In sustainable construction, one of the most proven and sought after energy reducing techniques is superinsulating in new construction or retrofitting an old building with more efficient or additional insulation.  When installed correctly, insulation is very effective in reducing energy loads on HVAC systems by keeping a more regulated and constant indoor temperature.  There are many types of insulation ranging from spray foam, to loose-fill batt, to rigid EPS, and choosing which one to use can be based on many factors.  However, the R-value of insulation takes precedent over all other factors when choosing insulation.  

An R-value is defined as a measure of a material’s ability to resist heat transfer. 
Because consumers buy insulation based on its R-value, companies who manufacture insulation must have the R-value of their product regulated by ASTM standards.  While several technical standards have been written due to specific applications of what materials are tested, a general process is common in all ASTM tests. 

The Oak Ridge National Laboratory has state of the art technologies for testing insulation and has been conducting R-value testing for over two decades.  All of their tests are now done using a hot box apparatus.  On a large scale, a hot box apparatus can fit entire mock-up wall sections into its clam shell-like chamber.  After running a test, an average rating per square foot can be assigned to any given wall section.  A Rotatable Guarded Hot Box has the ability to provide the thermal conductivity measurement in a vertical or horizontal application or any angle in between that a pitched roof may be.  On a smaller scale a hotbox apparatus can be built to test the R-value over a given square foot of insulation or sheathing material. 

How a Hotbox Apparatus Works

Two clam shell chambers hold the material to be tested in an airtight and locked position.  This creates two climate chambers, one on each side of the material, which can be regulated to steady-state conditions.  One side is designated as the metering (hot) chamber, while the other is the climate (cold) chamber.  Air is sent into each chamber and regulated by velocity and temperature of the air at the source.  The air is blown parallel to the surface of the material to prevent any convection that could occur.  Once the hot and cold side has reached a steady state the temperature of the material is measured on each side and the test begins.  The average temperature is recorded on each side of the material until the temperatures and heat flows are equilibrated.  Using the data collected the R-value is calculated using energy output of heating and cooling components, the energy exchange between the two chambers, the area of the chamber and average surface temperatures on each side.  The formula for R-value is, R= A[t1-t2]/(Qk +Qf + Qmb).  At Oak Ridge National Library, arriving at a final R-value means that two successive four hour tests have produced values within 1% of variance.

Source: Oak Ridge National Laboratory