THERM 6.3: Knowledge Base 

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Last update:03/11/15 11:04 AM

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Minimum computer requirements:

bullet Pentium class or better.
bullet At least 64 MB of random access memory (RAM). For optimal operation, 128 MB or more of RAM is preferrable.
bullet Microsoft Windows 98TM, Windows 2000TM, Windows METM,  Windows NTTM.or Windows XPTM
(The program WILL NOT run with Windows 3.1TM,  Windows NT 3.51TM or Windows 95TM). 
bullet Hard disk drive with at least 40 MB of available disk space
bullet Printer supported by Microsoft Windows (serial, parallel, or shared over a network).

Installation Problems 
In order to install the program with the Microsoft NT (4.0), 2000, and XP, you must be Administrator or part of the Administrators Group on your machine. To check if you are Administrator, do the following:

bullet Go to Control Panel, then "Users and Password" in Microsoft 2000, or "User Accounts" in Microsoft XP
bullet Find the current username (yours) and look in the group column. It should say: Administrators
bullet If the current username does NOT say Administrators, contact your IT department to become Administrator, or to have someone with Administrator privileges install the program on the machine.


Projected Frame Dimension:
There are 2 new options for the projected dimension for U-factors:

bullet Projected in Glass Plane
bullet Custom Rotation

If there is a glazing system in the THERM file, Projected in Glass Plane is now the default. This allows you to rotate the glazing system without changing the U-factor, other than artifacts of the mesh since the mesh works on a 90 degree grid. Custom Rotation allows you to project the U-factor lengths onto an arbitrary angle from vertical. This currently requires a recalculation to update the results

Material Library -- General Building Materials
LBNL has made a Material Library that has more general building materials, which can be used when modeling cross-sections other than fenestration systems. Click here to download a zip file which contains this library (Material-Arch), which is called Unzip the Material-Arch.lib file from the zip file, put it in the THERM 'lib" directory (where this is depends on your operating system, see Window7 / Vista Issues), and then in THERM, from the Material Library (accessed from Libraries / Material Library) click the Load Lib button to load it into the program and use it.

For the Microsoft Windows 7 operating system

Boundary Condition Library -- Walls, Floors, Ceilings
LBNL has made a Boundary Condition Library with entries for horizontal and vertical interior and exterior surfaces, such as walls, floors and ceilings, that can be used for modeling cross-sections other than fenestration systems. The Boundary Conditions are based on the ASHRAE 2009 Handbook of Fundamentals, Chapter 26, Table 1. Surface Conductances and Resistances for Air. Download the zip file called, and unzip it into the THERM "lib" directory (where this is depends on your operating system, see  Window7 / Vista Issues), and then in THERM, from the Boundary Condition Library (accessed from Libraries/Boundary Conditions" click on the Load Lib button to load it into the program and use it.




The THERM6.3 / WINDOW 6.3 NFRC Simulation Manual is available in PDF format from this website. It contains much more detailed information about NFRC modeling rules than this FAQ.

Updated Boundary Condition Library: 
A few changes have been made to the THERM 6 Boundary Condition Library:

The Interior Frame Boundary Conditions for 20 Degree Tilt cases were wrong in the THERM 5 program, and also initial releases of THERM 6. The current release of THERM 6 has the correct values in the BC.LIB file.

Here is a comparison of the old (wrong) and new (correct) values:

Boundary Condition Name


Convective Film Coefficient (hc) W/m2K


Convective Film Coefficient (hc) W/m2K

Interior (20 Tilt) Wood/Vinyl Frame (convection only) 3.38 3.09
Interior (20 Tilt) Thermally Broken Aluminum Frame (convection only) 4.38 4.09
Interior (20 Tilt) Thermally Improved Aluminum Frame (convection only) 4.60 4.32
Interior (20 Tilt) Aluminum Frame (convection only) 4.94 4.65 (click to download) contains the new corrected values for these Boundary Conditions in a file called BC-T6-20TiltFix-CMA.lib. You can keep that name, and use the "Load" feature in the Boundary Condition Library to get the new values, or you can rename it to BC.LIB and put it in the appropriate directory (depending on your operating system) and overwrite your old (wrong) BC.LIB. Which method you choose will depend on whether you have made custom boundary conditions in your existing BC.LIB that would get overwritten if you replaced that BC.LIB with the new one.

