When trying to understand the three types of heat transfer, it is easy to get lost in the weeds, but could there be a perfect mix, much like with a jazz trio?
As we enter the jazz club, we see drums, bass, and piano onstage. The musicians haven’t arrived yet. Similarly, as we light our sauna stoves, we begin the process of igniting our own jazz trio of heat transfer. The match lights the kindling. Then, the kindling lights the fire. From here, you can see how heat transfers:
The three types of heat transfer.
Guest post collaboration: I am pleased to introduce Grant Whittle who is one of the most thoughtful, insightful, reflective sauna thinkers I know. (and I seem know a ton!). Grant’s schooling is in Environmental Science and Engineering and he practices in the civil engineering field. He regularly works with steam and thermal energy flow. By day. Grant’s direct input is in italics. Welcome Grant!
Drums and radiant heat transfer
Have you ever been to a concert for the sound check? With every bang of the snare drum, the technicians are mixing how much snare drum is in the room to keep it from being too harsh. It is similar to adjusting for the right amount of radiant heat transfer. Radiant heat transfer is the heat you feel, for example, from the sun on your back. Such radiant heat penetrates deeply into your body. In a sauna, radiant heat transfer from the first to the sauna stove and then to the room. is the source of all heat you feel throughout the sauna.
Often, the technicians setting the stage for a Jazz Trio will position the drummer behind an acoustic shield to direct and buffer the harshness of the drums and to maintain better acoustic balance for the audience. Good sauna stove design will likewise shield and direct the radiant heat for the greater enjoyments of those on the benches.
This radiant heat transfer, like sun on our backs, feels great. But too much and ouch, just like too loud drums at a concert.
Over the top pounding drum of radiant heat transfer is what we feel in a barrel sauna, while sitting too close to a toaster oven style heater/stove. It is said that in barrel saunas, the reason why there are benches on both sides is so that halfway through your sauna round, you can switch sides to even out the roasting. Like a hot dog on a grill.
Pre-heating
This will also be the case with any sauna when you don’t pre-heat the hot room’s wood mass long enough so that the only radiant heat in the room is coming unidirectionally from the stove. Furthermore, the tin, uninsulated wood of a barrel can never radiate much heat back into the hot room anyway: the little heat the barrel walls are radiating is mostly leaving out into the world.
Radiant heat transfer is a great thing in sauna, like drums are a great thing at a concert. Have you ever been in a house with radiant heat? It’s a different kind of heat vs. the warm air flow circulating from ducts. Radiant heat provides more even heat throughout the room. A good sauna allows for heat to gently radiate from every surface surrounding the bathers: the benches, the walls, the ceiling, the rocks. And a good sauna technician will shield the patrons from the harshest radiant heat so that it doesn’t come directly from the steel of the stove. As we listen to music, consider how the drums hit us: the beat, the high hat, the bass drum. Direct impressions to carry the tune. Without the drums (the radiant heat of the sauna), the music is flat. It doesn’t penetrate you. It is only skin deep, just like hot convective airflow by itself.
Bass and conductive heat transfer
Have you ever been to a concert and observed the interaction between drummer and bass player? This is similar to how radiant partners with conduction. In a wood fired sauna stove, the radiant heat from a fire in the firebox transfers into the metal and then from the metal to the rocks primarily by conduction. Likewise, in an electric heated sauna stove, the heat from the elements conducts into the rocks. Sauna rocks store this heat and radiate it more slowly, less harshly than steel. A good mass of rocks gives lots of latent heat storage that can be conducted rapidly to water poured over them.
Have you been to a reggae concert at Red Rocks? Have you ever felt the heat of the music deep into your core? Next time, instead of yelling out “irie, ya mon!” try yelling out “lämpömassa, ya mon!” and see if any other sauna enthusiasts turn their heads with a smile and a thumbs up. (As sauna becomes more popular, the odds of this happening are increasing).
All work and no play makes jack a dull boy. All drums and no bass make music dull and unlistenable. And, all radiant and no conduction makes a sauna feel like a toaster oven. The bagel browns but the inside is still frozen. Why do chefs use only gas stoves and cast-iron frying pans? Easy answer, explained here. But for now, we are at the mixing board, mixing drum and bass. Those who feel it, knows it. Even if they don’t fully understand and can’t properly express the theory behind it.
Good heat is egalitarian and responds equally to all thermal heat education status.
Piano and convective heat transfer
Once the levels of drum and bass are set, the technicians turn to the lead instrument. Within our metaphor, the lead instrument is the piano. The piano carries the tune. The piano leads the other instruments. Too much piano, and it’s just piano. Too little piano and the music has little ability to stir our emotions. On the sauna bench, convective heat transfer is the heat we feel through air movement. Good ventilation isn’t just the source for pedantic chatter on social media. Ventilation not only provides critical fresh air and oxygen in our hot rooms, but it helps move the hot air for more even heating of the room.
