"The latest trend in energy production: Coal! Because global warming is a hoax. (Level One)"
"As it turns out, if you throw enough money at it, coal can be pretty clean. (Level Two)"
The Coal Reactor is a starbux or tournament acquired room that provides extra power to your ship. It's incredibly small and only provides two power when upgraded so it might not seem very useful at first. The Coal Reactor is mostly for end game to power the very heavy power consuming ships.
Just like the Small Reactor and Fusion Reactor, this room doesn't attack nor receive EMP damage. This room should not be used on ships under level 10 due to the low need of power at those levels. Higher ships should use this when they go full Ion Cannon and EMP Cannon strategy as the power these two rooms take is massive.
The Coal Reactor is still classified as a Reactor in AI Settings. The small size and low power generation makes this room an incredibly easy target for the enemy. Make sure you have a bunch of Armor around this room along with crew. People at levels 10 and 11 won't graze over the damage opportunity like lower level players.
Coal Reactors provide power while it is still upgrading.
Coal Reactors have no functional AI Response.
This room has the most drastically different change for an upgrade out of all rooms in the game.
If you have no Reactors at maximum health, you will always have a 0% Escape Rate, even if you have a Bridge.