Sauna: Wood does not feel so hot












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When you go to the sauna you may sit in a room with 90°C+. If it is a "commercial" sauna it will be on for the whole day. How does it come that when you sit on the wood you don't get burned?



I believe this question is different than the "classical" one concerning the "feeling" of heat, which may be explained with a low heat transfer. After a much shorter time other objects seem much "hotter", and the heat transfer is not different (as it's still a room filled with the same air).



My guess would be that the reason is the heat capacity but I cannot really explain it. In my understanding a capacity is the ability to store something (heat, charge, ...). Why should an object be cooler if it can store less heat? Also, cannot this be ignored in this case, as the wood is exposed to the temperature for a very long time?






thermodynamics







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    $begingroup$


    When you go to the sauna you may sit in a room with 90°C+. If it is a "commercial" sauna it will be on for the whole day. How does it come that when you sit on the wood you don't get burned?



    I believe this question is different than the "classical" one concerning the "feeling" of heat, which may be explained with a low heat transfer. After a much shorter time other objects seem much "hotter", and the heat transfer is not different (as it's still a room filled with the same air).



    My guess would be that the reason is the heat capacity but I cannot really explain it. In my understanding a capacity is the ability to store something (heat, charge, ...). Why should an object be cooler if it can store less heat? Also, cannot this be ignored in this case, as the wood is exposed to the temperature for a very long time?






    thermodynamics







    share|cite|improve this question









    $endgroup$















      2












      2








      2





      $begingroup$


      When you go to the sauna you may sit in a room with 90°C+. If it is a "commercial" sauna it will be on for the whole day. How does it come that when you sit on the wood you don't get burned?



      I believe this question is different than the "classical" one concerning the "feeling" of heat, which may be explained with a low heat transfer. After a much shorter time other objects seem much "hotter", and the heat transfer is not different (as it's still a room filled with the same air).



      My guess would be that the reason is the heat capacity but I cannot really explain it. In my understanding a capacity is the ability to store something (heat, charge, ...). Why should an object be cooler if it can store less heat? Also, cannot this be ignored in this case, as the wood is exposed to the temperature for a very long time?






      thermodynamics







      share|cite|improve this question









      $endgroup$




      When you go to the sauna you may sit in a room with 90°C+. If it is a "commercial" sauna it will be on for the whole day. How does it come that when you sit on the wood you don't get burned?



      I believe this question is different than the "classical" one concerning the "feeling" of heat, which may be explained with a low heat transfer. After a much shorter time other objects seem much "hotter", and the heat transfer is not different (as it's still a room filled with the same air).



      My guess would be that the reason is the heat capacity but I cannot really explain it. In my understanding a capacity is the ability to store something (heat, charge, ...). Why should an object be cooler if it can store less heat? Also, cannot this be ignored in this case, as the wood is exposed to the temperature for a very long time?






      thermodynamics




      thermodynamics






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      asked 2 hours ago









      famfopfamfop

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          2 Answers
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          $begingroup$

          First of all, I hope you sit on a towel. But even when you touch wood with your bare skin, you don't get burned. This indeed has to do with thermal conductance.



          The point is not the heat transfer between the wood and your skin, but rather the heat flowing within the wood. When you touch the surface, your skin and the wood at the very surface equalize their temperature. But because it's only a thin film of wood at the surface, not much heat is transferred. To further heat up your skin, heat from deeper down in the wood needs to get to the surface, so it can be transferred to your skin. This is the process that is slow whenever a material has low heat conductance, like wood.



          Compare this to touching metal, where the heat stored deep in the bulk of the material can rush to the surface rather quickly, if something cool is touching the surface. Much more heat is transferred and you will burn your hand.



          The low heat capacity of a wooden bench certainly also plays a role, simply because if there's little heat stored in the material, it has less energy to heat up your skin with.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Ok this makes sense. So if I had a material with a(n extremely) high heat capacity but a low heat transfer I would still get burned, as the thin film could theoretically store enough heat already?
            $endgroup$
            – famfop
            2 hours ago








          • 1




            $begingroup$
            It is a combination of the two, but in principle yes. If the region at the surface that can transfer its heat relatively quickly to your skin has a lot of energy stored up, it will still burn you.
            $endgroup$
            – noah
            2 hours ago



















          -1












          $begingroup$

          Wood is a poor conductor of heat. The thermal conductivity of wood is relatively low because of the porosity of timber. Thermal conductivity declines as the density of the wood decreases. ... For example, the thermal conductivity of pine in the direction of the grain is 0.22 W/moC, and perpendicular to the grain 0.14 W/moC



          Wood across the grain, white pine 0.12

          Wood across the grain, balsa 0.055

          Wood across the grain, yellow pine, timber 0.147

          Wood, oak 0.17

          Wool, felt 0.07

          Wood wool, slab 0.1 - 0.15
          (https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html)






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Thanks for the answer but actually it does not really answer the question. I know the thermal conductivity is low but the question is more about why I don't get burned.
            $endgroup$
            – famfop
            2 hours ago











          Your Answer





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          2 Answers
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          2 Answers
          2






          active

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          active

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          active

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          5












          $begingroup$

          First of all, I hope you sit on a towel. But even when you touch wood with your bare skin, you don't get burned. This indeed has to do with thermal conductance.



