Very hastily created thermomancy magic system

Howdy! I was working on a world building project when I stumbled across this sub and thought I’d write down my ideas for a magic system.

The main magic system in the world I have revolves around manipulating the temperatures of the things around you, this is one of the main ways humans have survived as the world is set in an intense ice age. The rules of thermomancy goes as follows:

• Normal people cannot access thermomancy, one must first drink a liquid known as Holy Marrow in order to be able to access it
• Thermomancers have to drain heat from their environment in order to dispense it back out (in an equivalent exchange kind of relationship). In doing so, the Thermomancer acts as a kind of cable for heat as they cast their spells. Stronger thermomancers are more resistant to heat than beginners, and any beginner who tries to cast high level thermomancy would probably burst into flames
• Thermomancers can drain heat from their environment in the nearby space around them, they don’t need to directly be in contact with where they get their heat from, just kind of close
• It gets harder and harder to take the heat from a space as it gets colder. For example, no Thermomancer can drain so much heat from a space that it reaches absolute zero, but extremely high level mages can get close
• Using thermomancy can be made slightly easier if you physically move your body when you intend to cast something (like firebending in avatar)
• Thermomancy affects only the strict temperature, if you want to cast fireball, you’ll first need something that you can light on fire
• Thermomancers can sacrifice some heat in order to have limited amount of control over the movement of what they heated up. For example, your fireball might not be as hot but now it’s flying at your enemies

The main application of thermomancy is pyromancy and just generally keeping people warm in the freezing temperatures. There are specializations of the art in areas such as combustion / explosion magic, steam, and metalwork. High level thermomancers can also do cryomancy by applying the principles in reverse.