diff --git a/src/Mod/Fem/App/FemConstraintInitialTemperature.cpp b/src/Mod/Fem/App/FemConstraintInitialTemperature.cpp
index 18a4b4c57b..a8ef1ea755 100644
--- a/src/Mod/Fem/App/FemConstraintInitialTemperature.cpp
+++ b/src/Mod/Fem/App/FemConstraintInitialTemperature.cpp
@@ -34,12 +34,16 @@ PROPERTY_SOURCE(Fem::ConstraintInitialTemperature, Fem::Constraint)
 
 ConstraintInitialTemperature::ConstraintInitialTemperature()
 {
-    ADD_PROPERTY(initialTemperature,(300.0));
+    ADD_PROPERTY(initialTemperature, (300.0));
 
-    ADD_PROPERTY_TYPE(Points,(Base::Vector3d()),"ConstraintInitialTemperature",App::PropertyType(App::Prop_ReadOnly|App::Prop_Output),
+    ADD_PROPERTY_TYPE(Points, (Base::Vector3d()),
+                      "ConstraintInitialTemperature",
+                      App::PropertyType(App::Prop_ReadOnly | App::Prop_Output),
                       "Points where symbols are drawn");
-    ADD_PROPERTY_TYPE(Normals,(Base::Vector3d()),"ConstraintInitialTemperature",App::PropertyType(App::Prop_ReadOnly|App::Prop_Output),
-                                                                             "Normals where symbols are drawn");
+    ADD_PROPERTY_TYPE(Normals, (Base::Vector3d()),
+                      "ConstraintInitialTemperature",
+                      App::PropertyType(App::Prop_ReadOnly | App::Prop_Output),
+                      "Normals where symbols are drawn");
     Points.setValues(std::vector<Base::Vector3d>());
     Normals.setValues(std::vector<Base::Vector3d>());
 
@@ -57,6 +61,19 @@ const char* ConstraintInitialTemperature::getViewProviderName() const
     return "FemGui::ViewProviderFemConstraintInitialTemperature";
 }
 
+void ConstraintInitialTemperature::handleChangedPropertyType(Base::XMLReader& reader,
+                                                             const char* TypeName,
+                                                             App::Property* prop)
+{
+    // property initialTemperature had App::PropertyFloat, was changed to App::PropertyTemperature
+    if (prop == &initialTemperature && strcmp(TypeName, "App::PropertyFloat") == 0) {
+        App::PropertyFloat initialTemperatureProperty;
+        // restore the PropertyFloat to be able to set its value
+        initialTemperatureProperty.Restore(reader);
+        initialTemperature.setValue(initialTemperatureProperty.getValue());
+    }
+}
+
 void ConstraintInitialTemperature::onChanged(const App::Property* prop)
 {
     // Note: If we call this at the end, then the arrows are not oriented correctly initially
diff --git a/src/Mod/Fem/App/FemConstraintInitialTemperature.h b/src/Mod/Fem/App/FemConstraintInitialTemperature.h
index 6cd0414b67..2bfcc7bb83 100644
--- a/src/Mod/Fem/App/FemConstraintInitialTemperature.h
+++ b/src/Mod/Fem/App/FemConstraintInitialTemperature.h
@@ -45,7 +45,7 @@ public:
     App::PropertyVectorList Normals;
 
     //Temperature parameters
-    App::PropertyFloat initialTemperature;
+    App::PropertyTemperature initialTemperature;
 
 
     /// recalculate the object
@@ -55,6 +55,8 @@ public:
     const char* getViewProviderName() const override;
 
 protected:
+    void handleChangedPropertyType(Base::XMLReader& reader, const char* TypeName,
+                                   App::Property* prop);
     void onChanged(const App::Property* prop) override;
 
 };
diff --git a/src/Mod/Fem/App/FemConstraintTemperature.cpp b/src/Mod/Fem/App/FemConstraintTemperature.cpp
index 2a990abfc7..26e8042bc6 100644
--- a/src/Mod/Fem/App/FemConstraintTemperature.cpp
+++ b/src/Mod/Fem/App/FemConstraintTemperature.cpp
@@ -36,16 +36,19 @@ static const char* ConstraintTypes[] = {"CFlux","Temperature", nullptr};
 
 ConstraintTemperature::ConstraintTemperature()
 {
-    ADD_PROPERTY(Temperature,(300.0));
-    ADD_PROPERTY(CFlux,(0.0));
-    ADD_PROPERTY_TYPE(ConstraintType,(1),"ConstraintTemperature",(App::PropertyType)(App::Prop_None),
+    ADD_PROPERTY(Temperature, (300.0));
+    ADD_PROPERTY(CFlux, (0.0));
+    ADD_PROPERTY_TYPE(ConstraintType, (1), "ConstraintTemperature",
+                      (App::PropertyType)(App::Prop_None),
                       "Type of constraint, temperature or concentrated heat flux");
     ConstraintType.setEnums(ConstraintTypes);
 