          The point is not the heat transfer between the wood and your skin, but rather the heat flowing within the wood. When you touch the surface, your skin and the wood at the very surface equalize their temperature. But because it's only a thin film of wood at the surface, not much heat is transferred. To further heat up your skin, heat from deeper down in the wood needs to get to the surface, so it can be transferred to your skin. This is the process that is slow whenever a material has low heat conductance, like wood.



          Compare this to touching metal, where the heat stored deep in the bulk of the material can rush to the surface rather quickly, if something cool is touching the surface. Much more heat is transferred and you will burn your hand.



          The low heat capacity of a wooden bench certainly also plays a role, simply because if there's little heat stored in the material, it has less energy to heat up your skin with.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Ok this makes sense. So if I had a material with a(n extremely) high heat capacity but a low heat transfer I would still get burned, as the thin film could theoretically store enough heat already?
            $endgroup$
            – famfop
            2 hours ago








          • 1




            $begingroup$
            It is a combination of the two, but in principle yes. If the region at the surface that can transfer its heat relatively quickly to your skin has a lot of energy stored up, it will still burn you.
            $endgroup$
            – noah
            2 hours ago
















          5












          $begingroup$

          First of all, I hope you sit on a towel. But even when you touch wood with your bare skin, you don't get burned. This indeed has to do with thermal conductance.



          The point is not the heat transfer between the wood and your skin, but rather the heat flowing within the wood. When you touch the surface, your skin and the wood at the very surface equalize their temperature. But because it's only a thin film of wood at the surface, not much heat is transferred. To further heat up your skin, heat from deeper down in the wood needs to get to the surface, so it can be transferred to your skin. This is the process that is slow whenever a material has low heat conductance, like wood.



          Compare this to touching metal, where the heat stored deep in the bulk of the material can rush to the surface rather quickly, if something cool is touching the surface. Much more heat is transferred and you will burn your hand.



          The low heat capacity of a wooden bench certainly also plays a role, simply because if there's little heat stored in the material, it has less energy to heat up your skin with.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Ok this makes sense. So if I had a material with a(n extremely) high heat capacity but a low heat transfer I would still get burned, as the thin film could theoretically store enough heat already?
            $endgroup$
            – famfop
            2 hours ago








          • 1




            $begingroup$
            It is a combination of the two, but in principle yes. If the region at the surface that can transfer its heat relatively quickly to your skin has a lot of energy stored up, it will still burn you.
            $endgroup$
            – noah
            2 hours ago














          5












          5








          5





          $begingroup$

          First of all, I hope you sit on a towel. But even when you touch wood with your bare skin, you don't get burned. This indeed has to do with thermal conductance.



          The point is not the heat transfer between the wood and your skin, but rather the heat flowing within the wood. When you touch the surface, your skin and the wood at the very surface equalize their temperature. But because it's only a thin film of wood at the surface, not much heat is transferred. To further heat up your skin, heat from deeper down in the wood needs to get to the surface, so it can be transferred to your skin. This is the process that is slow whenever a material has low heat conductance, like wood.



          Compare this to touching metal, where the heat stored deep in the bulk of the material can rush to the surface rather quickly, if something cool is touching the surface. Much more heat is transferred and you will burn your hand.



          The low heat capacity of a wooden bench certainly also plays a role, simply because if there's little heat stored in the material, it has less energy to heat up your skin with.






          share|cite|improve this answer









          $endgroup$



          First of all, I hope you sit on a towel. But even when you touch wood with your bare skin, you don't get burned. This indeed has to do with thermal conductance.



          The point is not the heat transfer between the wood and your skin, but rather the heat flowing within the wood. When you touch the surface, your skin and the wood at the very surface equalize their temperature. But because it's only a thin film of wood at the surface, not much heat is transferred. To further heat up your skin, heat from deeper down in the wood needs to get to the surface, so it can be transferred to your skin. This is the process that is slow whenever a material has low heat conductance, like wood.



          Compare this to touching metal, where the heat stored deep in the bulk of the material can rush to the surface rather quickly, if something cool is touching the surface. Much more heat is transferred and you will burn your hand.



