Larson Premium Series Storm Windows: The Air Infiltration Game-Changer

Larson’s Premium Series storm windows achieve 0.14 cfm/ft air infiltration — that’s 4x more effective than their Performance series. In Montana’s climate swings, where you’re fighting 90-degree temperature differentials between inside and outside, that infiltration number matters more than any aesthetic feature.

The Premium Series includes four models covering every window type you’ll encounter. They’re discontinued as of December 2022, but replacement parts, warranty, and support remain available. If you’ve already got them installed or find old stock, they’re still worth maintaining.

Model Configurations and Performance Specs

Each model targets specific window types with size ranges that handle most residential applications:

Model	Type	Width Range	Height Range	Application
L203/L203E	2-Track Double-Hung	14.5” - 54”	25.5” - 90”	Single-hung, Double-hung, Basement windows
L503/L503E	Picture Window (Fixed)	10” - 80”	10” - 80”	Picture windows, Transoms, Fixed openings
L603/L603E	2-Track Slider	25.5” - 90”	14.5” - 63”	Horizontal sliders, Basement windows
L623/L623E	3-Lite Picture/Slider	42” - 120”	14.5” - 63”	Large sliders, Wide openings

The “E” suffix indicates Low-E glass models — the ones that actually move the energy efficiency needle. Standard models come with single-strength clear glass, while Low-E models upgrade to double-strength glass that blocks 60% UV and claims 60% energy savings. That UV blocking matters when you’re protecting wood floors and furniture from Montana’s high-altitude sun.

All models share the same heavy-duty double-wall tubular T-6 aluminum frame construction. Tested up to 90 mph wind resistance — sufficient for chinook gusts coming off the Front. The double weatherstripping on sashes and interlocking rails creates that exceptional air infiltration performance.

Energy Performance That Actually Matters

Low-E models (L203E, L503E, L603E, L623E) carry ENERGY STAR certification for Northern/North-Central zones — exactly where Montana sits. The Department of Energy recognizes Low-E storm windows as comparable to full window replacement at a fraction of the cost.

Here’s what makes the difference: wrap-around marine glazing creates a thermal barrier and moisture protection. Combined with interlocking sashes for stability, the system maintains its seal even as frames flex with temperature changes.

The 0.14 cfm/ft infiltration rate beats most primary windows, let alone storm windows. For comparison, new double-hung windows typically test at 0.30 cfm/ft or higher. You’re essentially cutting air leakage by more than half by adding these storms.

Installation Tolerance for Real-World Applications

These windows handle out-of-square openings up to 3/8 inch — crucial for older Montana homes where settling and wood movement have tweaked the geometry. Minimum interior jamb depth requirement is 1.5 inches.

Four mount types give you options: Blindstop (inside mount), Overlap (outside mount), Exact with Expander, and Flush-Mount with optional expander. The variety matters when you’re dealing with different window trim profiles and siding conditions.

Measurement procedure is standard but critical: measure width at top, middle, and bottom using the smallest measurement; height at left, middle, and right using the smallest; then round down to the nearest 1/8 inch. Get it wrong and you’re making another trip to the job site.

Frequently Asked Questions

Q: Are Premium Series storm windows still available new? A: No, they were discontinued December 22, 2022. However, replacement parts, warranty support, and service remain available through Larson.

Q: What’s the actual difference between Premium and Performance series? A: Air infiltration is 4x better on Premium (0.14 cfm/ft vs higher values), Premium uses double weatherstripping versus Performance’s wool-pile, and Premium features a heavier tubular aluminum frame. Premium also carried a Limited Lifetime warranty versus Performance’s 10-year.

Q: Do Low-E storm windows really save as much as window replacement? A: The DOE recognizes Low-E storm windows as comparable to full window replacement for energy savings. The Low-E glass blocks 60% UV and claims 60% energy savings, though actual savings depend on your existing windows’ condition.

Q: Can these handle Montana’s wind conditions? A: They’re tested to 90 mph, which covers most Montana wind events including typical chinook gusts. For extreme exposures near the Rocky Mountain Front, consider additional fastening.

Q: What tools come with the windows? A: Four tamper-proof one-way installation screws are included. Units feature pre-punched installation holes, and non-slider models include a bottom expander for uneven sills.