Safe furnace set up consists of testing for gas leaks, confirming suited vent slope

https://www.scribd.com/document/980978088/Canadian-Heating-and-Air-Conditioning-Explains-Furnace-BTU-Requirements-185138

Safe furnace deploy entails trying out for gas leaks, confirming true vent slope, and guaranteeing ok combustion air for trustworthy wintry weather warmness.