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.
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.
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.