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Trane
40,000 BTU Gas Furnace
Trane 80% AFUE, Single-Stage, Upflow/Downflow/Horizontal, 14.5" Cabinet | S8X1A040M3PSC
$1,832.99
A 40,000 BTU gas furnace covers small-to-mid-size homes with a light-to-moderate heating load. Beyond size and efficiency, this is a good point to think about how the burner runs — single-stage, two-stage, or modulating — because it shapes how even and quiet the heat feels.
22 products
Trane
Trane 80% AFUE, Single-Stage, Upflow/Downflow/Horizontal, 14.5" Cabinet | S8X1A040M3PSC
Trane
Trane 80% AFUE, Single-Stage, Upflow/Downflow/Horizontal, 17.5" Cabinet | S8X1B040M2PSC
Trane
Trane 80% AFUE, Two-Stage, Upflow/Downflow/Horizontal, 14.5" Cabinet | S8X2A040M3PSC
Trane
Trane 80% AFUE, Two-Stage Variable Speed, Upflow/Downflow/Horizontal, 14.5" Cabinet | S8V2A040M3PCB
Trane
Trane 96% AFUE, Single-Stage, Upflow/Left/Right, 17.5" Cabinet | S9X1B040U3PSB
Trane
Trane 96% AFUE, Two-Stage, Upflow/Left/Right, 17.5" Cabinet | S9X2B040U3PSB
Goodman
Goodman Single-Stage, Downflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet | GD9S800403AN
Goodman
Goodman Single-Stage, Downflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet, Low-NOx | GD9S800403AX
Goodman
Goodman Single-Stage, Upflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet | GR9S800403AN
Goodman
Goodman Single-Stage, Upflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet, Low-NOx | GR9S800403AX
Goodman
Goodman Single-Stage, Upflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet, Ultra-Low NOx (CA) | GR9S800403AU
Goodman
Goodman Two-Stage, Downflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet, Low-NOx | GD9T800403AX
Goodman
Goodman Two-Stage, Upflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet | GR9T800403AN
Goodman
Goodman Two-Stage, Upflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet, Low-NOx | GR9T800403AX
Goodman
Goodman Single-Stage, Upflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet | GR9S920403AN
Goodman
Goodman Single-Stage, Downflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 17.5" Cabinet | GD9S960403BN
Goodman
Goodman Single-Stage, Upflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet | GR9S960403AN
Goodman
Goodman Single-Stage, Upflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 17.5" Cabinet, Ultra-Low NOx (CA) | GR9S960403BU
Goodman
Goodman Two-Stage, Downflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 17.5" Cabinet | GD9T960403BN
Goodman
Goodman Two-Stage, Downflow/Horizontal, Variable-Speed ECM, Communicating, 40,000 BTU, 3 Ton Airflow, 17.5" Cabinet | GDVT960403BN
Goodman
Goodman Two-Stage, Upflow/Horizontal, Multi-Speed ECM, 40,000 BTU, 3 Ton Airflow, 14" Cabinet | GR9T960403AN
Goodman
Goodman Two-Stage, Upflow/Horizontal, Variable-Speed ECM, Communicating, 40,000 BTU, 3 Ton Airflow, 17.5" Cabinet | GRVT960403BN
A single-stage furnace is either full-on or off, which can mean warm blasts followed by cool-downs. A two-stage furnace runs on a gentler low setting most of the time and steps up only when needed, so temperatures stay steadier and it's quieter. Modulating furnaces fine-tune output continuously for the most even heat. Higher staging costs more but noticeably improves comfort.
Wondering whether two-stage is worth it in a 40,000 BTU furnace? Ask us →
A single-stage furnace runs at full output whenever it's on. A two-stage furnace has a low and a high setting, running mostly on low for steadier, quieter heat and stepping up only on the coldest days.
If even temperatures and quiet operation matter to you, often yes — especially paired with a variable-speed blower. In a small home with modest needs, a single-stage unit still heats reliably for less.
A modulating furnace continuously adjusts its flame and output rather than switching between fixed stages, holding the most consistent temperature of any type. It's the premium option for comfort and efficiency.
Small-to-mid-size homes with a light-to-moderate heating load, confirmed by a load calculation for your climate and insulation.