Why does water feel hotter at larger volume? Why does a 104°F pool/tub feel boiling hot, whereas a pot/cup of water at the same temperature does not feel hot at all.
(Normally a pot/cup of water won't be hot enough to cause one to immediately remove ones finger from the water till it's around 165-175°F).
Probably same conductivity, specific heat, BTU's (since the amount of BTU's needed to raise 1°F is proportion to volume of water. Meaning, 1 BTU is needed per pound, so no matter what the volume is it will contain the same BTU's per pound).
Perhaps there's much more "heat" (BTU's/Joules) available in a tub/pool to "refill" the spot which transferred into ones body (perhaps through conductivity) not allowing the area of water touched by ones body in the tub/pool to cool off fast enough.
Another possible factor might be that perhaps there's an increase in convection; not sure if the higher the volume of water, the higher the convection.
 A: It depends on the surface area of your body that is exposed to the hot water. If you get into a hot tub, most of your body is exposed to the heat, whereas dipping your fingers into the water only exposes a small surface area.
The sensitivity of different parts of your body will also play a part. Your fingers and hands are less sensitive to heat than other parts of your body. This also applies to the soles of your feet, where the skin is thicker. Which is why a hot water bottle that feels pleasantly warm under your feet will feel much hotter against your legs. This is also why mothers with young babies are advised to test the temperature of their baby’s bath water with their elbow, which is more sensitive to heat than their hand.
A: The difference in temperature perception between a 104°F pool/tub and a pot/cup of water at the same temperature is likely due to physical phenomenon like thermal mass, convection, heat transfer rate and sensing area (finger vs whole body).
The larger volume of water in a pool or tub means a higher thermal mass that help to maintain the temperature of the water. Also, the surface area of the water in contact with your skin is much larger in a pool or tub than it would be in a cup or pot, allowing for more heat transfer to occur.
Convection is the transfer of heat by the movement of a fluid or gas. In the case of a pool or tub, convection occurs when the warmer water at the surface sinks and is replaced by cooler water from the bottom. This creates a circulating pattern, where warm water is continually brought to the surface and cooled water sinks to the bottom, promoting the transfer of heat throughout the water. This process increases the heat transfer rate to the skin, hence making you feel hot.
In a pot or cup, convection is less likely to occur because the water is confined in a small space, so the heat transfer rate is slower.