U-factor Tag Library for CMAST Program
Click here to downlad, which contains the file "UFactor.lib", which contains a U-factor tag called "Spacer" which can be used in the CMAST program. Copy this file into the "Lib" folder of the THERM 6 directory. The location of this folder will depend on your operating system. For XP, this folder is located in C:\Program Files\LBNL\THERM6\Lib. For Windows 7, see this article about THERM file locations. This file is contained in THERM 6 installs starting with version 6.3.18, dated 12/13/2010.


Migrating WINDOW 5 databases to WINDOW 6
There are a few things to be aware of when migrating databases from WINDOW 5 to WINDOW 6. See this PowerPoint presentation from a training session about this issue.


Detailed Radiation Model for Frame Cavities Disabled
The Detailed Radiation Model choice for frame cavities has been disabled because the calculation was being done incorrectly. This feature will be added back to the program at some point in the future.

In addition, a Detailed Radiation Model for frame cavities is not defined in the CEN procedures, so even when we add detailed radiation back to frame cavities, it will only apply to the ISO15099 frame cavity model.


Automatic Radiation Enclosure: 
THERM 5.0 now has a feature that allows the radiation enclosure model to be activated without actually drawing the radiation enclosure geometry. When WINDOW 5 glazing systems are imported into a THERM file, at the bottom of the Insert Glazing System dialog box, the Interior Boundary Condition can be set to "Use convection plus enclosure radiation". When this choice is selected, and the boundary conditions are generated for the glazing system, double clicking on a boundary condition segment will show a Radiation Model setting of "AutoEnclosure". This means that the program will model a radiation enclosure that includes all the boundary segments that have this setting. It is also possible to change the Radiation Model setting after boundary conditions have been generated by going into the Boundary Condition Library (either from the Library menu or by double clicking on a boundary condition segment and clicking on the Boundary Condition Library button), and change the Radiation Model to "AutoEnclosure" if it is set to "Manual Enclosure Model". The Boundary Condition Model field must be set to "Comprehensive" in order for the Radiation Model choices to be active. The "AutoEnclosure" feature includes the same features as the "Manual Enclosure Model" which are:

bullet THERM automatically sets the film coefficients for boundary conditions inside a radiation enclosure, so these values no longer need to be calculated by hand.
bullet If multiple glazing options are defined, THERM automatically changes the interior film coefficients for each file and simulation.

Combined U-factor and Condensation Resistance Calculations: 
If the Condensation Resistance model is activated, either at the time a glazing system is imported, or later (using the Options menu, Preferences menu choice, THERM File Options tab), THERM 5.0 will automatically calculate both the U-factor and CI results in one run, and store the results for both in the same file. At the time of the simulation, the program will first run the U-factor simulation, and then automatically run the Condensation Resistance calculation (you will see in the status bar that a temporary file is created, which is the THERM file name with "_ci" appended to it.) It is possible to toggle between viewing each set of runs in the Calculation menu, Display Options menu choice -- when the Condensation Resistance results are available, there will be two radio buttons at the bottom of the screen, one for each set of results.

If you want to run only the U-factor results, simply turn off the CI option by unchecking the "Use CI Model for Glazing Systems" in the Options menu, Preferences menu choice, THERM File Options tab.

NOTE: THERM will not perform the Condensation Resistance simulation for vertical components, such as Jambs, Vertical Meeting Rails or Vertical Dividers. The following message will be displayed 

Gas Library: THERM 5.0 now saves the gas properties in the THERM file, so that it is not necessary to first import them into the THERM Gas Library from the WINDOW 5 Gas Library. They function in a similar manner to the Boundary Condition and Material Libraries in they are added to the Gas Library when the file is opened, and are saved with the file when the file is closed.

