|Building Element||Heat-Transfer Coefficient|
|(Btu/(hr ft2 oF))||(W/(m2K))|
|Doors||Single sheet - metal||1.2||6.8|
|1 inch - wood||0.65||3.7|
|2 inches - wood||0.45||2.6|
|Roofing||Corrugated metal - uninsulated||1.5||8.5|
|1 inch wood - uninsulated||0.5||2.8|
|2 inches wood - un-insulated||0.3||1.7|
|1 inch wood - 1 inch insulation||0.2||1.1|
|2 inch wood - 1 inch insulation||0.15||0.9|
|2 inches - concrete slab||0.3||1.7|
|2 inches - concrete slab - 1 inch insulation||0.15||0.9|
|Windows||Vertical single glazed window in metal frame||5.8|
|Vertical single glazed window in wooden frame||4.7|
|Vertical double glazed window, distance between glasses 30 - 60 mm||2.8|
|Vertical triple glazed window, distance between glasses 30 - 60 mm||1.85|
|Vertical sealed double glazed window, distance between glasses 20 mm||3.0|
|Vertical sealed triple glazed window, distance between glasses 20 mm||1.9|
|Vertical sealed double glazed window with "Low-E" coatings||0.32||1.8|
|Vertical double glazed window with "Low-E" coatings and heavy gas filling||0.27||1.5|
|Vertical double glazed window with 3 plastic films ("Low-E" coated) and heavy gas filling||0.06||0.35|
|Horizontal single glass||1.4||7.9|
|Walls||6 inches (150 mm) - poured concrete 80 lb/ft3||0.7||3.9|
|10 inches (250 mm) - brick||0.36||2.0|
U-value (or U-factor) is a measure of the rate of heat loss or gain through a construction of materials. The lower the U-factor, the greater the material's resistance to heat flow and the better is the insulating value. U-value is the inverse of R-value.
The overall U-value of a construction consisting of several layers can be expressed as
U = 1 / ∑ R (2)
U = heat transfer coefficient (Btu/hr ft2 oF, W/m2K)
R = "R-value" - the resistance to heat flow in each layer (hr ft2 oF/Btu, m2K/W)
The R-value of the single layer can be expressed as:
R = 1 / C = s / k (3)
C = layer conductance (Btu/hr ft2 oF, W/m2K)
k = thermal conductivity of layer material (Btu in/hr ft2 oF, W/mK)
s = thickness of layer (inches, m)
Note! - in addition to resistance in each construction layer - there is a resistance from the inner and outer surface to the surroundings. If you want to add the surface resistance to the U calculator below - use one - 1- for thickness - lt - and the surface resistance for the conductivity - K.
This calculator can be used to calculate the overall U-value for a construction with four layers. Add the thickness - lt - and the layer conductivity - K - for each layer. For fewer than four layers, replace the thickness of one or more layers with zero.
A concrete wall with thickness 0.25 (m) and conductivity 1.7 (W/mK) is used for the default values in the calculator above. The inside and outside surface resistance is estimated to 5.8 (m2 K/W).
The U value can be calculated as
U = 1 / (1 / (5.8 m2K/W) + (0.25 m) / (1.7 W/mK))
= 3.13 W/m2K
|(hr ft2 oF/Btu)||(m2K/W)|
|Wood bevel siding 1/2" x 8", lapped||0.81||0.14|
|Wood bevel siding 3/4" x 10", lapped||1.05||0.18|
|Stucco (per inch)||0.20||0.035|
|Softboard, pine or similar 3/4"||0.94||0.17|
|Softboard, pine or similar 1 1/2"||1.89||0.33|
|Softboard, pine or similar 2 1/2"||3.12||0.55|
|Gypsum board 1/2"||0.45||0.08|
|Gypsum board 5/8"||0.56||0.1|
|Common brick per inch||0.20||0.04|
|(hr ft2 oF/Btu)||(m2K/W)|
|2 x 4 stud wall, uninsulated||5||0.88|
|2 x 4 stud wall with 3 1/2" batt insulation||15||2.6|
|2 x 4 stud wall with 1" polystyrene rigid board, 3 1/2" insulation blanket||18||3.2|
|2 x 4 stud wall with 3/4" insulation board, 3 1/2" batt insulation, 5/8" polyurethane insulation||22||3.9|
|2 x 6 stud wall with 5 1/2" insulation blanket||23||4|
|2 x 6 stud wall with 3/4" insulation board, 5 1/2" batt insulation, 5/8" polyurethane insulation||28||4.9|
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