how can you tell what level a room is? i put a power plant next to a larger one that was already merged. my understanding is they will only merge if they are the same level, but i can't figure out how to match the levels. thanks!

Tap on the new room you built, then tap the up-arrow in the right top of the screen and upgrade the room. If the room is the same level (and the same type of course) as the adjacent rooms after the upgrade, they will automatically merge.

that doesn't work. i've upgraded two adjacent power plants (one is a single room, one is two rooms merged) and they aren't combining.

The name of the room changes as it levels up.

(only 3 rooms in a row will combine)

/\ boom. that was it. 3 room limit hit. thanks!