Garage door manufacturers make doors in many different styles and materials with well written and detailed descriptions. They will always list the R-Value and U-Factor of the door prominently in the description but do little to explain what these terms actually mean. We are going to try to make it a little easier to understand for the customer that doesn’t usually deal in thermo-dynamic equations. The first thing to understand is that the higher the posted R-Value and U-Factor means the better insulating properties of the materials the garage door is constructed of and assembled with which has a direct effect on the door’s price.
Let’s first discuss what they are how they are calculated. R-value is the thermal resistance to heat flow which generally applies to specific materials or the thickness of the insulation in a garage door section. The U-factor is the measurement of thermal conduction due to heat flow through an installed door system. Of the two measurements the U-Factor will give a better representation of the insulating abilities of your fully installed garage door. Determining the R-Value of a garage door is done by measuring the heat resistance of only the door section’s materials and combined thickness. To illustrate, insulated doors have exterior and interior surfaces made of wood or steel and an insulating material that is sandwiched between them which is usually made of either polyurethane foam or expanded polystyrene foam. Each of these materials have test verified and industry accepted R-Values, which indicate their ability to resist heat transfer. Another element considered in the equation is the considerable heat dissipating effect of moving air on a vertical surface, which ANSI/DASMA (American National Standards Institute/Door and Access Systems Manufacturers Association) has termed “air film”. When tested, each has an R-value that added together create the door section’s R-Value.
The equation is as follows: The Door Section R-Value = the combined R-Values of the interior and exterior Air Films + the Outside Surface + Insulation + the Inside Surface
The U-Factor is the result of the measurement of heat transmitted through the full door assembly when using the test standard ANSI\DASMA 105 to test the heat transmitted due to heat flow of an entire installed garage door assembly. This test takes into account all of the factors that affect the installed door’s ability to resist heat transfer through the more conductive components in the door such as the door section joints which hold the door sections together, stile attachments, thermal breaks, air spaces, and weather seals. To perform the test the garage door assembly is installed according to the manufacturer’s instructions in a controlled test chamber. Then the temperature of the interior face of the door is maintained at a constant temperature and the exterior face of the door is cooled. The energy expended to sustain the interior temperature is calculated and determines the amount of heat flow (U-factor) through the complete door system.
In summary, of the two ways a garage door’s insulating abilities can be measured and stated, the R-Value of the “Calculated Door Section” and the U-Factor of the “Tested Installed Door”, the latter gives a more accurate picture of the door’s overall performance since The “Tested Installed Door” produces a result representing a complete door and the “Calculated Door Section” represents a portion of an individual door section.