-    ADD_PROPERTY_TYPE(Points,(Base::Vector3d()),"ConstraintTemperature",App::PropertyType(App::Prop_ReadOnly|App::Prop_Output),
+    ADD_PROPERTY_TYPE(Points, (Base::Vector3d()), "ConstraintTemperature",
+                      App::PropertyType(App::Prop_ReadOnly | App::Prop_Output),
                       "Points where symbols are drawn");
-    ADD_PROPERTY_TYPE(Normals,(Base::Vector3d()),"ConstraintTemperature",App::PropertyType(App::Prop_ReadOnly|App::Prop_Output),
-                                                                             "Normals where symbols are drawn");
+    ADD_PROPERTY_TYPE(Normals, (Base::Vector3d()), "ConstraintTemperature",
+                      App::PropertyType(App::Prop_ReadOnly | App::Prop_Output),
+                      "Normals where symbols are drawn");
     Points.setValues(std::vector<Base::Vector3d>());
     Normals.setValues(std::vector<Base::Vector3d>());
 }
@@ -60,6 +63,24 @@ const char* ConstraintTemperature::getViewProviderName() const
     return "FemGui::ViewProviderFemConstraintTemperature";
 }
 
+void ConstraintTemperature::handleChangedPropertyType(Base::XMLReader& reader, const char* TypeName,
+                                                      App::Property* prop)
+{
+    // property Temperature had App::PropertyFloat and was changed to App::PropertyTemperature
+    if (prop == &Temperature && strcmp(TypeName, "App::PropertyFloat") == 0) {
+        App::PropertyFloat TemperatureProperty;
+        // restore the PropertyFloat to be able to set its value
+        TemperatureProperty.Restore(reader);
+        Temperature.setValue(TemperatureProperty.getValue());
+    }
+    // property CFlux had App::PropertyFloat and was changed to App::PropertyPower
+    else if (prop == &CFlux && strcmp(TypeName, "App::PropertyFloat") == 0) {
+        App::PropertyFloat CFluxProperty;
+        CFluxProperty.Restore(reader);
+        CFlux.setValue(CFluxProperty.getValue());
+    }
+}
+
 void ConstraintTemperature::onChanged(const App::Property* prop)
 {
     // Note: If we call this at the end, then the arrows are not oriented correctly initially
diff --git a/src/Mod/Fem/App/FemConstraintTemperature.h b/src/Mod/Fem/App/FemConstraintTemperature.h
index 38d58c0a37..c2e088f8db 100644
--- a/src/Mod/Fem/App/FemConstraintTemperature.h
+++ b/src/Mod/Fem/App/FemConstraintTemperature.h
@@ -45,8 +45,8 @@ public:
     App::PropertyVectorList Normals;
 
     //Temperature parameters
-    App::PropertyFloat Temperature;
-    App::PropertyFloat CFlux;
+    App::PropertyTemperature Temperature;
+    App::PropertyPower CFlux;
     App::PropertyEnumeration ConstraintType;
 
 
@@ -57,6 +57,8 @@ public:
     const char* getViewProviderName() const override;
 
 protected:
+    void handleChangedPropertyType(Base::XMLReader& reader, const char* TypeName,
+                                   App::Property* prop);
     void onChanged(const App::Property* prop) override;
 
 };
diff --git a/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.cpp b/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.cpp
index 0ca79fe1f6..93d06efda6 100644
--- a/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.cpp
+++ b/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.cpp
@@ -60,21 +60,17 @@ TaskFemConstraintInitialTemperature::TaskFemConstraintInitialTemperature(
     std::vector<std::string> SubElements = pcConstraint->References.getSubValues();
 
     // Fill data into dialog elements
-    ui->if_temperature->setMinimum(0);
-    ui->if_temperature->setMaximum(FLOAT_MAX);
-    Base::Quantity t =
-        Base::Quantity(pcConstraint->initialTemperature.getValue(), Base::Unit::Temperature);
-    ui->if_temperature->setValue(t);
+    ui->if_temperature->setValue(pcConstraint->initialTemperature.getQuantityValue());
+
+    ui->if_temperature->bind(pcConstraint->initialTemperature);
 }
 
