TECHNICAL INFORMATION Bulletin #01 February 2018

How to calculate “R” Values

“R” value is used to designate the parallel surfaces and means the Where r1 = uninsulated pipe radius thermal resistance of an object. R-value increases proportionally to in inches 01 The higher the R-value, the higher the thickness. r2 = insulated pipe radius in inches thermal resistance and thus, Cylindrical Objects insulating value. k = thermal conductivity The simple equation for R-value Flat Objects r does does not hold true for r ln 2 2 ( r ( R-values for flat objects such as cylindrical objects like pipe R= 1 for sheet insulation are easy to insulation. For these objects, k calculate. It is simply the thickness the heat flow is not the simple of the insulation in inches divided straight-through heat flow found Based on this equation, the by the thermal conductivity of the with flat objects. Instead, the heat R-value gets larger as the insulation. For example, a two flow is radial because the inner insulation thickness increases but inch thick sheet of insulation with surface area is much smaller than also as the pipe sizes gets smaller. a thermal conductivity of 0.25 outer surface area and the R-value For example, 1" thick insulation Btu•in/h•ft2•°F has an R-value calculation must take this into will have a higher R-value on a 1" equal to 2 divided by 0.25 or 8.0. account. As a result, the equation pipe than it will on a 3" pipe. As a for the R-value of cylindrical result, one must always consider This simple equation is true for any objects is as follows: the pipe size and insulation flat, homogeneous material with thickness to determine the R-value of insulation on a pipe.

Heat flow Heat flow

thickness

Heat flow

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00019 ArmaFlex R-Values ArmaFlex Tech Bulletin 020818 NA EN_A TB01