How to Choose a Window Contractor in Denver (2025)

Colorado does not require a specific window installation license. Denver requires a city contractor license. Always verify general liability insurance and workers' compensation before work begins.

For energy-efficient window claims, look for contractors who are certified installers for the brands they sell. Andersen, Pella, and Marvin have certified installer programs. Certification means the contractor has been trained on proper installation for that specific product.

Denver's climate requires specific window performance specs:

U-factor: 0.30 or lower for Denver's cold winters. This measures heat loss — lower is better.

SHGC (Solar Heat Gain Coefficient): 0.25–0.35 for most Denver homes. Balances winter solar gain with summer heat rejection.

Low-E coating: Essential for Denver. Reflects UV and infrared radiation, reducing summer heat gain and winter heat loss.

Gas fill: Argon or krypton between panes — verify it's included, not just offered as an upgrade.

Ask any window contractor to provide the NFRC label specs for the windows they're proposing. If they can't, that's a red flag.

The most common window failure is improper installation, not product defects. Proper window installation in Denver requires:

Flashing: Water-resistive barrier and flashing tape around every window opening. Critical in Denver's hail and wind-driven rain environment.

Insulation: Gaps between window frame and rough opening must be filled with low-expansion foam — not fiberglass batts, which allow air infiltration.

Leveling and squaring: Windows must be perfectly plumb, level, and square. Improper alignment causes operational problems and seal failure.

Ask: What is your flashing process? What do you use to insulate around the frame? Specific answers indicate experience.

Get 3 quotes. Each should specify: window manufacturer and product line, frame material, glass package (U-factor, SHGC, Low-E, gas fill), installation process including flashing, removal and disposal of old windows, and warranty on both product and labor.

Be cautious of contractors who only sell one brand — a reputable window contractor can explain why their recommended product is the best fit for your home and budget, not just what they happen to carry.