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Sweating at different rates, surface blood vessel dilation including in your lungs, all change the flux. Having longer hair or wearing warmer clothing can too and can be balanced by those other things. Activity also gets balanced by those things. Eating cold food and drink vs warm etc.

That we maintain a baseline temperature doesn't tell you that metabolism alone is all that regulates it, there are other factors.

Your body can change the temperature gradient near its surface to retain or expel heat without a change in metabolism.

metabolism varies greatly controlling for height, activity level, and weight . sometimes as much as 600 kcal /day

"Humans are spherical cows"