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A balcony window quotation can look complete while leaving the most important question unanswered: where do the panels go when the window opens? For a developer, contractor or purchasing team, the answer affects the usable opening, track depth, cleaning access and surrounding finishes. Comparing the C2 and C3 series is therefore most useful as a comparison of complete panel arrangements, with each proposal drawn against the same opening.

The C2 120/130 Thermal Break Lift and Sliding Window is presented around panoramic glazing and a possible hidden-frame arrangement. The C3 138 Thermal Break Sliding Window lists a five-track system, a double-rail double-pulley design and stainless-steel insect mesh. These features establish different starting points for an enquiry. The next step is to turn each into a proposal that the installer and future operator can understand.

Ask for an opening diagram, not just an elevation

Start with a common elevation showing the overall finished opening and the preferred positions of visible vertical members. Ask each proposal to identify every fixed panel, moving panel and screen. Then request a second drawing showing the fully open position. This reveals where panels overlap and how much of the opening remains available when the window is in use. A wide area of glass does not automatically mean the same width can be opened.

For the C2, ask the supplier to demonstrate the lift-and-slide operating sequence for the quoted hardware. For the C3, request the panel order across all five tracks and show which components travel on each track. Keep those descriptions attached to the quotation rather than relying on the series name. Two packages with different panel counts can produce noticeably different views and operating routines even when their overall dimensions match.

Compare the closed junction and the usable sill space

The C2 description highlights composite sealing strips at the upper and lower tracks. Ask for sections showing those junctions in the proposed configuration, including how the closed sash engages with them. The C3's multiple tracks make the sill arrangement another useful comparison point. Request the full frame depth and the positions of the tracks, drainage outlets and interior finish line. Do not infer these dimensions from the numbers in a series name.

Put both sections into the balcony wall detail. Show the floor build-up, waterproofing junction, exterior finish and any interior ledge so the relevant trades can agree their interfaces. Clarify how water is intended to leave the frame and which surfaces must remain accessible. If the project needs a particular weather-performance level, include that requirement in the enquiry and request evidence for the proposed size and assembly.

Give the screen its own position in the comparison

The C3 lists 304 stainless-steel mesh. That makes the screen a specific component to include in the operating drawing, rather than a note added after the glazing layout is approved. Ask where it sits when the glass is closed, where it moves during ventilation and how it is reached for cleaning. Its position may affect the available view and the sequence in which panels are opened.

Where the C2 proposal also needs insect screening, ask the supplier to identify the screen system explicitly. Compare the quoted arrangements on the same basis: screen coverage, handle access and the clear space left when open. Keep any required guarding separate from insect-screen selection. A mesh specification by itself should not be used to decide how a floor-to-ceiling opening meets the project's guarding requirements.

Use a sample to compare operation and maintenance

A hardware demonstration can answer questions that a rendering cannot. Ask the operator to move the proposed sash through its full travel, close it and engage the lock. Use a representative size and glazing weight where practical. Record the handle position and discuss who will use it. If a sample is smaller than the ordered units, ask the supplier to explain how the operation will differ at the final dimensions.

During the same review, inspect how the tracks can be cleaned and how wear parts are accessed. Ask which rollers, seals and handles are replaceable, how they are identified and what access is needed for replacement. For a multi-unit project, a clear parts reference linked to each window type can prevent future maintenance teams from ordering by appearance. Include the required care instructions in the handover package.

Keep optional functions visible in the final price

The C3 description includes an optional handrail platform and extendable clothes rack. If either is relevant to a residential balcony, request a separate description and drawing showing its position, attachments and interaction with moving panels. Let the project designer review that arrangement. If those options are not required, have the quotation say so; a comparison is clearer when both suppliers price the same agreed scope.

Finish with a side-by-side schedule covering panel layout, clear opening, frame depth, glazing, screen, hardware, finishes and installation interfaces. Mark the approved drawing revision and any outstanding sample decisions. The C2 may be the starting point for a lift-and-slide panoramic arrangement, while the C3 may suit an enquiry centred on its five-track and mesh configuration. The purchasing decision should follow the completed proposal, with the operating sequence and installation detail already resolved.