3.5-5 Ton Gas Furnace, Single Stage, Upflow/Horizontal, 88,000 BTU

Armstrong Air 85W31 – A80 Series 80 % AFUE Gas Furnace, 88 000 BTU Input

The Armstrong Air 85W31 furnace is an 80 % AFUE, single-stage heating appliance rated at 88 000 BTU input (≈70 000 BTU output). Sized for 3.5 – 5 ton airflow applications, the unit is suitable for upflow or horizontal installations in residential mechanical rooms, closets, or attics where space is at a premium. A 33-inch cabinet height and left/right utility knock-outs simplify retrofits and new construction layouts.

Construction and Component Overview

• Heat Exchanger – Non-welded aluminized-steel clamshell design resists thermal fatigue and minimizes leakage risk.
• Ignition System – Silicon-nitride hot-surface igniter replaces standing pilot assemblies for reliable, low-amp start-up.
• Blower Assembly – Constant-torque ECM motor (multi-tap) delivers stable airflow across a broad static range; slide-out rack speeds service tasks.
• Gas Control – Single-stage valve provides full-fire operation for straightforward setup and diagnostics.
• Service Access – Hinged door with quarter-turn fasteners; integrated sight port for burner inspection; field-selectable left/right gas and electrical connections.

Key Performance Data

• Model Number: 85W31 | Nominal tag A80UH1E090/110 series*
• Input Capacity: 88 000 BTU h
• AFUE: 80 %
• Blower Motor: Constant-torque ECM, multi-speed
• Airflow Range: 1 400 – 2 000 CFM (3.5-5 ton)
• Orientation: Upflow / Horizontal
• Cabinet Dimensions: 33 in H × 21 in W × 28 in D (C-width)

*Confirm exact suffix and rating plate before ordering replacement parts.

Installation & Commissioning Notes

Set-up must be completed by a licensed HVAC professional. Verify duct static pressure, temperature rise, gas supply pressure, and combustion readings per Armstrong Air start-up checklist. When matched with a properly sized evaporator coil and 13-SEER or higher outdoor unit, the furnace supports cooling airflow requirements up to 2 000 CFM.