Trumpkin’s Notes On Barrels

 

Barrels are quite popular in the U.S. They have a low initial cost and are fast and easy to ship and assemble. However, and despite marketing claims, they have a number of drawbacks that make them a poor choice for a sauna.

Outside of North America they are purchased either as a novelty or to get around building codes that won’t allow a cabin which would be considered permanent. 

If you are considering buying a barrel. I’d strongly recommend not to do so unless you are buying a larger 8-10’ diameter barrel or a small barrel is truly your only option due to building codes or other constraints.

Barrels under 8-10’ are simply not good for sauna. Some things like overall temperature, humidity level, wood vs electric heat and what wood to use on walls are personal preference. Nobody however likes or wants bad stale air or cold feet or getting blasted with cold air or having the heat sucked out every time the door is opened or breathing mold spores or ….   Those aren’t preferences but undesirables that come with small barrels.

This is an addendum to Trumpkin’s Notes On Building A Sauna that should be read for further detail on why bench heights, ventilation and other elements are so critical and why Finn’s are so adamant about the foot bench being above the stones.

 

Why Are Barrels So Popular?

Building Code/Regulations – Barrels can sometimes be placed nearer to property lines than a stick built cabin style sauna which is a significant advantage in smaller yards. A cabin might require a permit while a barrel not and a barrel might be considered temporary rather than a permanent structure. This is perhaps the one logical reason for choosing a barrel over a cabin.

Perceived Lower Cost – The initial purchase and shipping cost is often lower than alternatives. Long term and operating costs are different however. 

Fast Delivery – If you don’t want to wait a few weeks or months then a barrel is often the better or only option.

Easy and Fast Assembly – Most people can assemble it and have it running in one to three days. 

Attractiveness – They’re cute. 

Size – People say size. However, a cabin sauna on the exact same footprint will provide a very significantly better experience.

Perhaps the big one though is that we don’t know what we don’t know. We lack a good reference for what good sauna is. We think the cold feet and poor air quality in a barrel is normal. It’s not. We compare our barrel to a typical American sauna with cold feet from too low of benches and no löyly because of poor ventilation and our barrel isn’t much worse so it must be a pretty good sauna.

People who have barrels and never experience anything better are often quite happy with their barrel. Especially if they live in a more temperate climate. And that’s rather good. And some people are just not very picky so a poor barrel is just as good for them as the best sauna in Finland. And that’s OK. I’ve a friend who thinks freeze dried coffee is just as good as fresh ground drip and I’m happy for him. However, a barrel owner, once they experience real Finnish sauna, realize what they’ve been missing, what real sauna is like, quickly become dissatisfied and want a real sauna.

 

Why To Avoid Barrels 

Barrels are a true bigger is better thing. A larger barrel, 3m or 10’ in diameter, that has the foot benches above the stones, a heat cavity above the door, bathers heads not too far below the ceiling, good ventilation and a vestibule can work well but smaller barrels, like typical in North America, are not built like this.

Barrels under 8-10’ in diameter do not and cannot provide a good sauna experience. Air quality is quite poor and bathers often do not experience sauna temps (consistent 80-105°c at head and shoulders, no more than 20°c cooler at feet). Uncomfortably cold feet and chilly backs are difficult or impossible to avoid. Here bigger is better. 6’ is better than nothing but compared to a proper sauna is rather awful, 7’ is somewhat better, 8’ done well can likely provide at least a minimally acceptable sauna, 9’ is doable and can almost provide an experience similar to a proper sauna. Sounds dramatic and harsh but is the unfortunate reality.

According to marketing materials the shape is supposed to make the heat roll evenly around bathers, but physics, stratification of heat, doesn’t actually work like that. I’ve a growing collection of photos of people’s attempts at alleviating some of the problems of barrels with boxes on top benches, intricate fan arrangements, tents as vestibules and other stuff. Some of the problems include (somewhat in order of importance);

Too Little Volume Per Bather – The volume of space per person in a barrel is typically much less than recommended which when the door is closed can result in CO2 and pathogen levels increasing quickly and to quite high and unhealthy levels*. People in a little barrel are quite literally breathing each others exhaled breath. High CO2 levels result in people feeling that they need to exit the sauna to get a breath (rather than from heat & löyly) or are feeling light-headed or dizzy. High ventilation rates (assuming good dispersion/mixing which is quite a bit more difficult in a smaller space) can help with this but in such a small space, even with an adequate heater, often results in cold airflow streams on bathers, particularly around their feet. Each time the door opens helps to alleviate the high CO2 and pathogen levels a little but also brings in colder air and allows heat to escape.