Often, breaking a sweat in a lame ass health club sauna takes too long because of poor ventilation. Convective heat transfer is what we feel when you blow air on your skin as you sit on the sauna bench. The right air movement in a sauna contributes to a sauna feeling hotter; the right kinds of heat transfer. The movement of good heat through the room. Then, the circulation of the heat radiating and conducting from the source of heat in our sauna: the stove.
At the jazz club, the piano is helping carry and move the tune.
Working together
Imagine the jazz trio working together. Think about the harmony, the melody, the synergy of all instruments helping create beautiful music. This is the vibe in our saunas. Good saunas. The jazz trio of heat transfer, three instruments (radiant, conductive, and convective heat) working together to create good sauna
We feel this complexity of heat transfer through the löyly convecting (piano) throughout the room, through the heat radiating (drums) from the walls deeply into our body core, and through the heat conducting (bass) to our skin from the benches. All together, the jazz trio makes for gently enveloping, yet intense heat. This complex “music” of the Jazz Trio of sauna is what the Finnish refer to as lämpömassa. You can’t achieve lämpömassa without a proper balance across the jazz trio playing with and off each other.
When you feel good heat, it’s all over. Just like listening to a perfectly tuned jazz trio, we can create a perfectly tuned sauna. When we choose the right sauna stove and build the right sauna, we are our own producers. We are tuning the three types of heat transfer (radiant, conductive, convection). Benches, walls, stove surround. All the sauna design choices conductive material that helps to envelope us with the lämpömassa heat, just like at a good jazz club. Drum, bass and piano balanced by the technicians to work with the room design. Here is where different technicians argue about the importance of insulation, heat shielding, and thicker wall paneling, but that’s another subject.
Why is good heat important?
When you feel good heat, it’s all over. When we feel good heat, we enjoy our time on the sauna bench. We heat our bodies completely, thoroughly and yet both gently & intensely at the same time. This is lämpömassa. This is good sauna, and good sauna is available to all of us.
6 thoughts on “The jazz trio of heat transfer: is there a perfect mix?”
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My medium Kuuma stove is the giant subwoofer in my sauna. Firebrick and lots of rocks drum up lots of heat to the walls and benches and even my crocs sitting on the floor near the door. Pouring water on the rocks repeatedly provides wonderful improvisational solos that you can feel skin deep, like Les McCann and Eddie Harris breaking loose on Compared to What.
More from Grant:
This is more golden nugget explanation from Grant:
“almost the entirety of the dominant “modern” Finnish sauna design is for mass export sales purposes.
A lot of “traditional” Finnish sauna design was left behind for this commercial export goal.
“Traditional” Finnish Sauna Design had:
Higher wood mass for more enveloping mass radiant heat around the bather.
“Modern” Finnish export sauna design is based upon thin wood cladding to limit the mass that has to be heated before the air will warm up. (Necessary because of changes in stove design to make shipping more affordable.)
“Traditional” Finnish Sauna Design relies on:
High mass rock fireplaces (original savusauna), then high mass iron stoves, & then high mass steel stoves. The point radiant of each has to either be far away from the bather and the fire (source of point radiant) is typically stopped or dampered down before and the point radiant often shielded once bathers enter. The high “point radiant” during heat up results in faster heating of more wood mass, for subsequent greater gentle radiant heat on the bathers from the surrounding wood.
“Modern” Finnish Sauna Design relies on:
A lower steel mass that doesn’t point radiate for as long after bathers enter and after the fire or the electricity is lowered… This lets bathers sit closer to the stove in a smaller sauna size (ideal for the urban usage case and mass export). Much lower point radiant and much lower wood mass allows more of the comparatively limited thermal energy to heat the air and to drive convective airflow. Less mass to heat thereby drives faster air heat up. But the comparative lack of point radiant during heat up results in very little radiant absorbed by the lower mass of wood in the thinly clad walls. This lack of radiant heat from the wood wall mass significantly alters the “feel” of the heat. Convective and conductive heat tend to be concentrated “skin deep” heat. The deeper penetrating radiant heat required for traditional “lampomassa” is missed.”
And even more golden Grant Nuggets:
“I agree that sauna designers have to intentionally balance the heat input of radiant & conductive heat.
The convective airflow design also plays a critical role in the conductive heat flow into the surface of the mass of the room including the people.
Good sauna “composition” is very much analogous to a good Jazz Composition with a Jazz Trio.
And details like the acoustic shield needed for drums to keep them from being overwhelming is perfectly analogous in my mind to the radiant heat shielding desirable (after bathers enter) with sauna stoves.
I am eventually going to publish a follow-up version about Sauna Jazz that I wrote which further deep dives into the Jazz comparison… and gets into some SERIOUS Jazz composition theory. (I played trombone in my youth and loved Jazz music.) Glenn was a genius to come up with this analogy and I decided to run even further with it…
That depends both on what you enjoy as a bather and on the “stages” of sauna operation.
