🔁 Switching from THERM
A migration guide for LBNL THERM users: what maps to what, how to bring your THMX files over, and what ThermX adds.
What Stays the Same
ThermX solves the same problem the same way: 2D steady-state heat conduction in building details with the Finite Element Method, materials defined by conductivity, and convective / fixed-temperature / adiabatic boundary conditions. Your modelling intuition transfers directly — you draw regions, assign materials, tag edges with boundary conditions, mesh and solve. And your files come with you: ThermX reads and writes THMX.
Concept Mapping: THERM → ThermX
| THERM | ThermX | Notes |
|---|---|---|
| Polygons | Regions | Drawn with polygon/rectangle tools; boolean union, subtract and split; layers and groups on top. |
| Material Library (Libraries → Material Library) | Materials panel | 37+ built-in materials with EN ISO 10456 conductivities, plus custom materials. Imported THMX materials keep name, conductivity, emissivity and color. |
| Boundary Condition Library | Boundary Conditions panel | Convective, fixed temperature and adiabatic types, with CEN and NFRC preset libraries. |
| Mesh Parameter / mesh level | Meshing panel | THERM's quadtree mesher is replaced by Delaunay triangulation with Ruppert refinement; min/max edge length and quality controls, live preview. |
| U-factor tags | U-factor panel (Results) | Select boundary surfaces to include; U computed per ISO 15099. |
| Show results / Temperature, Flux views | Results panel | Temperature map, isotherms, flux vectors — plus ψ-value (EN ISO 10211) and fRsi (EN ISO 13788) built in. |
| DXF underlay | DXF/DWG import | Imported DXF/DWG entities become editable regions, not just a tracing underlay. |
| Print report | Sheets tab → PDF export | Layout viewports, dimensions, tables and a title block, exported as vector PDF. |
| THM / THMX files | THMX import/export + native .therm.json | THMX is fully supported for exchange; the native format stores the complete project (sheets, groups, display settings). |
| CMA spacers / dividers | CMA THMX import | CMA files import as models; the WINDOW-integrated certification workflow itself stays in THERM/WINDOW. |
THMX Import Walkthrough
- File → Import THMX and pick your
.thmxfile. ThermX parses the header (title, units), materials, boundary conditions, polygons, BC assignments and mesh control settings. - Check materials. Imported materials arrive with THERM's name, conductivity, emissivity and color. Verify conductivities against your source data, or remap regions to the built-in EN ISO 10456 materials if you prefer library values.
- Check boundary conditions. Types (convective / fixed / adiabatic), film coefficients and temperatures are imported per edge. Confirm the assignments visually — BC edges are color-coded with a legend.
- Re-mesh. ThermX generates its own triangulation; THERM's mesh is not reused. Open the Meshing panel, generate, and refine until results are mesh-independent.
- Solve and compare. Run the solver and compare U-factors and surface temperatures with your THERM results. Small differences are expected from the different mesher and element discretization; investigate anything beyond a fraction of a percent — it is usually a BC or material mismatch.
- Save as .therm.json. Keep the native format for day-to-day work (it stores sheets, groups and display settings that THMX cannot), and File → Export THMX whenever a collaborator needs a THERM-compatible file.
THMX import covers geometry, materials, boundary conditions and mesh settings — but a THERM project is more than its file. THERM-specific result overlays, the mesh itself, and WINDOW-linked glazing-system data are not carried over; re-mesh and re-solve in ThermX. For NFRC certification submissions, stay in THERM/WINDOW — that workflow is defined around LBNL tools. If a particular file imports incorrectly, send it to us; THMX edge cases get fixed quickly.
You do not need to convert anything up front. ThermX opens THMX directly, so keep your library as-is and import files when a project needs them. Save to .therm.json once you start editing a detail in ThermX — and since the native format is plain JSON, your converted library stays scriptable and diffable.
What ThermX Adds
- CEN/EN ISO methods built in — ψ-value per EN ISO 10211 with the Component Editor, fRsi per EN ISO 13788 with automatic critical-point marking, EN ISO 10211 Annex A validation cases. No spreadsheet post-processing.
- Cross-platform — native Windows, macOS and Linux apps (3–7 MB installers), one license.
- Browser version — the full app at thermx.modeltok.com, including WebGPU-accelerated solving.
- Modern editor — boolean operations, snap-to-grid, layers/groups, DXF and DWG geometry import/export.
- Drawing sheets — viewports, dimensions and title blocks exported to vector PDF.
For a side-by-side feature table, see ThermX vs THERM. To put the EN ISO workflows into practice, start with the tutorials.
ThermX costs €10 one-time. Download for Windows, macOS or Linux — or open it in your browser and import a THMX file right now.