[scientizscht (OP)]

What is the minimum wattage of a heater placed on your skin that you can feel?

Many thanks!

[chiralSPO]

As I understand it, our skin is better at discerning temperature difference than wattage. A small droplet of hot water landing on the skin may only deliver heat energy at a rate of 3 or 4 watts, but you will definitely feel it!

[alancalverd]

Zero! In a normal ambient at less than 30°C your skin radiates convects and evaporates heat away from your body. You need to lose around 50 - 100W to maintain your core temperature within viable limits. If you cover one hand with a glove, so you are losing 1 or 2W less from that hand, you will notice the difference in a few seconds.