How would you show that heat is produced during respiration?

Well, honey, when you're breaking down those macronutrients during respiration, your body is like a little furnace, producing heat as a byproduct. You can measure this heat production using a calorimeter, which basically tells you how much energy is being released during the process. So, yeah, next time someone asks you why you're hot stuff, you can tell them it's just your cells working hard during respiration.