Gravity-style furnace subunit inside a gas-induced draft furnace

A gravity-style furnace subunit for a gas-induced draft furnace. A heat conduction tube configured to be located inside of a gas-induced draft furnace cabinet, the heat conduction tube being separated from a row of draft-induced heat conduction tubes inside the cabinet. A burner assembly having a burner tube located within the heat conduction tube through an inlet opening of the heat conduction tube. The burner assembly permits air flow through the inlet opening into the heat conduction tube. A pilot assembly located within the heat conduction tube and adjacent to the burner tube. A thermopile module having located adjacent to a flame outlet of the pilot assembly within the heat conduction tube. A gas valve configured to control gas flow to the burner assembly, the gas valve electrically coupled to the thermopile module and to actuate gas flow there-through when the thermopile module generates a predefined voltage difference.