A 45 year engineer clears up electric sauna ventilation | Hacker News Reader

A 45 year engineer clears up electric sauna ventilation

saunatimes.com

203 pointsjmacd68 comments

I enjoy reading articles (even if this one felt like it had been translated slightly clumsily) where scientific rigor has been applied to something mundane.

I've gained an understanding, at least.

The sauna design rabbit hole is a very deep one.

If anyone is interested in more information about sauna design in general, Trumpkin's Notes are by far the most referred to guide out there. [1]

There are also new products [2] which help improve saunas which are not ideally designed or where there are constraints (ceiling height mostly) to deal with.

1: https://localmile.org/trumpkins-notes-on-building-a-sauna/ 2: https://saunum.com/en/

what is some crazy sauna fact?

In Finland sometimes we take advantage of the heat and we cook sausages on our sauna stove by wrapping them in aluminum foil and placing them on the hot rocks. You can still take a sauna normally and afterwards you have a cooked sausage to eat!

Our relatives always had a nice big piece of meat in there when we visited. Ofcourse they had at least three different saunas on the yard. The smoky sauna was mostly used for the cooking.

> Our relatives always had a nice big piece of meat in there when we visited

seems like you and your relatives had a good time ;)

In Korea they cook soy-sauce-marinated eggs

going to give that a try

> can still take a sauna normally and afterwards you have a cooked sausage to eat!

that's what she said

been browsing r/sauna for years in the lead up to building my own sauna. Those trumpkin notes really are the key. It's unfortunate that the sauna industry has very few (if any) DIY kits that follow best practices for traditional saunas

Just looking at those Trumpkin notes for the first time. As a North American, I’m very surprised to see that cedar should not be used. I always thought that was the wood to use for Saunas.

Thanks for the links. I built my own super cheap (under $100) electric sauna, though I would not recommend it for anyone else to copy. It's lasted me about 4 years now though with about every-other-day-usage without burning down the house so... that's nice. I'll see if I can apply any of Trumpkin's Notes to my jank build [0]

[0] https://news.ycombinator.com/item?id=28495062

Thanks for the link. Have recently been looking into saunas. So do you still strap your phone onto a block of ice ?

I’m looking to spend about 1500, if you were to upgrade your situation while having a slightly large shoe string budget, any leads ?

re: ice, yes, though I know Trumpkin and other traditionalists would be appalled. I do (occasionally) practice meditation - but I don't ever want to do it in a sauna.

I have no plans on upgrading so I haven't put any thought into it. A causal search revealed this in your price range [0] but I don't know anything about it. Don't forget that you'll likely need to pay for an electrician to upgrade your home circuit.

For me if I were to upgrade, it would be first be to get a better heater. The thermal foil + sleeping bag is surprisingly effective, though obviously I can't practice Trumpkin's advice on doing hot-cold-hot-cold-hot cycles easily without a door. It currently takes about 10-15m to get up to temp. So if you were on a smaller shoestring budget, I do think my thermal foil + sleeping bag build would save you a _lot_ of money on wood. I built a small (4x4x4) wood cube to sit in (you can see its base in the photo) but it leaked so much air that my DIY heater couldn't keep up. So I went with the thermal foil, which has all kinds of advantages... but it's certainly an eyesore :) A more powerful heater (with the appropriate house circuit) would make a small DIY wood box viable again. I think I _could_ recommend my jank build for others if they used a heater that wasn't DIY.

I still wonder when my DIY heater is going to kill me. I've since covered it with ceramic and wood so I'm no longer worried about 3d degree burns from fainting or whatever. And I use a GFCI outlet so any shock won't kill me. And I literally unplug it when not in use so it won't do anything unexpected. My thermal foil is _flammable_ though... which I found out when my heater started sparking. A better heater won't do that - but still...

Honestly, depending on your situation, it might just be better to save for a "real" sauna. For me time and money are currently at a premium, so I likely won't upgrade for years.

[0] https://se.kristo.shop/products/240064176624-17?variant=4064...

I find it so annoying that you can’t just buy a high quality kit in the USA. It makes no sense to have to design a 1of sauna every time someone wants to build one. Plus sourcing your own material is annoying as well.

I am actually typing this from a sauna with less than ideal ventilation (slightly ajar glass door) - need to cut vent holes to the sauna/house walls but haven’t gotten around to it - so the timing is good. The main use of the ventilation is to not end up with too high CO2 concentration

Wouldn't it be more practical to have a prominent CO2 monitor and only exchange the air (maybe by opening the door for a few seconds) if it CO2 gets too high ?