During sauna hot room heat up, you “need” intense radiant towards the wood walls and benches, if you enjoy the gentle radiant heat coming out of the wood mass when you enter to bathe.
If you don’t enjoy unidirectional, intense radiant heat from the stove and stove rocks while bathing, then the radiant heat so critical for shorter heat up times needs to be shielded before bathers enter.
Having a stove that “can’t” radiate heat into the walls and benches means that your sauna will primarily only employ convective heat against your skin surface. You will miss out on deeply penetrating but gentle radiant heat from the wood mass while bathing.
So… I want to maximize radiant heat output from the stove during pre-heating (for radiant infusing of the wood surround), but minimize radiant heat output during bathing by dampering the air intake to lower radiant production by the stove, combined with the availability of added radiant shielding for use when bathers enter.
Rocks on the sides of the stoves will radiate much longer than steel, due to their high thermal mass and co.comparatively slower rate.of radiation) after the fire has been dampered… but fully saturated rock radiant can still be uncomfortably high for many bathers. Once again, available shielding to protect bathers is advisable in my opinion.
What I don’t want is a stove incapable of outputting high radiant during heat up. A stone surround would cause such an issue. Too aggressive of heat shielding usage during heat up would cause that issue. The result is minimal radiant available to the bather from the wood… Not ideal.
You MUST have high radiant from the stove directed at the benches during heat up, if the bather is going to enjoy gentle radiant from the wood while sauna bathing.”
And Grant doesn’t stop there:
“Ceiling height is just another compromise likely made for mass export sales. With lower wood mass, insulation also became more critical in cold climates. Lower air volume per person required much better ventillation design.
The modern insulation and modern ventillation aspects improve (not compromise) the performance so I am good with those. The modern fire safety aspects of thermal shielding and clearances are also worthy improvements that don’t lower sauna performance on any way.
But as I understand it, “traditional” sauna lampomassa requires a carefully composed balance of radiant, conductive, and convective heat — What Glenn Auerbach is calling the “Jazz Trio of Heat.” You can’t get that from “modern,” mass export Finnish Sauna Design. It REQUIRES the kind of “traditional” stoves and more traditional hot room designs that have remained prevalent among Finnish Americans in the Great Lakes region and in rural Finland…
That “traditional” sauna practice seems to be better preserved in the remote parts of Finland and in the isolated Finnish American communities than it is across Finland as a whole. Such “traditional” Finnish sauna is certainly not reflected in the mass market exports coming out of Finland today…
Those who want exceptional lampomassa turn to the actual “traditional” ways of designing a sauna. Those who need to force a sauna to work in the less than ideal requirements of an urban setting… they have to make compromises and accept “modern” Finnish Sauna design accommodated to such circumstances.
Most consumers live in urban settings… The mass market demand is for “modern” urban saunas. IR Therapy Chambers takes that “mass market” demand even further away from “traditional” Finnish sauna — so far away that it should not even be called sauna.
But ONLY traditional sauna design balancing radiant, conductive, and convective heat (The Jazz Trio of Heat) actually provides lampomassa… I am absolutely convinced of this.
You won’t feel the heat gently, but deeply & intensely into your core without a significant radiant mass component in the sauna design. And you won’t feel gentle (or “soft” as the Finns call it) loyly without superheated rocks to flash “drier” steam. [There is good reason why Finns call saunas with good loyly “dry.”] Lower temperature rocks don’t conduct enough thermal energy into the water molecules to separate them as far. This results in a less favorable dewpoint and “harsher” steam that conducts more heat into your skin faster because of the higher density of water molecules across your skin surface.
Good lampomassa and good loyly REQUIRE the ages old wisdom behind “traditional” Finnish sauna design.
These “modern” sauna designs with their compromises made for mass urban usage are like McDonald’s burgers. They satisfy your craving cheaply, but no one would mistake them for a “real” quality hamburger.“
Terrific analogy for the different modes of heat transport and nice insight into how to manage the three modes in design and practice.
Lewis: we would be best chatting on this while sipping a Jamaican rum between rounds or a real ale after sauna at your local pub, as I’m aligned with where your head is at. As we know, temperature is one measure of hot room climate. It’s a linear gig that can be satisfied with thin metal and heat shields and a convective loop whoo hoo. Check mark there. Yet, let’s imagine another gauge on the wall: a Lämpömassa meter. When we can add this measure to help define our sauna climate, like a music producer dialing his mixing board, we are then tuning into the jazz trio. Give me a sauna stove where I can dial up Robbie Shakespeare’s bass, please. The piano is too loud and only playing around my skin. Let’s tune the mix of the three methods of heat transfer. Can we feel it in our bones?