Quick answer. The symptom does not on its own establish the correct replacement weatherstrip or a single proven failure. Observe the exact joint and normal closing behavior before replacing a part; if there is a building-water path, alignment problem or safety-rated assembly, obtain model-specific service guidance.
The answer is not automatically a new gasket
A casement closes against a frame and commonly relies on compression seals, but a cold hinge-side corner does not prove the seal is undersized or failed. DOE describes casement/awning compression closure as a different operating type from sliding windows; it does not identify the specific gasket in your sash. [DOE_TYPES]
Identify the corner precisely
Photograph the inside corner with the sash fully closed in its normal configuration, and again at a safe small opening only if the operating hardware is sound. On paper, distinguish hinge-side vertical seal, adjacent head/sill seal, and meeting point where those run into one another. Record whether the symptom is near the glass edge, corner gasket, hinge, or trim. Look for a kink, displaced corner joint, foreign matter on the closure face or daylight — without scraping the channel.
Compare closure, not just foam size
Check whether the sash closes freely, whether its edge remains approximately parallel to the frame and whether all normal locking points engage. Uneven gap or unusual resistance is a hardware or alignment question before it is a weatherstrip shopping question. Never force the operating crank or change hinge positions simply to obtain more seal compression. A repeated cool sensation with no demonstrable air passage remains unresolved, rather than confirming an OEM defect.
Write down the geometry
For a safely accessible already-removed strip, document the base/foot and retaining groove first, then profile reach in the relaxed state. Record both hinge-corner and center-side positions if accessible by observation. Do not call flattened installed height the original design height, and do not recommend a thicker substitute without the manufacturer's operating-clearance specification.
Do not confuse caulked joints
NPS distinguishes stationary frame-to-wall caulk from moving sash weatherstripping. Caulk across an operable hinge or sash contact can stop movement, obstruct drainage and hide the problem rather than establish fit. Preserve any existing drainage opening. [NPS_AIR]
Escalation questions
Ask the window manufacturer or service technician: What is the series and sash revision? Which portion of the hinge corner should actually contact its seal? What photos and datum measurements identify the correct part? Is hardware adjustment required before gasket evaluation? If a hinge is loose, sash is heavy, or escape opening affected, stop self-adjustment and seek qualified help.
Bounded source notes (checked publisher web pages; 2026-10-12)
- [DOE_TYPES] U.S. Department of Energy, Window Types and Technologies, Energy Saver web page, published 2012-06-18, reviewed 2026-10-12; locator: Operating Types: casement compression, sliding operation and differing leakage patterns. https://www.energy.gov/energysaver/window-types-and-technologies (Scope: Comparative generic observation, not fit evidence for the reader’s assembly)
- [NPS_AIR] U.S. National Park Service, Weatherization of Historic Buildings: Eliminate Air Infiltration, Updated 2022-04-11; reviewed 2026-10-12; locator: Air infiltration; caulking frame-to-wall versus weatherstripping moving sash and jamb. https://www.nps.gov/articles/000/weatherization-of-historic-buildings-air-infiltration.htm (Scope: General distinction, not permission to seal a particular window or approved installation)
- [DOE_AUDIT] U.S. National Park Service, Weatherization of Historic Buildings: Conduct an Energy Audit, NPS web article, retrieved 2026-10-12; locator: Inspect windows and doors for air leaks; draft/airflow assessment section. https://www.nps.gov/articles/000/weatherization-of-historic-buildings-energy-audit.htm (Scope: Building-level diagnostic observations; not an exact part identity or quantitative leakage measurement)