Maybe it's hard keeping a co2 monitor operating in humid sauna conditions, I dunno.

Also, given that many saunas are not airtight, I wonder what a steady state CO2 concentration would be. It may be high, but not dangerous.

Some additional discussion on Reddit https://www.reddit.com/r/Sauna/comments/1b2skn6/a_45_year_en...

Am I reading this right? Is there no heat exchanger in the ventilation? That seems like an obvious improvement.

The ventilation within the sauna is actually more effective the greater the temperature gradient between the entering low-CO2, cold air and the stale, hot air in the sauna. You want the entering air "falling" on the stove because it's colder i.e. denser than the surrounding air. It then heats up and mixes with the hot air in the sauna.

That being said, almost any real implementation in a cold climate place like Finland would have a heat exchanger at the building level for a mechanized ventilation system. It's of course still not 100% efficient so the circulation system within the sauna still works.

Also to remember is that amount of moisture added in usual sauna session is not insignificant. Throwing at least couple of litres of water on stove is entirely normal in addition to whatever is perspired.

Handling this level of possible condensation might need additional considerations.

What does "at the building level" mean? Is the sauna only part of the building and not the whole building? The article says it's a backyard sauna, which to me sounds like the sauna is the whole building.

Can't speak for this article, but an electric sauna in Finland is almost always inside the building/apartment, accessed via the bathroom. A separate sauna building would have a wood heated stove.

Depending on configuration, either on the apartment unit, single-family house or apartment building level.

As the other commenter said, nowadays sauna in Finland is usually inside your house and the mechanized ventilation is connected to the overall ventilation system of your house. Hence the original article[1] explored the optimal positioning for mechanized air in/outlets in a sauna. The current Finnish building code incorporates the recommendations from this study (as document RT 91-11260).

I guess you could apply the same principles to an electric sauna in a separate building. Just use two fans (one pulling, one pushing) instead of an AC system. Most often a separate sauna building in Finland however has a wood-fired stove, which doesn't need as much consideration for ventilation as an electric sauna. My understanding is that the wood-fired stove itself creates a strong continuous draft which takes care of ventilation in the sauna room (pulling fresh air from outside through the stove and by combustion into the chimney).

[1]: https://publications.vtt.fi/pdf/tiedotteet/1992/T1431.pdf

I'm not really sure what you're critizisng? This was a study done in the early 1990s looking at what would be the best way to build a sauna. This isn't a study in HVAC optimization for a house.

FWIW current finnish building code more-or-less require a heat exchanger in the exhaust air flow. It didn't in 1990.

A sauna is a small, enclosed area with an extremely high moisture content that is only used for short periods of time. The expense of a heat recovery ventilator that could work with this extreme level of moisture wouldn’t even come close to recouping any potential cost savings.

The combination of ventilation and heat source along with water poured on to the source is a way to regulate and adjust the temperature. The goal isn’t to trap as much heat as possible because having some of the heat flow out is key to regulating temperatures.

So, not really an obvious improvement at all.

"The goal isn’t to trap as much heat as possible because having some of the heat flow out is key to regulating temperatures."

Rather to get old air out and fresh one in. Temperature regulation is done by more or less heating, or if all fails, opening the door.

Dry saunas are a thing also. My gym sauna is dry except for the humidity provided by the sweating people sitting in it. They prohibit putting water on the rocks.

Sure but that has very little to do with the Finnish designs of saunas.

Off-topic but I've been curious: how well do phones handle saunas? I thought the heat and moisture would pretty much be the worst environment for electronics. Is that not the case?

Not the one you asked, but I like to sauna in perfectly dry air more than in humidity. Also slightly lower temperature. As there is no humidity, the heat doesn't transfer as quickly. The phone doesn't get hotter than it does on a sunny day outside.

At least in our sauna even in dry air my phone overheats and shuts down.

I read on my iphone’s kindle app in saunas and steam rooms frequently. No problem.

Overheats pretty quickly, especially on the higher bench

For some real numbers:

I have a barrel sauna with a Harvia. I take my phone in all the time. One level only. Where my head is, is where the thermostat is. When the temp says 170F the phone which is maybe a half meter below my head will almost never overheat. At 190F it will overheat eventually. Usually around 15 minutes or so. The higher I hold the phone and the less I insulate it the faster it overheats. “Overheat” in this case simply is the iPhone warning that it is getting too hot. I have the most recent iPhone SE at the time of this writing (2022 iPhone SE)

There’s no danger to the phone whatsoever. The phone is very good about protecting itself. Outside of the heat warnings it cools down and functions normally afterwards. The only real problem is the annoyance of not being able to use the phone in the sauna because Apple is a little overprotective of the device.

