Done! installs a wide range of residential gas furnaces, including single-stage, two-stage, and variable-speed (modulating) models from leading manufacturers. We match the right furnace to your home’s size, existing ductwork, and efficiency goals — and we account for Colorado’s altitude when selecting and configuring equipment, since high-elevation combustion affects how furnaces are sized and tuned.

Single-Stage, Two-Stage, and Variable-Speed Furnaces

The main types of gas furnaces vary in how they control heat output:

  • Single-stage: Operates at full capacity whenever it runs — simple, reliable, and the most affordable upfront. Best for smaller homes or budget-focused replacements.
  • Two-stage: Runs at a lower capacity (typically around 65%) most of the time and ramps up to full capacity only on the coldest days. More consistent temperatures, quieter operation, and better efficiency than single-stage.
  • Variable-speed (modulating): Continuously adjusts output to match your home’s exact heating demand. The most efficient option, with the most even comfort and best humidity control — a meaningful benefit in Colorado’s dry winters.

High-Efficiency vs. Standard-Efficiency Models

Modern furnaces are rated by Annual Fuel Utilization Efficiency (AFUE). A 96% AFUE furnace converts 96 cents of every dollar of gas into heat; an 80% AFUE unit loses 20 cents up the flue. At Denver’s natural gas rates, the efficiency gap between an older furnace and a modern high-efficiency unit can add up to meaningful annual savings. High-efficiency furnaces use a secondary heat exchanger and typically vent through PVC pipe rather than a metal flue — a factor our installers account for during the job scope.

Altitude Matters in Colorado

At 5,280 feet, there’s less oxygen available for combustion than at sea level. Furnaces installed in the Denver metro are typically derated — adjusted to run at a lower BTU output — to account for this. An improperly sized or configured furnace can short-cycle, overwork its heat exchanger, or fail to heat your home adequately. Done!’s installation team understands Colorado’s elevation requirements and follows manufacturer specs and local code for proper deration and venting.

What About Heat Pumps?

If you’re open to alternatives to a gas furnace, modern cold-climate heat pumps have improved dramatically and can operate efficiently even on Front Range winter nights. Some homeowners opt for a dual-fuel system — a heat pump for most of the heating season with a gas furnace as a backup for extreme cold. Done! installs heat pump systems and can walk you through whether a hybrid setup makes sense for your home and utility situation.

The Installation Process

A proper furnace installation starts with a load calculation — not a guess based on your old unit’s size. We assess your home’s square footage, insulation, window area, duct condition, and local climate to right-size the new system. An oversized furnace short-cycles and wears out faster; an undersized one runs constantly and can’t keep up on the coldest nights. After installation, we test the system thoroughly, including checking gas pressure, heat rise, and airflow before we leave.

Ready to replace an aging furnace or want to explore your options? Visit our furnace installation page or schedule a no-obligation assessment with Done! — we’ll help you find the right system for your home and budget, with financing available for qualified customers.