Final answer:
Boilers used in greenhouses have nicknames such as "boiler plant", "heat engine", and "hot water generator".
Step-by-step explanation:
One nickname for boilers used in greenhouses is a "boiler plant". A boiler plant refers to a centralized heating system in a greenhouse, where multiple boilers are connected to provide heat to the entire greenhouse.
Another nickname is a "heat engine". Just like an engine converts fuel into mechanical energy, a heat engine converts fuel into heat energy to warm up the greenhouse.
Lastly, boilers used in greenhouses are sometimes called "hot water generators". This term refers to their function of generating hot water, which is then circulated throughout the greenhouse to maintain the proper temperature.