# Which one conducts heat better: water, or air?

If we were to assume room conditions (20°C @ 100 kPa), which of the fluids conducts heat better, and why?

• Water. By a lot. Commented Jan 30, 2014 at 7:06
• Which of the fluids? Do you assume pressure high enough for air to be fluid in 20C? Commented Jun 17, 2015 at 9:33
• "Fluid" includes gases and even particulate solids that can "flow". Just look up "fluid physics".
– nasu
Commented Sep 8, 2022 at 11:43

Clicking on the first link in a quick google search for thermal conductivity of common materials takes you to the engineering toolbox. There you will find that the thermal conductivity of air is $0.024\frac{W}{m K}$ and that the thermal conductivity of water is $0.58\frac{W}{m K}$. So, water conducts heat more than twenty times as well as air.

• Just to add to this, in general, liquids virtually always conduct heat better than gases, primarily because they have higher densities. Commented Jan 30, 2014 at 3:06
• Not just twice as well, but more than twenty times better. Commented Jan 30, 2014 at 3:16
• @Hans-PeterE.Kristiansen Oops. Corrected. Commented Jan 30, 2014 at 3:20
• @DumpsterDoofus -What is the relation between density of a substance and its thermal conductivity?
– SRS
Commented Mar 4, 2014 at 17:41
• @Roopam: For fluids (such as air or water), higher density typically means higher volumetric heat capacity, which typically means higher heat transfer per volume of fluid convected across the object surface. Commented Mar 4, 2014 at 17:46

Going a bit beyond the initial question of thermal conductivity, also consider the fact that air can transfer heat by convection. As air heats, it expands, rises and is replaced by cooler air. I don't believe water convects much at all. Why? because it does not expand when heated, and therefore its cooling is limited to conduction (if not being pumped). Just something to think about.

• Welcome to PSE! This is a question-answer site focused on physics. New users are always welcome. The answer you have given doesn't seem like an answer but more likely a comment. When you will have enough reputation, you can comment on such posts everywhere. But for now please wait for a while. You can edit this post in such a way that clearly answer the question. Commented Sep 8, 2022 at 5:13
• This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review Commented Sep 8, 2022 at 8:04