798 vs. 900 Series Aluminum Windows: What’s the Difference?
Chad Crenshaw
Both the 798 and 900 series are extruded aluminum window systems, and the real difference comes down to the frame profile, the glass depth each one carries, and how much thermal performance you build into the opening. The 900 series is engineered for homes that want a deeper, more efficient frame; the 798 series is a solid choice when you need a slimmer, lighter profile. Both are thermally broken and both accept the same premium 1" double-pane argon-filled Low-E tempered glass, so the pick is about how much frame and glazing your openings need.
What Do the Series Numbers Mean?
Series names describe a family of frame profile built for a specific performance and appearance level. They aren’t a brand or a model number — they tell you how deep the extrusion is and what it can carry.
- A series defines frame depth, wall thickness, and how the thermal break is engineered.
- Choosing a series is how you set the balance of strength, slim sightlines, and insulation.
- The right series depends on your opening size, glass load, and efficiency goals.
- Every aluminum window on your project should be spec’d by series, not picked by photo.
It helps to think of the series as the skeleton of the window. It decides how much glass the sash can hold, how stiff the operating vent feels, and how much thermal separation the frame can keep. Get the series wrong and the rest of the window is working against itself from day one.
Both 798 and 900 come out of the same extruded aluminum family, so the metal quality and factory process are identical. The differentiation happens at the die — deeper frames use more aluminum, which changes the weight, the sightline, and the price. That’s why the two series coexist: they solve different openings, not different quality tiers.
A slimmer frame keeps the view open and the window light, which is why 798 is popular for standard window walls and non-glare living spaces. But a slimmer profile also means less room for glass and a smaller air pocket inside the frame. When you push for maximum energy performance or a very large pane, the deeper section has more to work with. It is not that one is “better built” — it is that each is shaped for a different job, and the engineering has to match the opening.
How Do the 798 and 900 Series Compare?
Side by side, the series differ most in frame size and the depth of glass they carry. That one difference drives most of the performance gap between them.
- Frame profile: The 798 is a slimmer extrusion; the 900 is a deeper, more substantial profile.
- Glass depth: The 900 series is built around a thicker, higher-performance glass package.
- Thermal break: Both use a bend engineered into the extrusion geometry with air gaps that slow heat transfer, tuned to each profile’s depth.
- Best fit: 798 fits lighter, more economical bays; 900 suits openings where max efficiency and strength matter.
- Hardware: Both systems run German-engineered hardware built for daily operation and a clean seal.
Because both series share the engineered thermal break, neither is a “cold” window. The difference is how much performance headroom the frame gives you. On a large picture window or a bank of fixed glazing, the 900’s deeper extrusion holds more glass with less flex.
Thermally broken aluminum matters most in Texas, where summer heat tries to push straight through the frame. A deeper series keeps more of that heat on the outside.
The table below is a quick way to match the two series to a typical project.
- Standard window wall — 798 series keeps sightlines slim and cost controlled.
- Large fixed picture window — 900 series carries the heavier glass without flex.
- High-glare south or west exposure — 900 series plus Low-E gives the most headroom.
- Whole-home window replacement — a mix of both, sized per opening.
You do not have to pick one series for the whole house. The right move is often per-opening: 798 where you want light and economy, 900 where the glass is big or the sun is harsh. A qualified consultant sizes each opening so you don’t overpay for depth you don’t need, or underspec the pane that takes the heat.
Which Series Should I Choose?
Choose by what the window needs to carry and how much performance you want in the frame. Start with the opening, then work up to the series.
- Pick the 798 series for a slim, economical profile on standard openings.
- Pick the 900 series for deeper frames, a bigger glass package, and maximum efficiency.
- Either way you get 1" double-pane argon-filled Low-E tempered glass and a thermally broken frame.
- Your consultant can size the right series to your openings on a window walkthrough at one of our 4 DFW showrooms.
A common mistake is ordering the slim 798 on a large high-glare opening and then being surprised the sash flexes or the room runs warm. Map every opening’s size and sun exposure first; the series should follow the glass, not the photo.
If efficiency is the goal and you’re weighing materials, compare a thermally broken aluminum system against other frame types before you commit.
Why Series Choice Matters for Performance
The frame is part of the full window system, so the series sets the floor for efficiency, durability, and how the whole opening performs. Get the floor wrong and nothing above it can be saved.
- Frame depth affects how much glass the window carries and how the sash seals when closed.
- A deeper extrusion supports heavier glazing and stiffer, more reliable operation over years of use.
- Both series share the engineered thermal break, so efficiency comes from the complete package, not one part.
Series choice also drives the visual result. A slimmer 798 keeps sightlines light and modern; a deeper 900 reads more substantial and frames the view. Your design intent matters as much as the numbers on the spec sheet.
Once the right series is set, confirm the glass, finish, and hardware before production so the window ships exactly as designed. Your consultant can walk the opening, the glass package, and the series together — schedule your free consultation to lock in the fit.
FAQ
Q: What is the difference between 798 and 900 series aluminum windows?
A: The 798 is a slimmer profile suited to standard lighter openings, while the 900 is a deeper extrusion that carries a larger high-performance glass package for maximum efficiency.
Q: Are both series thermally broken?
A: Yes. Both use a thermal break engineered as a bend in the extrusion geometry that creates air gaps, scaled to each frame profile — not a separate insert.
Q: Which series is more energy efficient?
A: The 900 series, with its deeper frame and bigger glass package, supports higher efficiency. Both are built around 1" double-pane argon-filled Low-E tempered glass, and both carry the engineered thermal break.
Q: Do I need the 900 series?
A: It depends on your opening size and efficiency goals. A deeper, stiffer frame helps on large or high-performance openings; slimmer 798 is fine on standard lighter bays.
Q: Can I see both series before choosing?
A: Yes. Visit any of our 4 DFW showrooms or book a walkthrough and a consultant will show how each frame profile fits your openings and glass requirements.
Q: Where can I get series pricing in DFW?
A: Contact Love That Door and review the aluminum window options — a consultant can size both series to your home and give you an exact quote.