Larson Premium Series Exterior Storm Window

Larson’s Premium Series storm windows block 60% of UV radiation with Low-E glass options while delivering air infiltration rates of just 0.14 cfm/ft — four times better than the Performance Series. These discontinued-but-supported windows earned their premium designation through measurable performance advantages that matter in Montana’s climate extremes.

The Premium Series lineup covered every common window configuration before discontinuation in December 2022. The L203/L203E handled double-hung applications from 14.5” to 54” wide and 25.5” to 90” tall. Fixed picture windows got the L503/L503E treatment in sizes from 10” to 80” square. Horizontal sliders used the L603/L603E (25.5”-90” wide, 14.5”-63” tall), while massive three-lite combinations relied on the L623/L623E spanning 42” to 120” wide.

Wind Resistance and Frame Construction

Wind resistance testing proved these windows could handle gusts up to 90 mph — critical for Montana locations exposed to chinook winds or mountain downdrafts. The heavy-duty double-wall tubular T-6 aluminum frame provided the backbone, while double weatherstripping on both sashes and interlocking rails created multiple barriers against infiltration.

That 0.14 cfm/ft air infiltration rate deserves emphasis. Standard storm windows often hit 0.56 cfm/ft or higher. The Premium Series achieved four times better performance than Larson’s own Performance Series. For a typical double-hung window, that difference translates to blocking an additional 15-20 cubic feet per minute of cold air infiltration — enough to feel the difference in both comfort and heating bills.

Wrap-around marine glazing provided thermal barriers and moisture protection at the glass-to-frame junction. Butt-jointed corners and interlocking sashes maintained structural stability under wind loads. Every design decision prioritized defeating air infiltration while maintaining operability through Montana winters.

Energy Performance Specifications

Specification	Value
Air Infiltration	0.14 cfm/ft
UV Blocking (Low-E)	60%
Energy Savings Potential	60% with Low-E glass
ENERGY STAR Certification	Northern/North-Central zones (E models)
Glass Options	Clear single-strength or Low-E double-strength

The Department of Energy recognizes Low-E storm windows as comparable to full window replacement at a fraction of the cost. That 60% energy savings potential comes from combining the air sealing performance with Low-E glass that reflects heat back to its source — keeping warmth inside during winter and outside during summer.

ENERGY STAR certification for Northern and North-Central climate zones confirmed these windows met strict efficiency criteria for Montana’s heating-dominated climate. The Low-E coating specifically targets long-wave infrared radiation while maintaining visible light transmission — critical for passive solar gain through south-facing windows.

Installation Requirements and Tolerances

Installation demands at least 1.5 inches of interior jamb depth, though most Montana homes easily meet this requirement. The frames accommodate out-of-square openings up to 3/8 inch — valuable flexibility in older homes where settling has shifted window frames.

Measurement follows standard protocol: width at top, middle, and bottom using the smallest dimension; height at left, middle, and right using the smallest; then round down to the nearest 1/8 inch. This conservative approach ensures proper fit even with frame irregularities.

Four mounting configurations covered every installation scenario: blindstop (inside mount), overlap (outside mount), exact with expander, and flush-mount with optional expander kits. The flush-mount expander brought the storm window’s outside surface flush with the prime window casing — crucial for maintaining historic home aesthetics.

Tamper-proof one-way installation screws (four included) prevented unauthorized removal — a security feature that also ensured the windows stayed put during wind events. Pre-punched installation holes eliminated drilling through the aluminum frame.

Practical Considerations

Discontinued status as of December 22, 2022, means no new units ship from Larson. However, replacement parts, warranty coverage, and technical support remain available. For contractors sitting on inventory or homeowners with installed units, this continued support matters.

Compatibility extended to single-hung, double-hung, slider, and picture windows. Color options included White, Almond, Brown, and Sandstone — enough variety to match most existing window trim without custom painting.

Sashes removed from inside for cleaning, eliminating ladder work for second-story windows. Heavy-duty metal finger pulls and tilt keys provided leverage for operation even when ice buildup created resistance. Bottom expanders on non-slider models compensated for uneven sills — common in older Montana homes where freeze-thaw cycles have shifted foundations.

The Premium Series earned its designation through quantifiable performance advantages. That 0.14 cfm/ft air infiltration rate and 90 mph wind resistance represent real-world benefits for Montana’s climate. While new units aren’t available, existing installations continue delivering energy savings and draft reduction backed by ongoing manufacturer support.

Frequently Asked Questions

What’s the actual energy savings from Low-E storm windows in Montana?

Larson claimed up to 60% energy savings potential with their Low-E glass option. Real-world savings depend on existing window condition, but the 60% UV blocking and improved air infiltration rates of 0.14 cfm/ft deliver measurable heating bill reductions. The Department of Energy recognizes Low-E storm windows as comparable to full window replacement for energy savings.

Can these storm windows handle Montana’s wind conditions?

Testing proved resistance up to 90 mph winds. The heavy-duty double-wall tubular T-6 aluminum frame combined with double weatherstripping on sashes and interlocking rails creates a system built for extreme conditions. Most Montana locations see gusts well below this threshold, even during chinook events.

How much out-of-square tolerance do these windows allow?

The Premium Series accommodates openings that are out-of-square by up to 3/8 inch. This tolerance handles typical settling in older homes. Proper measurement technique — taking three measurements each for width and height, using the smallest — ensures successful installation even with frame irregularities.

What’s different between model numbers like L203 and L203E?

The “E” designation indicates Low-E glass models. L203 uses standard clear single-strength glass while L203E features high-performance Low-E double-strength glass that blocks 60% of UV radiation and enables up to 60% energy savings. Only the E models earned ENERGY STAR certification for Northern and North-Central climate zones.

Are replacement parts still available after discontinuation?

Yes. Despite discontinuation on December 22, 2022, Larson maintains replacement parts, warranty coverage, and technical support for existing installations. This ongoing support protects the investment for homeowners and contractors who installed these windows before discontinuation.