One popular 4 person barrel that is 6’ (71”) in diameter by 5.3’ (64”) in length has 148 cubic feet (37 cubic feet per person) which is about a quarter of the 530 cubic feet recommended volume (and less than half of the 315 cubic feet that is considered the absolute minimum for four people).  CO2 levels will increase two to four times as fast in a barrel as a proper sauna.

Bacteria, Mold & Other Fungi – The foot bench (floor in a barrel) in barrel saunas rarely (actually never) maintains the 65°c / 150°f temps necessary to kill most mold and bacteria so growth of these, particularly bacteria, is a common problem in barrels.

Too Low Of Benches – The primary problem is cold feet but often also cold legs and not so hot bodies. The good heat and löyly is above bathers heads in barrels and bathers are down in the cold area (see heat stratification chart in Trumpkin’s Notes On Building A Sauna). Feet should ideally be no more than 15°c / 27°f cooler than our head and generally never cooler than about 60°c / 140°f and these are impossible in most barrels. Good sauna builders will try to avoid having the foot bench, and so any part of bathers bodies, in the lower 1/3 of the space since this area in any sauna is always rather cool.

However, someone laying on the bench or sitting on it with their feet stretched out in front of them will not be as affected by this.

No Heat Cavity Above The Door – A good sauna has a large cavity above the door to store heat. Without this a significant amount of heat escapes each time the door is opened which is uncomfortable for bathers, takes considerable time to reheat and is a waste of energy. This is worse in barrels as the shape effectively channels the heat up and out of the door. It’s like someone designed it to evacuate valuable heat as quickly and efficiently as possible. 

Direct Radiant Heat – Ideally in a sauna you don’t want any direct radiant heat, you want to be heated evenly all over by soft löyly. This is one reason for ‘Feet above the stones’. Bathers in a barrel experience significant direct radiant heat that leaves them hot on the side facing the heater and cooler on the side away from it (which is also the side that get’s blasted with cool air when the door opens). Glenn Aurbach describes it as like being a hot dog – you roast one side and then move over to the other bench to roast the other. That’s not sauna (more like an IR cabin).

No Vestibule – The lack of a vestibule is much more critical with barrels than with proper saunas since a door opening to outside cold air in a barrel results in much greater and faster heat loss. And similarly, since heat is escaping so much more quickly, cold air is entering down below much more quickly.

No Insulation – The lack of insulation not only results in greater energy loss and higher electrical costs but also to less bather comfort. The walls of barrels are sucking heat out much faster than saunas with proper insulation which results in chilly backs for bathers. The few barrels I’ve seen in Scandinavia have been built from heavier 4-7” thick timbers which provide much better insulation.

Leaks and Water Stains – Barrels are notorious for leaking and getting water stains on the inside. Rain or snow hitting a vertical wall such as an outdoor cabin sauna will run down it and stay on the outside, even with thin timber framing similar to a barrel. Rain or snow hitting anywhere above the midpoint of a barrel will run down too, but with a barrel it’s running down to the inside through various cracks. Roofs sometimes help but not always as wind driven rain or snow can still cause problems. Some people find that keeping the door and a window open can help dry it out and others say that frequently heating it up, even when not being used, will help to keep it dry and the water stains at bay.

Low Cost Is Misleading – Marketing materials say that the shape and smaller space to heat is an advantage, that barrels are more energy efficient. There are a few problems with that. First is the lack of a heat cavity and the shape that efficiently channels heat out when the door is opened results in much more heat loss every time the door is opened. The lack of insulation combined with the shape and heat rising towards the uninsulated and leaky roof results in greater heat loss. And, since bathers are seated so low below the heat that’s higher up, a barrel must be heated to a much higher temperature at the ceiling to maintain the same temperature at bathers heads. A rough calculation is that a barrel costs 4-5x as much to heat as a same footprint cabin. 

Some or many barrels may not have a very long lifespan and will need to be replaced or rebuilt sooner. 

There are also costs of add-ons. Many barrel owners find that they need to build roofs over their barrels to prevent leaking, insulate them, add a vestibule, build new higher benches, add better ventilation and other stuff to try to mitigate some of the problems inherent in barrels. And even with all of these additions it is still a much poorer experience than even a very small uninsulated cabin sauna. Overall barrels just do not make good monetary sense.

