Heat Loss due to Transmission

Heat loss due to transmission, R-values and U-values - all in imperial units

Heat Transmission

The heat transmission through a building wall or similar construction, can be expressed as:

H_t = U A dt (1)

where

H_t = heat loss (btu/hr)

U = "U-value" (btu/hr sq. ft ^oF)

dt = temperature difference (^oF)

U and R-values

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 U-value of a construction consisting of several layers can be expressed as

U = 1 / ∑ R (2)

where

R = "R-value" - the resistance to heat flow in each layer (hr sq.ft ^oF/btu)

The R-value of the single layer can be expressed as:

R = 1 / C = 1 / K l_t (3)

where

C = layer conductance (btu/hr sq.ft ^oF)

K = layer conductivity (btu in/hr sq.ft ^oF)

l_t = thickness of layer (inches)

ToolBox ShortList

Difficult to find your favorite ToolBox page? Add a link to the page in your own personal Shortlist!

• Add this Page! • Delete the ShortList!

Translate this page to Spanish French German Italian Dutch Norwegian

The content in The HVAC ToolBox is copyrighted but can be used with NO WARRANTY or LIABILITY. Important information should always be double checked with alternative sources. All applicable national and local regulations and practices concerning this aspects must be strictly followed and adhered to.

We appreciate any comments and tips on how to make The HVAC ToolBox a better information source. Please contact us by email if You find any faults, inaccurate, or otherwise unacceptable information.

5 12 1