Still heating with a furnace from the 1970s, '80s or '90s? Every new furnace on this page is rated 96% AFUE or better. That means at least 96 cents of every gas dollar becomes heat in your home. Older furnaces waste 20 to 45 cents of it up the chimney. Below you'll find Good, Better and Best options from the brands our supply houses stock, plus an old-vs-new comparison and an estimate of what you could save on gas each year.
Old standing-pilot, natural-draft furnace (roughly 1960s–1980s)
Efficiency
about 55–65% AFUE (estimate for this type of furnace)
Ignition
a standing pilot flame that burns 24/7, all year, even in summer
Venting
natural draft through a draft hood into a metal flue or chimney; hot flue gas rises on its own
Safety
if the chimney is blocked, cold or the house is depressurized, combustion gas can spill back into the house (backdraft). That can bring carbon monoxide (CO) into living space. Cracked heat exchangers are common at this age.
Blower
single-speed, loud on/off cycling
Parts
many parts are no longer made
Image: Goodman Manufacturing
80% AFUE, induced-draft furnace (standard since the 1990s)
Efficiency
80% AFUE
Ignition
electronic (hot-surface) ignition; no standing pilot
Venting
an inducer fan pushes flue gas into a metal B-vent or chimney liner
Safety
much better than natural draft, but still shares a metal flue (often with the water heater) that must be sized and lined correctly
Blower
usually single-stage heat; older ones have single-speed blowers
Heat lost
about 20% of the heat goes up the flue
Image: Amana Brand
New 96%+ condensing furnace (what we install)
Efficiency
96% to 97.5% AFUE on the models below
Ignition
electronic ignition; no pilot burning gas all year
Venting
sealed combustion. A second heat exchanger pulls extra heat out of the flue gas, so it's cool enough to vent through PVC pipe out a side wall or the roof. Many installs bring combustion air in from outdoors through a second PVC pipe, so the furnace doesn't draw air from inside your house.
Safety
no draft hood, no shared chimney, no backdraft through a draft hood
Comfort
two-stage or modulating models run longer at low fire for steadier temperatures and quieter operation; variable-speed blowers move air gently
Note
condensing furnaces make water, so they need a condensate drain (we plan for this on every install)
Any fuel-burning appliance can produce carbon monoxide. Every home with a gas furnace should have working CO alarms. If your furnace still has a standing pilot and a draft hood, ask us to check the venting and heat exchanger on your next visit.
All models below are rated 96% AFUE or higher by the manufacturer. Exact AFUE varies by size (BTU input) and configuration, and every installed furnace has its own AHRI certificate. Your written quote will show the exact model and its AHRI rating.
Good
Image: Goodman Manufacturing
Goodman GR9S96
GR9S96 (single-stage, multi-speed ECM blower)
AFUE
up to 96%
Gas valve
single-stage
Blower
multi-speed ECM
96%+ AFUE
A dependable, no-frills high-efficiency furnace from one of the most widely stocked brands in Denver. Same 96% efficiency class as the premium models, with simpler controls and fewer parts. Also available in this tier: Amana AR9S96.
Two-stage heat runs on low fire most of the winter, which means fewer on/off cycles, steadier temperatures and quieter operation. Built by Trane. Also available in this tier: Amana ARVT96 two-stage variable-speed (up to 97.5% AFUE).
Shown: Trane XC95m, a Best-tier alternative.Image: Trane
Amana ARVM97 Modulating Furnace
ARVM97 (modulating gas valve, variable-speed blower)
AFUE
97%
Gas valve
self-calibrating modulating
Blower
variable-speed ECM
96%+ AFUE
A modulating furnace adjusts its flame in small steps to match how much heat your home needs right now, instead of just on or off. The result is the most even temperatures, the quietest operation and the best comfort on Denver's swing-season days. Also available in this tier: Goodman GRVM97 and the Trane 96 Modulating Variable Speed furnace (XC95m, up to 97.3% AFUE).
Good / Better / Best reflects comfort features, controls and warranty. All three tiers are in the same high-efficiency class, so yearly gas use is close between them (see the table below). We'll size the furnace to your home with a load check, not by matching the old furnace's size. Product images are the manufacturers' stock photos, used for reference.
How much gas could you save? (Estimates, October 2026)
Example yearly gas costs for the same Denver-area home with different furnaces. These are estimates, not guarantees. Your savings depend on your home, insulation, thermostat settings, weather and gas prices.
Furnace
AFUE
Gas used per year
Estimated gas cost per year
Estimated savings per year with a 96% furnace
Old standing-pilot, natural-draft
about 60% (estimate)
about 1,170 therms
about $1,264
about $474
80% induced-draft
80%
about 878 therms
about $948
about $158
Good / Better: 96% condensing
96%
about 731 therms
about $790
(baseline)
Best: 97% modulating
97%
about 724 therms
about $781
about $9 more than 96%
Going from a standing-pilot furnace to a 96% furnace can cut the gas used for heating by roughly 40%. Going from an 80% furnace to 96% cuts it by about 17%. A standing pilot alone also burns gas every hour of the year, including all summer. The move from 96% to 97% saves only a little gas; the Best tier is mainly about comfort and quiet.
Home heating load: 70.2 million BTU of delivered heat per year for an existing Colorado home, from the Xcel Energy Colorado deemed-savings sheet: Xcel Energy Colorado deemed-savings sheet.
Gas price: about $1.08 per therm, all-in, from Colorado's 2025 average residential natural gas price ($11.17 per thousand cubic feet, at 10.37 therms per thousand cubic feet). U.S. EIA: U.S. EIA.
Gas used = heating load ÷ AFUE. The 60% figure for a standing-pilot furnace is an estimate for illustration. Estimates prepared October 2026. Same assumptions as our heat pump page, so the two pages can be compared.
Repairs are getting frequent, or parts are hard to find
Rooms are uneven, or the furnace is loud when it starts
Your gas bill keeps climbing
A technician has found a cracked heat exchanger or venting problems
Thinking about a heat pump too?
If you also need a new air conditioner, a cold-climate heat pump paired with a new high-efficiency furnace (dual fuel) lets the heat pump handle cooling and much of the heating, with the furnace covering the coldest days. See our cold-climate heat pump options.
Who will install it
EPA Section 608 Universal certified
Xcel Energy Quality Installation Assessment training
Ongoing manufacturer and industry training
Every install is sized with a load check, with a sealed PVC vent and condensate drain planned for your home
Every quote lists the exact model and its AHRI certificate
Gas Furnace FAQ
Ready to retire that old furnace? Tell us about your current system and we'll recommend a Good, Better or Best furnace sized for your home.
