What is Condensation? The moisture that appears on the window surface as water when temperatures are above freezing, and as frost when temperatures are below freezing, is termed condensation. Condensation occurs when the temperature of any surface falls below the dew point. The dew point constantly changes with the air temperature and relative humidity. At any given temperature there is a maximum amount of water vapor the air can hold. When the air can no longer hold the moisture, it will deposit that moisture on any surface that falls below the temperature at the saturation pressure, or dew point. Windows are the Yardstick. The concern for condensation on windows is common during the time of the year when conditions are reaching their extremes. It is often overlooked that condensation might occur on other building substrates as well. Windows do not cause condensation, but indicate when conditions are favorable for condensation to form. Condensation is a result of temperature and humidity. Water is in our atmosphere and will condense on colder surfaces when conditions are favorable. Condensation is Undesirable. While higher humidity levels are sometimes considered more comfortable, they are not desirable for other reasons. High humidity levels can cause condensation to form on windows and doors. In addition, high humidity can increase the chance of water vapor condensing in wall and ceiling insulation, deteriorating wood framing, sheathing, and painted surfaces. While some level of condensation is acceptable, humidity levels must be moderated and controlled. How is Condensation Controlled? There are three main variables to consider when trying to control condensation: 1) the exterior temperature, 2) the interior temperature, and 3) the inside relative humidity. The inside temperature and the interior humidity are the things we have control over. Managing Condensation. EFCO Corporation is a material supplier for fenestration products. We recommend that building design incorporate humidity control. Whether it is new construction or renovation, condensation will occur because water is in the atmosphere. Things to consider include the reduction in the humidity level and increasing air circulation around problem areas. Window coverings restrict air movement around the window which can increase the formation of condensation. If window coverings must be used, keep them open as much as possible. If the window is recessed in a wall cavity, natural air flow may not be adequate to minimize condensation, therefore a fan may be necessary to assist the air circulation. Ceiling fans can be installed to assist air flow and dehumidifiers can be used as a means of reducing humidity. If the humidity level is controlled, condensation can be managed. When Does Temporary Condensation Occur? There are some situations where condensation occurs that is temporary. New construction and remodeling will increase the probability of condensation because wood, drywall, cement and other building materials take time to cure and dry out, thus increasing moisture and humidity. During the summer, building materials absorb moisture. At the beginning of the heating season, temporary condensation can occur until the building loses the excess moisture it gains during summer months. Sharp drops in temperature can also create temporary condensation problems during the heating season due to the trapped warmer humid air inside the building. Cracking a window for a short time can help clear up condensation. The interior temperature and the interior relative humidity are the basic variables used to control condensation. Product Selection. Selecting the proper fenestration product for the geographic location, and having an understanding of the causes of condensation will make a significant difference in the success of minimizing condensation. Metal and glass surfaces have higher conductivity rates and will dissipate heat quicker than wood, cloth and other interior surfaces. Given the same relative humidity in the room, condensation will occur at window surfaces more often. Is There a Way to Select a Window for my Geographic Location? Fenestration products are usually tested to determine a Condensation Resistance Factor (CRF). The CRF is a rating obtained by standardized testing which establishes a prediction, within reasonable accuracy, of the formation of condensation of a fenestration product. EFCO Corporation publishes the CRF ratings of standard products. These CRF ratings can be obtained from the product overviews in EFCO Corporation’s product literature, or visit www.efcocorp.com. Identify your Outside Design Temperature: Identify Maximum Recommended Humidity Levels: TABLE B MAXIMUM RECOMMENDED HUMIDITY LEVELS Based on engineering studies at 70°F conducted at the University of Minnesota Laboratories. OUTSIDE AIR TEMPERATURE INSIDE RELATIVE HUMIDITY -20 Degrees F. or Below Not Over 15 Percent -20 Degrees F. to -10 Not Over 20 Percent -10 Degrees F. to 0 Not Over 25 Percent 0 Degrees F. to 10 Not Over 30 Percent 10 Degrees F. to 20 Not Over 35 Percent 20 Degrees F. to 40 Not Over 40 Percent Relative humidity levels above these are not recommended at the low outside temperatures indicated, unless special provisions are taken in building construction. If higher relative humidity levels are required because of special interior environmental conditions, the product manufacturer should be consulted. Select the Recommended CRF for the product: TABLE A MINIMUM RECOMMENDED CONDENSATION RESISTANCE FACTORS (CRF)* Inside Relative Humidity 15% 20% 25% 30% 35% 40% -20°F 46 52 57 60 - - -10°F 39 46 52 56 60 - 0°F 30 39 45 52 57 61 +10°F 17 29 37 44 50 57 +20°F 0 16 25 34 40 48 Outside Temperature *Specifications of above Resistance Factors are based upon an inside air temperature of 68°F and outside window velocity of 15 MPH. Select EFCO Corporation’s Product: Maximum Recommended Indoor Humidity at 70º Indoor Temperature EFCO® 2700 2700 Product 510 I 2900 810 I Project Outside CSMT Out Temperature 890 1325 Tilt Turn -20°F 19% 15% 23% 21% 25% 17% 27% -10°F 23% 19% 27% 26% 30% 21% 32% 0°F 28% 23% 33% 31% 35% 26% 37% +10°F 34% 30% 36% 37% 41% 32% 43% +20°F 42% 37% 46% 44% 47% 40% 50% 3450 Single Hung 660 Single Hung 690 Double Hung 6600 3500 Slider 6555 Slider 3900 -20°F 22% 16% 13% 36% 22% 25% 29% -10°F 27% 20% 17% 40% 27% 30% 33% 0°F 32% 25% 22% 45% 32% 35% 38% +10°F 38% 31% 28% 50% 38% 41% 44% +20°F 44% 38% 36% 57% 44% 47% 51% 3000 Sliding Door 3015 Sliding Door T35I 403 Storefront 960 5600 5900 -20°F 17% 18% 19% 24% 25% 33% 21% -10°F 21% 22% 24% 29% 30% 37% 26% 0°F 25% 27% 30% 34% 35% 41% 31% +10°F 31% 33% 36% 40% 41% 48% 37% +20°F 38% 40% 43% 46% 47% 55% 44% EFCO® Product Outside Temperature EFCO® Product Outside Temperature Recommendations are for design purposes only, actual building conditions will vary. This is a brief review of condensation and how it can be managed. Selecting the proper fenestration product from EFCO Corporation and designing the building with proper climate control will help manage condenstion. Information Sources: AAMA Window Selection Guide 1988, AAMA 101 /IS2-97 1999 ASHRAE Handbook HVAC Applications AAMA 1502.7, AAMA 1503.1,AAMA 1503.98 The Condensation Answer Book. Andersen Miscellaneous EFCO Corporation Historical Data.
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