Curated comparison
Carrier Infinity 97 vs Infinity 98: the 80,000 BTU/h communicating furnaces
A same-size comparison of Carrier's communicating two-stage Infinity 97 and modulating Infinity 98, using Carrier's published product data for both.
Short answer
The Infinity 97 (59TN7A 080C21–20) is a communicating two-stage furnace: low and high fire at 52,000 and 80,000 BTU/h input. The Infinity 98 (59MN7C 080C21–20) is the modulating version: its input steps continuously from 32,000 to 80,000 BTU/h, with a variable-speed inducer and a certified 97.2% AFUE. The 98 is Carrier's most precise and most expensive residential furnace; the 97 delivers two-stage comfort on the same communicating platform for less.
| Specification | 59TN7A 080C21–20 | 59MN7C 080C21–20 |
|---|---|---|
| AFUE, upflow | 97 % | 97.2 % |
| AFUE, horizontal | 96.7 % | — |
| AFUE, downflow | 95 % | 95 % |
| Cabinet width | 21 in | 21 in |
| Approximate shipping weight | 171.5 lb | 161 lb |
| Cooling airflow @ 0.5 in. w.c. | 1,985 CFM | 2,035 CFM |
| Cooling capacity match | 4.5 tons @ 400 CFM/ton; 5.5 tons @ 350 CFM/ton | 4.5 tons @ 400 CFM/ton; 5.5 tons @ 350 CFM/ton |
| Blower motor | 1 HP | 1 HP |
| Maximum unit amps | 13.1 A | 14.4 A |
| Maximum fuse / breaker | 20 A | 20 A |
Staging is the whole story. The Infinity 97 has two gas rates: 52,000 BTU/h input on low fire and 80,000 BTU/h on high, with outputs of 50,000 and 76,000 BTU/h. The Infinity 98 modulates: Carrier publishes 32,000 BTU/h minimum, 52,000 BTU/h intermediate and 80,000 BTU/h maximum inputs, with outputs of 31,000, 51,000 and 78,000 BTU/h, plus a variable-speed inducer matched to the burner.
Efficiency is close: Carrier certifies the Infinity 97 at 97.0% AFUE upflow and 96.7% horizontal, and the Infinity 98 at 97.2% upflow and horizontal, both 95.0% downflow. The efficiency gap is not the reason to buy the 98; the reason is low-capacity operation: on mild days the 98 can hold the house at minimum fire instead of cycling between off and full.
Both are communicating furnaces for the Infinity system with constant-airflow ECM blowers, in the same 21-inch cabinets with similar electrical requirements (20 A maximum breaker on each). The 98 adds the modulating gas valve, variable-speed inducer and the 98.5%-certified 060C21–20 sibling at the small end of the family.
Which one wins depends on the house: steady small heat loss favors the 98's long low-fire runs; a house that rarely needs less than low-fire output pays for modulation it cannot use. Sizing follows a heat-loss calculation for both, and the 98's set-up and control configuration matter more than on any other family here.
Questions people ask
Is the Infinity 98 much more efficient than the Infinity 97?
No: 97.2% versus 97.0% upflow in Carrier's data for these sizes. The 98's value is its modulating range and steadier low-capacity operation, not its AFUE.
Can the Infinity 97 do what the Infinity 98 does?
No. The 97 steps between two gas rates; the 98 varies continuously across its range. If most of the heating season is mild, the modulating furnace runs at low capacity for long periods, which is the comfort difference.
Talk it through before you decide
A consultation covers sizing, staging, venting and whether a heat pump belongs in the plan. No purchase required.