diff --git a/ogstools/feflowlib/_feflowlib.py b/ogstools/feflowlib/_feflowlib.py
index b0334d8af073dd76aece14ac93d8e70e4b41fccb..921870f599f31433dba8b59a7dcdb4696c393645 100644
--- a/ogstools/feflowlib/_feflowlib.py
+++ b/ogstools/feflowlib/_feflowlib.py
@@ -244,8 +244,10 @@ def _convert_to_SI_units(mesh: pv.UnstructuredGrid):
             for to_be_converted in arrays_to_be_converted
         ):
             mesh[data] *= 1 / 86400
-        if "4TH" in data or "2ND" in data:
+        elif "4TH" in data or "2ND" in data:
             mesh[data] *= -1 / 86400
+        elif "HEAT" in data or "TEMP" in data:
+            mesh[data] = mesh[data] + [273.15] * len(mesh[data])
     return mesh
 
 
diff --git a/ogstools/feflowlib/tools.py b/ogstools/feflowlib/tools.py
index 67e0e04984b060f7ab5c7d15ab6a0f4360b5a1de..2a879d6bc6dd7811788b276ed5da036f1e497686 100644
--- a/ogstools/feflowlib/tools.py
+++ b/ogstools/feflowlib/tools.py
@@ -478,7 +478,7 @@ def materials_in_HT(
             phase_type="AqueousLiquid",
             name="viscosity",
             type="Constant",
-            value=1,
+            value=0.001124,
         )
         model.media.add_property(
             medium_id=material_id,