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The interior air design temperature used for the winter condensation check.
The check compares the temperature of the INNER SURFACE against the dew point of the air touching it, so the room temperature matters twice: it sets one end of the temperature gradient, and with the humidity it sets the dew point the surface has to stay above. Warmer rooms are not automatically safer — a room held warmer and at the same relative humidity has a higher dew point, and the surface has to keep ahead of it.
The exterior winter design temperature for the project location, typically a 97.5% or 99% design condition.
The design condition, not the record low. A 99% winter design temperature is exceeded for about 88 hours a year, which is the basis condensation criteria are written against; designing to the coldest night ever recorded produces a facade nobody will pay for and does not reflect how the criterion is judged. Where the building has a humidified use — a swimming pool, a museum, a hospital — the relevant question is usually the humidity rather than the temperature.
The overall U-factor of the spandrel/vision glass assembly being checked.
An assembly U-factor is an AVERAGE, and condensation is a local event. The frame, the edge of the glass and any thermal bridge through the bracket are all colder than the whole-assembly figure suggests, so a wall that passes this check on its average U can still run wet at the sight line and around the perimeter. Where the margin is thin, the manufacturer's Condensation Resistance Factor or a thermal model of the actual frame answers a question the average cannot.
The interior air film coefficient, commonly taken as 8 W/m²K per standard convention.
8 W/m²K is the standard still-air value, and it assumes the room air can actually reach the glass. It cannot behind a closed blind, a heavy curtain, or a perimeter convector somebody has blocked with furniture — and the film coefficient falls with it, taking the surface temperature down with it. That is why condensation appears first behind blinds, and why a facade that models clear can still fail in occupation. Lowering this figure is how you test that case.
The dew point of the interior air, based on its temperature and relative humidity.
It comes from the room temperature and the relative humidity together, and it is the number the surface has to stay above — a room at 21 °C (70 °F) and 40% RH has a dew point near 7 °C (45 °F), while the same room at 60% RH is near 13 °C (55 °F), which is a change of six Celsius (eleven Fahrenheit) degrees in what the glass has to achieve for no change in the temperature anyone feels. On a building whose humidity is not controlled, the winter humidity is set by the occupants and their activities rather than by the design, which is why this input deserves a pessimistic value rather than a nominal one. The Dew Point and Relative Humidity Calculator works it out from the room's temperature and humidity.
Interior glass surface temperature
57.2 °F
The calculated interior glass surface temperature stays above the interior air's dew point shown below, so condensation is not predicted under these steady-state design conditions. This checks room-side vision/spandrel glass surface condensation risk only, per NFRC 500/AAMA 1503 steady-state methodology. Shadowbox CAVITY condensation — a distinct, common failure mode driven by trapped cavity moisture and solar vapor drive behind the spandrel panel — is NOT covered here and needs separate ventilation/vapor analysis per GANA/NGA guidance. No risk predicted under these conditions is not the same as none. The conditions are the ones you entered, and one surface is not the assembly.
- Interior air dew point
- 50 °F
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Curtain Wall Spandrel Condensation Risk Checker: 57.25 °F — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Steady-state condensation risk check per AAMA 1503/NFRC 500 methodology: interior surface temperature Ts = Ti − U×(Ti−To)/hi, where Ti/To are interior/exterior design temperatures, U is the assembly's overall U-factor, and hi is the interior air film coefficient (commonly 8 W/m²K); condensation risk exists if Ts falls below the interior air's dew point
Inputs used
- Interior Design Temperature
- 69.8 °F
- Exterior Winter Design Temperature
- 14 °F
- Assembly U-Factor (W/m²K)
- 1.8
- Interior Film Coefficient (W/m²K, commonly 8)
- 8
- Interior Air Dew Point
- 50 °F
Intermediate steps
- Interior air dew point
- 50 °F
Confidence note: The calculated interior glass surface temperature stays above the interior air's dew point shown below, so condensation is not predicted under these steady-state design conditions. This checks room-side vision/spandrel glass surface condensation risk only, per NFRC 500/AAMA 1503 steady-state methodology. Shadowbox CAVITY condensation — a distinct, common failure mode driven by trapped cavity moisture and solar vapor drive behind the spandrel panel — is NOT covered here and needs separate ventilation/vapor analysis per GANA/NGA guidance. No risk predicted under these conditions is not the same as none. The conditions are the ones you entered, and one surface is not the assembly.
What this calculation does not cover
- Models conduction only. Warm indoor air pushed out through an imperfect air seal — a splice joint, an anchor pocket, a gasket that has taken a set — carries far more moisture into the assembly than diffusion does, and it condenses wherever it cools rather than on the face being checked. A wall that passes on paper can still run with water, or ice, inside the mullion, and the first sign of it is usually a stain at the head of the panel below.
- Uses the exterior air temperature, and the outer surface does not sit at it. On a clear, calm night the glass radiates to the sky and settles several degrees below the surrounding air, which drags the interior surface down with it — and those are exactly the nights condensation forms. A result that clears the dew point by a degree or two at the design air temperature has no margin left for the sky.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.1.1
Regulatory standards & verification citations1
- Steady-state condensation risk check per AAMA 1503/NFRC 500 methodology: interior surface temperature Ts = Ti − U×(Ti−To)/hi, where Ti/To are interior/exterior design temperatures, U is the assembly's overall U-factor, and hi is the interior air film coefficient (commonly 8 W/m²K); condensation risk exists if Ts falls below the interior air's dew point
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