Gas furnaces form the indoor half of a split system, providing heat and housing the blower that moves air across the cooling coil. Efficiency class determines what venting the installation needs.
Ruud R801T0503A14UHSN 50,000 BTU 80% AFUE Gas Furnace
Ruud R801T0754A17UHSN 75,000 BTU 80% AFUE Gas Furnace
Ruud R801T0754A21UHSN 75,000 BTU 80% AFUE Gas Furnace
Ruud R801T1005A21UHSN 100,000 BTU 80% AFUE Gas Furnace
Ruud R801T1255A24UHSN 125,000 BTU 80% AFUE Gas Furnace
Ruud R801V0503A14UHSC 50,000 BTU 80% AFUE Gas Furnace
Ruud R801V0754A17UHSC 75,000 BTU 80% AFUE Gas Furnace
Ruud R801V1005A21UHSC 100,000 BTU 80% AFUE Gas Furnace
Ruud R801V1255A24UHSC 125,000 BTU 80% AFUE Gas Furnace
Ruud R802V0503A14UHSC 50,000 BTU 80% AFUE Gas Furnace
Ruud R802V0754A17UHSC 75,000 BTU 80% AFUE Gas Furnace
Ruud R802V0755A21UHSC 75,000 BTU 80% AFUE Gas Furnace
Ruud R802V1005A21UHSC 100,000 BTU 80% AFUE Gas Furnace
Ruud R802V1255A24UHSC 125,000 BTU 80% AFUE Gas Furnace
Ruud R951T0403A17M4SN 40,000 BTU 95% AFUE Gas Furnace
Ruud R951T0603A17M4SN 60,000 BTU 95% AFUE Gas Furnace
Ruud R951T0703A17M4SN 70,000 BTU 95% AFUE Gas Furnace
Ruud R951T0855A21M4SN 85,000 BTU 95% AFUE Gas Furnace
Ruud R951T1005A21M4SN 100,000 BTU 95% AFUE Gas Furnace
Ruud R951T1155A24M4SN 115,000 BTU 95% AFUE Gas Furnace
Ruud R951V0603A17M4SC 60,000 BTU 95% AFUE Gas Furnace
Ruud R951V0703A17M4SC 70,000 BTU 95% AFUE Gas Furnace
Ruud R951V1005A21M4SC 100,000 BTU 95% AFUE Gas Furnace
Ruud R951V1155A24M4SC 115,000 BTU 95% AFUE Gas Furnace
The venting decision comes first
An 80% AFUE furnace vents through a conventional metal flue. A 95% or 96% AFUE condensing furnace extracts so much heat from the exhaust that it produces liquid condensate, which requires PVC venting and a drain. Moving between efficiency classes almost always means new venting — sometimes a new flue path through the building. Confirm what your installation can accommodate before choosing.
Sizing
Heating input should follow a Manual J load calculation, not the size of the unit being replaced. Oversized furnaces short-cycle: they heat quickly, shut off, and repeat. That wastes fuel, wears components, and produces uneven temperatures. A correctly sized furnace runs longer at lower output and holds temperature more evenly. The furnace must also be paired with a matched evaporator coil for the combination to carry an AHRI certificate.
Cabinet width
Furnaces are sold in fixed cabinet widths from 14 to 24.5 inches. A replacement that will not fit the existing closet is a common and avoidable problem — the cabinet dimension is listed on every product page. Pre-matched options appear under AC and gas furnace systems.

