The r values of most steel and fiberglass clad entry doors range from r 5 to r 6 excluding a window.
High r value exterior doors.
Feather river doors 63 5 in x81 625in mission pointe zinc 3 4 oval lt unfinished smooth right hd fiberglass prehung front door w sidelights model 182191 3a4 70.
A 2 1 4 inch solid core wooden door for example has an r value of 3 70.
Based on astm c518 calculation method the door has an r value of up to 11 but using astm c1363 tested operable the same door only have an r value of up to 3 5.
R values climb as thickness of the material increases.
Some of the features that help therma tru doors earn their energy star qualified ratings include.
This is a huge difference and essentially comes down to astm c518 being a theoretical maximum based on a steady state thermal test of only a portion of the door panel.
Therma tru fiberglass doors have a solid polyurethane foam core which is among the most energy efficient door materials available today.
A polyurethane foam core.
Look for a door with a good insulation value say a u value of at least 0 2 that is r 5 metric.
Glass inserts also cut the door s insulating value though double or triple panel glass reduces that effect.
European manufacturers of passivhaus certified doors advertise r values as high as r 11.
When determining how much insulation you need don t guesstimate calculate.
For example a 1 1 2 inch 3 81 cm thick door without a window offers more than five times the insulating value of a solid wood door of the same size.
In new homes especially in cold climates in very energy efficient buildings look for the best performance doors possible.
R value measures how well certain building insulation materials can resist heat.
The higher the r value the greater the insulation performance.
Rustica s french style sliding barn doors entry doors and rustica s replacement windows have the most efficient r value on the market listed at 3 94 for interior doors and replacement windows and 5 31 for a 2 1 4 exterior door.
The r value of a 1 3 4 inch wood door is 3 03.
Most therma tru decorative as well as privacy and textured glass is triple pane for reduced heat flow.