40,000 BTU Upflow Furnaces

Forty thousand BTU is the smallest capacity in the residential furnace range, and it is the right size more often than people expect. A tight condo, a well-insulated ranch, a cabin or an addition on its own duct run all lose less heat than a 60,000 or 80,000 BTU furnace was built to replace, and an oversized unit short-cycles, wears its igniter and leaves rooms alternating between too warm and too cool. Sizing to the actual heat loss is what keeps the house even.

Every natural gas furnace here is upflow, meaning air enters from the bottom and leaves through the top, which is the standard orientation for a basement or closet install with ducts overhead, and each one can also be turned on its side for a horizontal attic or crawlspace run. If your ducts drop from a furnace above the living space instead, our 100,000 BTU downflow furnaces show the other orientation, and our upflow versus downflow furnace guide walks through which one your ductwork calls for.

Why Choose 40,000 BTU Furnaces from HVAC Store?

• We stock 80, 92 and 96 percent AFUE models in single stage and two stage, so you choose efficiency against budget rather than settling.

• Orders over $1,000 ship free to the 48 contiguous states, and most states outside California pay no sales tax.

• Find the same furnace priced lower elsewhere and we will match it under our lowest price guarantee.

• Our specialists confirm cabinet width, blower airflow and venting requirements before your order ships.

You Might Also Like

• Upflow Furnaces - Every upflow capacity we carry, from 40,000 BTU up, if the heat loss calculation lands above this page.

• 60,000 BTU Upflow Furnaces - The next size up, for mid-size homes and colder climates where 40,000 BTU falls short.

• Goodman Upflow Furnaces - The complete Goodman upflow line across all capacities and efficiency tiers.

Best 40,000 BTU Furnaces for...

Everyday High-Efficiency Heating in a Compact Cabinet

The best 40,000 BTU furnace for most homes is a 96 percent AFUE single-stage unit in a narrow cabinet. The Goodman 96% 40,000 BTU Gas Furnace Single Stage 14" Width Upflow/Horizontal fits a 14 inch closet and vents in PVC.

Milder Climates and Short Heating Seasons

The best 40k BTU furnace for a mild climate is an 80 percent AFUE model, because the efficiency premium never pays back when the furnace runs a few weeks a year. The Goodman 80% 40K BTU Gas Furnace 9-Speed 14"W Single Stage Upflow/Horizontal uses standard metal venting.

Quiet, Even Heat in Open Living Spaces

The best gas furnace at 40,000 BTU for comfort is a two stage unit that runs on low most of the time. The Goodman 96% 40K BTU Gas Furnace Two Stage 17.5"W Cabinet Upflow/Horizontal holds temperature without the on-off swings of a single stage burner.

Low-NOx Emission Jurisdictions

The best 40,000 BTU gas furnace for California air districts with ultra-low NOx rules is one certified to those limits. The Goodman 96% AFUE 40K BTU Gas Furnace 9-Speed Ultra-Low NOx 17.5"W Upflow/Horizontal meets them at 96 percent efficiency.

Quick Spec Comparison

Every furnace in this collection is a Goodman 40,000 BTU input unit on 115 volt power that installs upflow or horizontal. Efficiency, staging, cabinet width and emissions rating are what change between them.