Gravity Arrow: From the View menu, select Gravity Arrow, to see a graphic representation of the gravity vector the program is using for the simulation, relative to the computer screen. This gravity vector is based on the Cross Section Type set in the File/Properties menu, as well as the direction the glazing system is imported (except for Cross Section Type = Jamb, which will always have the gravity arrow pointing into the computer screen) 

Glazing System Feedback: More information about the WINDOW 5 glazing system has been added to the Glazing System Info screen, such as individual glazing layer and gap information. Double click on a glazing system to view this information.


Array Overflow in Mesher:
When the Quad Tree Mesh Parameter (set in Options/Preferences/Therm File Options) is set too high (usually greater than 9), THERM will display the following message:

To fix this problem, set the Quad Tree Mesh Parameter to a lower number in Options/Preferences/Therm File Options. You may have to simplify your geometry in order for the model to mesh.

Boundary Condition U-factor Tags:
Always check the interior boundary condition U-factor tags to make sure that they are set correctly. THERM will assign them correctly in most cases, but there are some situations where they will not be generated correctly automatically. The two circumstances where this can happen are:

bullet When selecting all the boundary conditions on the interior of the model, and assigning them to the same boundary condition, the program will assign the U-factor tags to "None" for all these boundary conditions.
bullet If there is no "Frame" segment on the glazing system, the program will not assign the U-factor tags correctly. Frame will get assigned to the Edge area, and Edge will get assigned to the None area.

Boundary Conditions Error Message -- Inconsistent boundary condition data:
THERM will give an error message if triangular Frame Cavities are defined:

The solution is to add at least one more point in the frame cavity and move it to make a 4th surface in the frame cavity

Boundary Conditions from older WINDOW5 glazing systems:
If you open a file that has a glazing system in it with "old-style" combined boundary conditions, and you delete the glazing system, and reimport a new WINDOW5 glazing system with the same name (that has the new boundary condition settings in the glazing system import screen), THERM will not use the new ones, but instead will use the old ones. The solution is to delete the glazing system, delete the boundary conditions, save and close the file, reopen the file, then import the glazing system.

Boundary Conditions that are not set to AutoEnclosure: 
For files made with THERM 5.0 Beta 2 and glazing systems imported from WINDOW 5.01 Beta, the Radiation Model in the boundary conditions (in almost all cases these boundary conditions will be the glazing system boundary conditions imported from WINDOW 5) will probably be set to "Enclosure". This can be changed to the "AutoEnclosure" setting by going into the Boundary Condition Library and editing the boundary condition. In the Radiation section of the Boundary Conditions definition, click on the "Automatic Enclosure Model" and that change will then be reflected in all the boundary condition segments that are set to this boundary condition.

Calculation does not work -- "Trouble opening file:" message appears

This may occur the first time you try to do a calculation after installing the program. When you press the Calculate button, a message appears saying "Trouble opening file" but is otherwise blank and does not say what file is causing the problem. It is probably due to the fact that you do not have Administrator privileges on your computer which will allow the program to create the SIM directory (a subdirectory of the THERM directory which contains intermediate files created during the calculation) the first time a simulation is run, where it will write temporary files created during simulations. The solution is to either become Administrator on your computer, or reinstall the computer in a location where you do have write priveleges, so that the SIM directory can be created by THERM and intermediate files can be written to that directory.

Check Gravity Vector on Condensation Resistance Files Before Simulating:  
Use the View/Gravity Arrow feature to make sure that the gravity vector is pointing in the correct direction in files that are to be used to calculate the Condensation Resistance values. The gravity vectors should be the following:

Cross Section Type
File/Preferences Setting
File orientation Gravity Vector Orientation
Sill glazing system pointing up pointing down
Head glazing system pointing down pointing down
Head glazing system pointing up pointing up
Jamb glazing system pointing up pointing into the screen, ie, you will see what looks like an X
Meeting Rail (vertical)
such as for a horizontal slider
glazing systems pointing up and down pointing into the screen, ie, you will see what looks like an X
Meeting Rail (horizontal)
such as for a vertical slider
glazing systems pointing up and down pointing down
Divider (vertical) glazing systems pointing up and down pointing into the screen, ie, you will see what looks like an X
Divider (horizontal) glazing systems pointing up and down pointing down