There may be no risk to the phone electronics themselves, but you are abusing the battery and increasing the risk of failure though bulging and thermal runaway.

I would personally not call regularly exposing lithium ion cells to 170+ degrees F “safe”.

Why do you think those protections are there?

Thought it would be about heat exchangers.

I have not noticed any venting in the sauna at my gym, but perhaps it's not obvious. It's a pretty big sauna, it will easily seat over a dozen people and people are coming in and out often enough that the door opening probably provides adequate air exchange.

Why is the age of any relevance here?

45 year not 45 years old

Is he 45, or has he been an engineer for 45 years? Either way, I wish I had this guy’s sauna.

If his sauna is the one in the picture, it has a flaw. Benches are placed too low. Your feet should be approximately at the level of the top of the stones. The sauna looks similar to a barrel sauna and they often are too low due to curvature to allow placing benches high enough

Because, he's FORTY FIVE! He's FRAIL with one foot LITERALLY in the GRAVE!! j/k. Someone mentioned that he has 45 years of experience. That makes him closer to 65. If he's still doing cool shit, thats pretty cool.

I wish they'd explain the problem in a short sentence before diving right in. Maybe this blog is for people who already know what the issues with an electric sauna are... bad ventilation, I assume.

If you read the article, the problem is explained quite well:

> In my simple mind, the Finnish Sauna is just a type of Heat Treat Furnace or Oven that you load humans into and try to provide them with three characteristics. (1) not oversaturate their lungs with their own Carbon Dioxide waste products from being enclosed in a sauna with poor ventilation and limited fresh air volume changes (called Air Mixing in the study), (2) create an enjoyable Temperature distribution within the sauna environment (called Temperatures in the study) and lastly (3) provide a well distributed Ladled Steam Humidity cloud throughout the Sauna (called Air Condition in the study). Basically, everything you would expect for a good Finnish Sauna experience.

The rest of the article explains the ventilation needed for this.

That’s not an explanation of the problem though, those are just characteristics of a good sauna.

I don’t see the problem defined well in the article, but it can mostly be surmised from the intro:

> Malcolm has analyzed the Finnish 1992 sauna ventilation study profile, applied his knowledge and experience as a 45 year engineer to test and better understand sauna ventilation in his own backyard sauna.

They wanted to test and understand the sauna ventilation in his backyard sauna and used a 1992 research paper as a reference. I can only assume this venture started because they were dissatisfied with the ventilation in their backyard sauna.

45 year engineer, not 45 year old engineer. It's not about their age but their experience.

The relevance is that someone spent 45 years, as a trained adult engineer no less, not 45 years merely breathing, aware of a problem and only after than much experience, solved it.

It would also be interesting if they had been a 1 year engineer or not an engineer at all, just for different reasons.

what kind of engineer? software engineer? ;D

No a real engineer.

you're tryin to make friends? i'd be a little careful around here

I'm not to worried. ;-) My friends don't have ego problems.

dude, I'm just trying to help you

dude, thanks.

Fwiw it didn't read naturally to me either. I suppose I'd say 'an engineer of [or 'for'] 45 years'. Or 'Malcolm, 45 years an engineer, [...]'.

In what part of the world is it typical to say "45 year engineer"? I'm an engineer in the western US, and would say "an engineer with 45 years of experience". I interact with lotsa international english; this one is new

I have definitely seen that before. In any case, despite the website being owned by an American, the language is not common American English:

> He is enjoying his sauna 4-6 times a week. Instead of watching the “idiot TV”, Malcolm has spent his evening watching his thermal meters in his hot room.

One would not use the present continuous tense in that context as much as in that sentence.

The words are the words. No one else can help the fact that you interpret words that weren't either written or implied.

A 10 year smoker may or may not also be a 10 year old smoker, but probably not.

A 6 month project may or may not also be a 6 month old project. Etc etc.

tldr: place air inlet above the heat (B); air outlet on the other side at the floor (D). See figure: https://www.saunatimes.com/wp-content/uploads/IMG_6556-1-560...

This ensures: 1) quick heat up of fresh air 2) vertically uniform heat 3) creation of better steam

I wonder if this holds true for a wood burning sauna too? An active fire in the stove creates a massive draft that'll pull air through the stove and out the chimney.

Where I live, saunas have the stove’s inlet outside the sauna itself.

Yeah the only way for wood stoves to work ~decently in a small room like that is to be direct vented.

No it's different for wood burning when inside the space because they act as an effective exhaust on their own.

http://localmile.org/proper-ventilation-for-electrically-hea...

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