Can’t Sit Up Straight – In some barrels it’s difficult or impossible to sit up straight for deep breathing or stretching our backs. Leaning back to relax is also not an option unless sitting sideways on the bench (which sometimes results in sitting kind of crooked which isn’t comfortable for our backs).

More: 10 Things About Barrel Saunas and Why We Don’t Build Barrel Saunas.

 

Improving Barrels

If you already have a Barrel.

Raise the benches – As much as possible and then raise the floor (that’s acting as a foot bench) to 16-18” below the benches. Moving the benches in towards the center a bit may allow a bit more head height for raising them. Normally you’d want the foot bench above the stones and sitting benches 18” above that but here that will be difficult or impossible so as high as practicable for each is the best we can do. Going a bit less than 18” bench heights will bring the floor and feet up higher and in this case the benefit of that will likely outweigh the slightly less comfortable shorter bench height. Making some 4”  – 6″ foot stools for people to use might help as well. Be careful about floor to heater clearances though.

Add Proper Ventilation – In electrically heated saunas a fresh supply vent below the heater and exhaust higher up is a recipe for a not so good experience – it results in colder feet and does little to remove the CO2 and pathogens. Instead, try 4 small 2″ – 2.5” fresh air supply holes above the heater (aligned vertical or slightly staggered, beginning about 1/2 to 2/3 of the way from the top of the stones to the ceiling and evenly spaced). And then a mechanical (powered) exhaust below the benches (or ideally below the floor/foot bench) on the opposite end. Figure about 15-20 CFM per person (so 60-80 CFM for a 4 person sauna). This should help to even the temps out a bit, lessen cold feet and will do a better job of removing CO2.

More: Ventilation For Electrically Heated Saunas 

Typically for this ventilation you do not want a mechanical supply, only mechanical exhaust. Mechanical supply can result in too high of air flow velocity in to the sauna which will reduce mixing. Exhaust side only results in supply air being pulled in (rather than pushed in) which results in better and more even mixing. Forced supply can also result in the sauna becoming slightly pressurized which you do not want in a sauna with insulation. However, in a barrel without insulation and with air leaks between the staves you may want the interior slightly pressurized to prevent cold air entering through the leaks. In this case doing both supply and exhaust may be warranted. More here: Improving Ventilation in a Barrel

Create A Heat Cavity – A bit of wood across the top of the door opening that creates a bit of a heat cavity above the door opening may help to preserve heat when the door opens. And since heat isn’t escaping as fast out of the top, then hopefully less cold air will come in near bathers feet. This might be particularly useful if people are coming and going at different times. Careful for people hitting their heads though.

Add A Vestibule – A vestibule of some sort to act as an air lock would prove quite beneficial, though at some point it’s just best to jump straight to building a proper sauna.

 

A Better Barrel?

A cube shaped barrel can alleviate some of the worst problems of round barrels if designed well. They will likely still have problems of no insulation and cold backs as well as a potentially shorter lifespan. The round shape of barrels is critical to the structural integrity so there is some concern about how well cubes will do structurally. 

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Ingenuity

Barrels do lead to some great ingenuity trying to correct the problems! 

Many people add roofs to try to lessen the leaks that happen during rain and snow.

This first one is my favorite. Very nice looking gazebo to protect their barrel. If, instead of buying the barrel, they’d enclosed that nice gazebo they’d have a much better sauna with more interior room and higher benches. It’d be much more comfortable, less stuffy and more even heat head to toe. But alas, they didn’t know they’d need the gazebo when they bought their barrel.

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This one’s nice too. 

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A couple of sitting boxes on top of the bench along with a couple of different foot boards to try out. 

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Box Chair on top of the bench!

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Stools on top of the bench.

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A twofer: Boxes on top of the bench and they recessed the heater out of the back.

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A vestibule complete with lighting.

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More to come…

 

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* Pathogens, including viruses such as Flu and Covid-19, often spread via droplets in exhaled breath or sneezing. Covid-19 is believed to be able to survive at 75°c for up to 3 minutes, at 65° for up to 5 minutes and 60°c for up to 20 minutes. The survival rate at higher temps is unknown. It is possible that Covid-19 would be killed quickly at higher temps and perhaps quick enough that numerous people in a sauna that is perhaps 95°c at bathers shoulders would have little risk of transmitting it. More: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7372531/, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7372531/