This notion is a concept to address several problems with existing gameplay:
1. Heat is useless with fully upgraded gear. A player who opens a treasure box with heat has "lost" compared to a treasure box with crowns.
2. UVs are akin to gambling in terms of acquisition and the "jackpot" of Very High or Maximum.
3. The gulf between 5-star max heat gear and 5-star max heat gear with 3 highest value UVs can only be crossed via random investment. This is dissuading both to FtP and PtP players, as the investment is uncertain.
Let the gremlins or Boost sell "Heat Tanks" (not sure if these should cost cr or CE). These tanks would occupy a trinket slot (thereby still requiring a CE investment), and would fill if none of your other gear needed heating. Once full, these tanks could be used by the gremlins to upgrade a single UV, requiring more tanks to upgrade at the higher levels. For example, to upgrade a UV from Low to Medium might cost 1 Heat Tank, while upgrading a UV from Ultra to Maximum would cost 16 tanks.
Tweakable variables:
How much should Heat Tanks cost?
How much heat should it take to fill a Heat Tank?
How many Heat Tanks should each level of upgrading cost?
i feel you should be able to sell heat at end of stage for like a 3 heat to 1 crown racieo like there is a option to "sell heat" and a "use heat" option at end of level this would make the issue of unused heat and help newer players farm that needed crowns to get the next gear set. you could work this into some sorta trinket like a "heat compressor" that stores heat and terns it into "intense heat" i more powerful heat that would be worth more , it would be 5 heat for 1 "intense heat" being worth 6 normal heat.