An indication that something may be wrong in the Condensation Resistance (CR) calculation is if the gravity vector is not set according to the table above. Also check the temperatures and "sides" of the CR boundary conditions inside the glazing system cavity (by double clicking on them) to make sure that "Left" is really the left side of the cavity and "Right" is the right side of the cavity, and that the temperature settings make sense. If either or both the sides or the temperatures are wrong, delete the glazing system, check to make sure the File/Properties Cross Section Type is set correctly, realign the gravity vector, and reimport the glazing system.

Combined  Condensation Resistance and U-factor Calculations: 
Before simulating a file that has the Condensation Model activated (ie, there are red boundary conditions inside the glazing system), go to the Options menu, Preferences menu choice, THERM File Options tab and make sure the checkbox labeled "Use CI Model for Glazing Systems" is checked. In some instances, even though the glazing system was imported with the Condensation Resistance model turned on, and there are red boundary conditions in the glazing system cavity, the "Use CI Model for Glazing Systems" box will NOT be checked in the Options/Preferences/THERM File Options tab. This will be fixed in future versions so that this step is not necessary.

Condensation Resistance Calculations in WINDOW 5:  
In WINDOW5, in order to do correct condensation resistance calculations and use the temperature map feature, the WINDOW 5.0 program requires files in the Frame and Divider Libraries that were generated with either THERM version 5.1 (version 5.1.00) or 5.2 (5.2.04).

Condensation Resistance Calculation Error Message in WINDOW 5
If you get the following message in the WINDOW Window Library when doing a calculation, you need to recalculate the file in THERM, setting the Preferences as listed below:

In order for WINDOW to calculate the Condensation Resistance in the Window Library, you must have the following Preference set in THERM:

Crash due to "." in filename: 
We advise not using the period "." in filenames, as it can cause the program to crash in some circumstances (it can cause glazing system boundary conditions to be undefined, which will lead to the program crashing upon simulation).

Glazing Systems: 
Although THERM 5.1 can read files with WINDOW 4.1 glazing systems in them, you are strongly advised to create that glazing system in WINDOW 5.1 and reimport it into the THERM 5.1 file. If this is not done, there is no guarantee that THERM 5.1 will be able to generate the appropriate boundary conditions, or calculate the correct result.

Importing THERM file into WINDOW generates "unnamed file has a bad format" error message: 
If importing a file into WINDOW generates the error message:

"Unnamed file has a bad format"

this means that there is a problem with the THERM file, in that the file results are spanning a buffer when being read. One work around to try is to add comments to one of the input fields in the File/Properties menu -- it shouldn't take more than 15 characters.

Material Library Update: 
The Material Library has been updated (with THERM 5.2) to match the NFRC 101-2001 Procedure for Determining Thermo-Physical Properties of Materials for Use in NFRC-Approved Software Programs. 

bullet View the NFRC technical documents (go to the NFRC 101-2006 or 101-2001 link on this page
bullet Download updated Material.lib file (dated 3/18/2003 -- included in current THERM 5 installations) -- This file should be put in the THERM program directory (c:\Program Files\LBNL\WINDOW). Rename your old material.lib if you want to prevent it from being overwritten by this updated version.

Mesh Error -- Mesh appears to have gaps: 

After a simulation, if the program displays the Warning message below that "the mesh appears to have gaps", it means that one or more polygons have not been meshed properly. It is necessary to find the polygon that has not meshed (turn on the mesh display from the Calculation/Display Options menu, and select "Finite Element Mesh"). You should see one or more polygons that do not have a mesh drawn in them.


Delete the unmeshed polygons and redraw them, changing the position (even very slightly) of one point. Regenerate the boundary conditions and resimulate the problem. Changing the position of a point should solve the problem.