          The low heat capacity of a wooden bench certainly also plays a role, simply because if there's little heat stored in the material, it has less energy to heat up your skin with.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered 2 hours ago









          noahnoah

          3,146824




          3,146824












          • $begingroup$
            Ok this makes sense. So if I had a material with a(n extremely) high heat capacity but a low heat transfer I would still get burned, as the thin film could theoretically store enough heat already?
            $endgroup$
            – famfop
            2 hours ago








          • 1




            $begingroup$
            It is a combination of the two, but in principle yes. If the region at the surface that can transfer its heat relatively quickly to your skin has a lot of energy stored up, it will still burn you.
            $endgroup$
            – noah
            2 hours ago


















          • $begingroup$
            Ok this makes sense. So if I had a material with a(n extremely) high heat capacity but a low heat transfer I would still get burned, as the thin film could theoretically store enough heat already?
            $endgroup$
            – famfop
            2 hours ago








          • 1




            $begingroup$
            It is a combination of the two, but in principle yes. If the region at the surface that can transfer its heat relatively quickly to your skin has a lot of energy stored up, it will still burn you.
            $endgroup$
            – noah
            2 hours ago
















          $begingroup$
          Ok this makes sense. So if I had a material with a(n extremely) high heat capacity but a low heat transfer I would still get burned, as the thin film could theoretically store enough heat already?
          $endgroup$
          – famfop
          2 hours ago






          $begingroup$
          Ok this makes sense. So if I had a material with a(n extremely) high heat capacity but a low heat transfer I would still get burned, as the thin film could theoretically store enough heat already?
          $endgroup$
          – famfop
          2 hours ago






          1




          1




          $begingroup$
          It is a combination of the two, but in principle yes. If the region at the surface that can transfer its heat relatively quickly to your skin has a lot of energy stored up, it will still burn you.
          $endgroup$
          – noah
          2 hours ago




          $begingroup$
          It is a combination of the two, but in principle yes. If the region at the surface that can transfer its heat relatively quickly to your skin has a lot of energy stored up, it will still burn you.
          $endgroup$
          – noah
          2 hours ago











          -1












          $begingroup$

          Wood is a poor conductor of heat. The thermal conductivity of wood is relatively low because of the porosity of timber. Thermal conductivity declines as the density of the wood decreases. ... For example, the thermal conductivity of pine in the direction of the grain is 0.22 W/moC, and perpendicular to the grain 0.14 W/moC



          Wood across the grain, white pine 0.12

          Wood across the grain, balsa 0.055

          Wood across the grain, yellow pine, timber 0.147

          Wood, oak 0.17

          Wool, felt 0.07

          Wood wool, slab 0.1 - 0.15
          (https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html)






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Thanks for the answer but actually it does not really answer the question. I know the thermal conductivity is low but the question is more about why I don't get burned.
            $endgroup$
            – famfop
            2 hours ago
















          -1












          $begingroup$

          Wood is a poor conductor of heat. The thermal conductivity of wood is relatively low because of the porosity of timber. Thermal conductivity declines as the density of the wood decreases. ... For example, the thermal conductivity of pine in the direction of the grain is 0.22 W/moC, and perpendicular to the grain 0.14 W/moC



          Wood across the grain, white pine 0.12

          Wood across the grain, balsa 0.055

          Wood across the grain, yellow pine, timber 0.147

          Wood, oak 0.17

          Wool, felt 0.07

          Wood wool, slab 0.1 - 0.15
          (https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html)






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Thanks for the answer but actually it does not really answer the question. I know the thermal conductivity is low but the question is more about why I don't get burned.
            $endgroup$
            – famfop
            2 hours ago














          -1












          -1








          -1





          $begingroup$

          Wood is a poor conductor of heat. The thermal conductivity of wood is relatively low because of the porosity of timber. Thermal conductivity declines as the density of the wood decreases. ... For example, the thermal conductivity of pine in the direction of the grain is 0.22 W/moC, and perpendicular to the grain 0.14 W/moC



          Wood across the grain, white pine 0.12

          Wood across the grain, balsa 0.055

          Wood across the grain, yellow pine, timber 0.147

          Wood, oak 0.17

          Wool, felt 0.07

          Wood wool, slab 0.1 - 0.15
          (https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html)






          share|cite|improve this answer









          $endgroup$



          Wood is a poor conductor of heat. The thermal conductivity of wood is relatively low because of the porosity of timber. Thermal conductivity declines as the density of the wood decreases. ... For example, the thermal conductivity of pine in the direction of the grain is 0.22 W/moC, and perpendicular to the grain 0.14 W/moC



          Wood across the grain, white pine 0.12

          Wood across the grain, balsa 0.055

          Wood across the grain, yellow pine, timber 0.147

          Wood, oak 0.17

          Wool, felt 0.07

          Wood wool, slab 0.1 - 0.15
          (https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html)







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered 2 hours ago









          RickRick

          2358




          2358












          • $begingroup$
            Thanks for the answer but actually it does not really answer the question. I know the thermal conductivity is low but the question is more about why I don't get burned.
            $endgroup$
            – famfop
            2 hours ago


















          • $begingroup$
            Thanks for the answer but actually it does not really answer the question. I know the thermal conductivity is low but the question is more about why I don't get burned.
            $endgroup$
            – famfop
            2 hours ago
















          $begingroup$
          Thanks for the answer but actually it does not really answer the question. I know the thermal conductivity is low but the question is more about why I don't get burned.
          $endgroup$
          – famfop
          2 hours ago




          $begingroup$
          Thanks for the answer but actually it does not really answer the question. I know the thermal conductivity is low but the question is more about why I don't get burned.
          $endgroup$
          – famfop
          2 hours ago


















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