideas and showing what worked for us and how it could be improved.

The criteria we set for our sauna was that it had to be comfortable, capable of reaching proper sauna temperatures, 80’C to 100’C (yes centigrade not fahrenheit), maintaining a good temperature long enough to give a good sauna experience and heating the stones sufficiently to give good loyly (sauna steam)

Where??

We chose the shed. Now obviously you can build a sauna anywhere you wish and basements etc. are popular but for a wood burning variant not in the house is probably wise and easier, i.e. doesn’t require routing a flue/chimney through brickwork etc. and your not going to burn the house down.

building the sauna

Our shed was a pretty standard 8’x5′ size of the type found in many gardens. We chose to partition the shed at about 2/3 to give a 5’x5′ room. This partition was achieved by running battens across at floor and head height with vertical support. To this was screwed a fibreboard partition, obviously to the outside edge of the battens (the pine lining would be screwed to the other side leaving a space for insulation material in between. We cut a door into this and fitting with two hinges and spring closer to push the door shut.

The floor of the shed was lined with pine planks, sanded smooth and splinter free. We put a standard concrete paving slab in the corner where the stove would sit.

The walls and roof were lined with standard tounge and groove pine cladding. A bit of research suggested we ran a risk of this warping and cracking but this has not proved to be a problem. This was screwed to the existing battens to which both the shed outer panels and roof were attached. It is worth pointing out at this point that the wood should not be treated in any way, as the heat of the sauna could cause treated wood to smell unpleasant or even give out noxious fumes. Before screwing the panels on standard rockwool insulation was sandwiched in the gap. Stapled to the outer wall periodically to prevent it sagging.

In the corner where the stove sites we screwed fireproof panels, cement particle board, to both sides, as well as a further on to the ceiling above the stove. Individually these were the most expensive pieces for the sauna at about £12 each. Sadly they are also the only part that has failed slightly. The heat of the stove causing them to bow and crack slightly. Fortunately not sufficiently to be a major problem although would look for an alternative in future.

Ventilation is very important in a sauna. We fitted a sliding grill to the lower part of the door and left a gap at the top of the partition. These gaps at top and bottom help to create a good air flow.

gas bottle sauna stove

There are many ways to build a wood burning stove however we decided to base ours around a gas bottle. A quick scout around the net revealed a popular choice for DIY wood burners are converted gas bottles, mainly as shed heaters funnily enough. We sourced a 19kg one from the tip which worked admirably.

These are the alterations we made to create the stove:

We unscrewed the valve. This was pretty stiff but shifted with a bit of brute force.
Then we filled the bottle completely with water and left it for a day. Before setting to it with the angle grinder we wanted to make doubly sure there were no inadvertant fireworks.
The Gas bottle was a at least a good 4mm thick so cutting by hand would be very time consuming. We decided to invest in a cheap angler grinder from homebase. Despite being only £9.99 it was remarkably effective and make fairly short work of the cutting.
Cuts were as follows: a circular cut to remove around 3/4 of the top (this is for the bucket containing the rocks to sit in). A door around 12″x9″. A small circular cut for the flue just below the curve of the top. This was around 5″ to suit the flue pipe we scavenged.
The removed door piece had a small flange attached to all but the hinge side. We welded it but it could equally be pot riveted, screwed or bolted, depending on what tools you have to hand. This was then bolted in place with some small standard iron door hinges.
For firebars we used some mesh which was scavenged from a rabbit hutch. Two layers cut to size and sat on an existing rim, fortunately at the just the right height innside the bottle worked abmirably.
For the flue we used a piece of double skinned central heating flue. The outer was slit and bent back to form a flange to bolt it to the gas bottle.

A steel bucket was wedged as snugly as possible within the top aperture. We used the angle grinder to fine tune the hole to ensure a good fit.
Stones. Within a sauna it is the stones which store the heat and onto which water is poured to create steam. Given this temperature change it is therefore important to use suitable rocks. Granite is traditional. I gave the stones a good roasting and dropped them into a bucket of cold water a few times to make sure they were sufficiently solid, cracking them together and discarding any that didn’t sound totally solid. These stones were placed in the bucket once the stones were in place.
Before using the stove in a confined space it was important to burned off any paint etc. which could give noxious fumes. At various stages of build we built fires in the stove, outside, to burn off all paint. A quick scrub with a wire brush removed it faired easily after these fires.
The flue was routed through the wall next to the stove. On hindsight routing the chimney through the sauna would probably have been more efficient in heating the sauna.

Furniture

Every sauna needs somewhere to sit. We built a bench out of an old futon, unvarnished. This worked perfectly. Note: all screws in both bench and sauna construction must be well countersunk to ensure lack of contact with naked flesh!!!!!

Running the sauna

Once all assembled we had the delight of fireing it up for the first time without bathers, a dry run so to speak. It took a bit of practice to get the procedure right for creating sufficient temperature, in both the sauna (80c+, 190f+ roughly) and rocks to provide a good sauna experience but this is what worked for us:

Initally building a good hot fire in the stove, leaving this for 20 mins or so then regular stoking every 15 mins or so for 2/3 hours. The longer you do this for the more heat you get into the rocks and the longer it is usable.

Before bathing it is VERY important to give a good couple of ladles of steam to the sauna and leave for 20 mins. This helps to drive off the carbon monoxide and leave a smoke free environment. 10-15 minute stints in the sauna are ideal for effective bathing.

In the absence of a plunge pool, a cold shower or even some cold buckets of water over the head is wonderfully invigorating.

Improvements: There are a few things i would do differently; routing the chimney straight up through the ceiling to maximise heat gain from the stove, better fireproof panels that do not warp or crack, damp proof insulation (this didn’t cause a problem but if unused for a while rock wool could soak up water. Especially in the damp british climate.)