Migrating Files from THERM 5.2 –6.3

Reassign Exterior BCs before simulating
THERM will automatically regenerate the BCs (based on option 2, the way that they are defined) the first time a THERM 5 file is simulated in THERM 6.
Change all frame cavities to Frame Cavity NFRC 100 (from 100-2001) –use Edit/Select Special. (and also for Slightly ventilated).
Change materials if using new newnfrc-material.lib
Re-simulate all files migrated from THERM 5 to THERM 6 –jambs, meeting rails, etc will have slightly different values due to the ISO Jamb Cavity radiation fix.

Nominal Thickness:
THERM 5 is shipped with the nominal thickness settings from the NFRC 100-2002 standards document, which are different from the THERM 2.1a settings.

Print and Print Preview Does Not Show A Model

There are some circumstances where the Print or Print Preview options do not produce a picture of the THERM model. Instead you just get a blank page with a header on it.

The most likely cause for this problem is that the model is very small relative to the size of the drawing, and so it is just an invisible speck on the paper.

One way to fix this problem is to select the entire model (Edit/Select All), then copy (Edit/Copy) this model and paste it into a new model (File/New, then Edit/Paste). Then do a Print Preview (File/Print Preview) and see if the model appears.

You can see that the "drawing size" is most likely the problem -- in one example, where the model did not appear in Print Preview, the drawing size (Options/Preferences/Drawing Options) was 14884 mm hight x 18678 mm wide, while the actual model was 247 mm high and 67 mm wide. After copying the model into a new document, the drawing size was 500 mm x 500 mm, and the model image appeared in the Print Preview.


Changing the drawing size in the original drawing to a more reasonable size does not "stick" -- the program reverts back to the large size, or close to it.

One possible cause of the large drawing size is to use a DXF as an underlay that is very large. So one prevention measure would be to use an appropriately sized DXF file.

Program Crashes when Zooming with Windows 95 or Windows 98 Operating Systems:
If the program is crashing when you use the Zoom feature, go to Options/Preferences and "check" the "Windows 95" box. This should solve the problem. 

If this is happening even when you reduce the Mesh Parameter, go to Options/Preferences/Simulation, and make sure that the "Automatically increment mesh parameter" is turned OFF, ie, "unchecked". If this option is checked, the program will keep increasing the mesh parameter automatically until it can either simulate the problem or the array overflow occurs, even if you reset the mesh parameter to a smaller number. 

Report Does Not Print

THERM needs the file RICHTX32.OCX in order for the Report feature to work. This file is used by many programs so it may already be installed on your computer, and THERM will display the Report properly. However, if the Report button doesn't display anything, you need to the following:

Download the RICHTX32.ocx file by clicking here.

and save or copy it into your system directory. The standard system directories for the various versions of MS Windows are listed below:

For MS Windows 7, 32 bit computers:

copy file into c:\windows\system32

For MS Windows Windows 7, 64 bit computers:

copy file into c:\windows\syswow64

You also need to "register" the file. Click here for complete instructions about how to register the OCX file.

Steady solution is diverging in ConRad:  
If this message appears at the end of a simulation, the program will not have been able to calculate a solution to the model. Go to the Options menu, select Preferences, and go to the Simulation tab. Changing the Relaxation Parameter will probably allow the file to simulate. The default setting for Relaxation Parameter should be 1.0 and that is the setting to try first. If that does not allow the program to simulate, increment that value down in 0.01 increments until the problem simulates, without going below a value of 0.90. For example, if the problem didn't converge at 1.0, the next Relaxation Parameter to try is 0.99, then 0.98, until you reach 0.90.

Underlays with AutoCAD versions 2000 and newer:  
THERM cannot read DXF files from AutoCAD versions 2000 and newer, so in the File/Save As dialog box in either of those AutoCADversions, set the Type to either AutoCAD12 or AutoCAD13 DXF format files.

Exporting sections or parts of a file (Autocad 2000):

To prepare an AutoCAD dxf section for use in Therm, follow the steps below. Note that you may want to use only part of the drawing. You can save each section in a separate file or save the entire vertical or horizontal section in a single file.

