When the combustion air duct is connected directly to the return plenum for a furnace, the blower fan on the furnace pulls outdoor air in to the return plenum. To supply this air to the furnace room, ...
The Family Handyman on MSN
How Does a Gas Furnace Work?
If you need to purchase a gas-burning forced-air furnace but aren't sure how they work, here's what you need to know.
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