forewarmer
/ˈfɔːrˌwɔːrmər/Definitions
1. noun
A device or appliance for warming the air before it reaches a heater or a warmer.
“The house had a forewarmer connected to the central heating system.”
2. noun
A person who warms or prepares the way for something.
“The forewarmer of the new restaurant helped to create a buzz in the local community.”