Note that parts in a drawing may not be able to be completely exploded and may not appear in Therm. You may have to go back to the originator of the file and ask them to make sure that the parts are able to be exploded.

Whole product SHGC calculations:  
The ISO 15099 formula for the frame Solar Heat Gain Coefficient (SHGC) specifies that the surface area (Asurf) should be the outdoor wetted surface, while the frame area (Af) should be the indoor projected surface area. By default, if there are no exterior U-factor tags, THERM passes the inside wetted length to WINDOW5 for the SHGC calculation. In order for THERM to pass the exterior wetted surface length, tag the exterior frame boundary conditions with the U-factor tag of "SHGC Exterior". In the latest installation of THERM, this tag is in the default U-factor tag library, but if it is not there, you can be added to the library.

Pulldown menus don't respond under Microsoft Window 7 (Operating System):  
If the Boundary Condition and Material pulldown menus are not working under the Microsoft Window 7 operating system, do the following:

Close the THERM program.

From the Start menu (or from Explorer), get to the place where you can see the THERM program shortcut. Right click on that shortcut and select the Properties choice at the bottom of the list.

In the Properties dialog box, under Compatibility check Disable Visual Themes

Restart the THERM program and the fix should allow the pulldown lists to now work properly.



Frame Cavity Emissivities
There are some circumstances where the program will assign frame cavity surface emissivities based on the emissivities of the glazing system layers, rather than the emissivities of the surrounding surfaces. This problem occurs only with frame cavities using the advanced radiation model or the iso model, and is partly based on the geometry of the frame cavity as it relates to the glazing system. It is hard to predict when it will happen, and so the best way to make sure this is not happening in a particular file is to print out the Report for the file (File/Report), and examine the emissivities of all the frame cavities to see if there are any that do not seem to make sense.


If some questionable values are found, it is possible to then example the frame cavity in question (the Polygon ID is listed in the report in the first column, and that polygon can be selected in the THERM file by using the Edit/Select Special menu and then typing the Polygon ID number in the ID field). Once the problem polygon is selected, double click on each frame cavity surface and the emissivity of that surface will be displayed. In general, unless overridden by the user, these emissivities should be the emissivities of the materials the surface is touching. If these emissivities are found to be incorrect (if the problem is from this bug, the emissivities will be set to one of the glass layer emissivities, so it should be obvious if that is the problem), then the emissivity can be changed by inputting the correct value into this dialog box, and rerunning the file.


Boundary Conditions Changed from Comprehensive to Simplified
If a Boundary Condition is initially defined with the Model = Comprehensive in the Boundary Condition Library and applied to a cross section surface, an then is later changed to Model = Simplified in the Boundary Condition Library, if the applied boundary condition is "clicked on", the Radiation model will still be set to "AutoEnclosure" even though it shouldn't be. The solution is to make a completely new Boundary Condition with the Model = Simplified, rather than taking one that was originally defined with the Model = Comprehensive.


Boundary Condition is originally defined as Model = Comprehensive


Boundary Condition is changed to Model = Simplified


When a boundary condition segment is clicked on, the Radiation Model is still set to AutoEnclosure, even though it shouldn't be.

Two Automatic Radiation Enclosures in the Same Model
If there are two Automatic Radiation Enclosures in the same THERM cross section, the program will not necessarily calculate the results correctly. The solution until this bug is fixed is to set one set of boundary conditions to "Blackbody" and the other to "Automatic Radiation Enclosure". If you have a model where you want to do this and have questions about to set up the model, send email to

CEN Cavity Model Error -- Input data error in ConRad
Defining a Frame Cavity with the Cavity Model set to "CEN" will result in an error message "Input data error in ConRad" and the file will not run. The only solution is to change the Cavity Model to "ISO 15099".

Input Error in Conrad or "Trouble with Intermediate Files"
If you are getting the error message "Input data error in ConRad" or "Trouble with intermediate simulation files", you may want to use an updated conrad.dll file: