Cold Climate Windows
Window selection guide for IECC Climate Zone 5: Cold climates including Boise, Denver, Chicago, and northern tier cities.
Energy Code Requirement
U-0.32
U-Factor Maximum
Solar Heat Gain
No requirement (but 0.35-0.45 recommended for passive solar)
SHGC Requirement
Heating Degree Days
5,000-7,000 annually
Annual Average
Climate Zone Zone 5 Characteristics
Temperature & Climate
- Climate Type
- Cold (Cold-Dry and Cold-Humid)
- Average Summer
- 80-90°F (27-32°C)
- Average Winter
- 15-35°F (-9 to 2°C)
- Cooling Degree Days
- 600-1,500 annually
Energy Priorities
- Primary Concern
- Heating costs dominate (70-75% of energy bill)
- Secondary Concern
- Moderate cooling needs in summer
Specific Challenges for Cold Climates
- ▸Cold winters require excellent insulation (U-factor critical)
- ▸Heating costs 3-4x cooling costs (focus on heat retention)
- ▸Temperature extremes (-10°F to 100°F) stress seals
- ▸Condensation and frost on windows in winter
- ▸Ice damming can affect window frames
- ▸Triple-pane increasingly standard for energy savings
Energy Code Requirements
- Energy Code
- IECC 2018/2021 Climate Zone 5
- Air Leakage Maximum
- ≤0.3 cfm/ft²
- Additional Notes
- U-factor is critical. Triple-pane recommended for 20-30% additional savings. Low-E2 coating captures passive solar heat in winter.
Recommended Window Configurations
Standard Cold Climate
Budget- Pane Count
- Double-pane
- Low-E Coating
- Low-E2 (passive, keeps heat in)
- Gas Fill
- Argon fill
- Frame Material
- Vinyl
- U-Factor
- U-0.28 to U-0.32
- SHGC
- SHGC 0.35 to 0.45
- Cost Range
- $500-$800 per window
- Payback Period
- 6-8 years
High-Performance Triple-Pane
Premium- Pane Count
- Triple-pane
- Low-E Coating
- Low-E2 or Low-E4
- Gas Fill
- Krypton fill
- Frame Material
- Fiberglass or vinyl
- U-Factor
- U-0.15 to U-0.22
- SHGC
- SHGC 0.30 to 0.40
- Cost Range
- $750-$1,200 per window
- Payback Period
- 8-12 years, excellent heating cost reduction
Common Window Problems in Cold Climates
- Severe condensation and frost in winter
- High heating costs driving need for U-0.22 or better
- Ice damming affecting window frames and seals
- Thermal stress cracks from rapid temperature changes
- Energy loss through older single/double-pane windows catastrophic
- Frame expansion/contraction from temperature cycling
Energy Cost Analysis
Annual Heating
$1,400-$2,200
Annual Cooling
$400-$700
Potential Savings
$400-$650/year with triple-pane U-0.20
Utility Rate
$0.09-$0.12/kWh
Recommended Window Products
Andersen
A-Series Triple-Pane with Low-E4
U-0.19, SHGC 0.36, Argon/krypton fill
Pella
450 Series Triple-Pane
U-0.20, SHGC 0.35, Energy Star Most Efficient
Marvin
Ultimate Triple-Pane
U-0.17, SHGC 0.32, Cold climate certified
Note: Product availability and specifications may vary. Always verify current specs with manufacturers and local dealers.
Cities in Climate Zone Zone 5
Boise, ID
5800 HDD • U-0.32 or lower for residential windows
Denver, CO
6000 HDD • U-0.32 or lower for residential windows
Spokane, WA
6800 HDD • U-0.30 or lower for residential windows
Salt Lake City, UT
6000 HDD • U-0.32 or lower for residential windows
Chicago, IL
6500 HDD • U-0.32 or lower for residential windows
Boston, MA
5600 HDD • U-0.30 or lower for residential windows (strict)