 TaskFemConstraintInitialTemperature::~TaskFemConstraintInitialTemperature()
 {}
 
-double TaskFemConstraintInitialTemperature::get_temperature() const
+std::string TaskFemConstraintInitialTemperature::get_temperature() const
 {
-    Base::Quantity temperature = ui->if_temperature->getQuantity();
-    double temperature_in_kelvin = temperature.getValueAs(Base::Quantity::Kelvin);
-    return temperature_in_kelvin;
+    return ui->if_temperature->value().getSafeUserString().toStdString();
 }
 
 void TaskFemConstraintInitialTemperature::changeEvent(QEvent*)
@@ -119,9 +115,9 @@ bool TaskDlgFemConstraintInitialTemperature::accept()
 
     try {
         Gui::Command::doCommand(Gui::Command::Doc,
-                                "App.ActiveDocument.%s.initialTemperature = %f",
+                                "App.ActiveDocument.%s.initialTemperature = \"%s\"",
                                 name.c_str(),
-                                parameterTemperature->get_temperature());
+                                parameterTemperature->get_temperature().c_str());
 
         std::string scale = parameterTemperature->getScale();// OvG: determine modified scale
         Gui::Command::doCommand(Gui::Command::Doc,
diff --git a/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.h b/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.h
index f9200093cc..459ab7d718 100644
--- a/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.h
+++ b/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.h
@@ -44,7 +44,7 @@ public:
     explicit TaskFemConstraintInitialTemperature(
         ViewProviderFemConstraintInitialTemperature* ConstraintView, QWidget* parent = nullptr);
     ~TaskFemConstraintInitialTemperature() override;
-    double get_temperature()const;
+    std::string get_temperature() const;
 
 protected:
     void changeEvent(QEvent *e) override;
diff --git a/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.ui b/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.ui
index d304282de2..d4af9edc9e 100644
--- a/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.ui
+++ b/src/Mod/Fem/Gui/TaskFemConstraintInitialTemperature.ui
@@ -6,7 +6,7 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>300</width>
+    <width>268</width>
     <height>57</height>
    </rect>
   </property>
@@ -25,15 +25,12 @@
     </widget>
    </item>
    <item>
-    <widget class="Gui::InputField" name="if_temperature">
-     <property name="text">
-      <string>300 K</string>
-     </property>
+    <widget class="Gui::QuantitySpinBox" name="if_temperature">
      <property name="unit" stdset="0">
       <string notr="true">K</string>
      </property>
-     <property name="quantity" stdset="0">
-      <double>300.000000000000000</double>
+     <property name="minimum">
+      <double>0.000000000000000</double>
      </property>
     </widget>
    </item>
@@ -41,9 +38,9 @@
  </widget>
  <customwidgets>
   <customwidget>
-   <class>Gui::InputField</class>
-   <extends>QLineEdit</extends>
-   <header>Gui/InputField.h</header>
+   <class>Gui::QuantitySpinBox</class>
+   <extends>QWidget</extends>
+   <header>Gui/QuantitySpinBox.h</header>
   </customwidget>
  </customwidgets>
  <resources/>
diff --git a/src/Mod/Fem/Gui/TaskFemConstraintTemperature.cpp b/src/Mod/Fem/Gui/TaskFemConstraintTemperature.cpp
index 258f0b5c6b..e0da7de7fd 100644
--- a/src/Mod/Fem/Gui/TaskFemConstraintTemperature.cpp
+++ b/src/Mod/Fem/Gui/TaskFemConstraintTemperature.cpp
@@ -33,6 +33,7 @@
 
 #include <App/Document.h>
 #include <Gui/Command.h>
+#include <Gui/QuantitySpinBox.h>
 #include <Gui/SelectionObject.h>
 #include <Mod/Fem/App/FemConstraintTemperature.h>
 
@@ -54,23 +55,6 @@ TaskFemConstraintTemperature::TaskFemConstraintTemperature(
     ui->setupUi(proxy);
     QMetaObject::connectSlotsByName(this);
 
-    // create a context menu for the listview of the references
-    createDeleteAction(ui->lw_references);
-    connect(deleteAction, &QAction::triggered,
-            this, &TaskFemConstraintTemperature::onReferenceDeleted);
-
-    connect(ui->lw_references, &QListWidget::currentItemChanged,
-            this, &TaskFemConstraintTemperature::setSelection);
-    connect(ui->lw_references, &QListWidget::itemClicked,
-            this, &TaskFemConstraintTemperature::setSelection);
-    connect(ui->rb_temperature, &QRadioButton::clicked,
-            this, &TaskFemConstraintTemperature::Temp);
-    connect(ui->rb_cflux, &QRadioButton::clicked,
-            this, &TaskFemConstraintTemperature::Flux);
-
-    connect(ui->if_temperature, qOverload<double>(&InputField::valueChanged),
-            this, &TaskFemConstraintTemperature::onTempCfluxChanged);
-
     this->groupLayout()->addWidget(proxy);
 
     // Get the feature data
@@ -87,20 +71,17 @@ TaskFemConstraintTemperature::TaskFemConstraintTemperature(
     std::string constraint_type = pcConstraint->ConstraintType.getValueAsString();
     if (constraint_type == "Temperature") {
         ui->rb_temperature->setChecked(1);
-        std::string str = "Temperature";
-        QString qstr = QString::fromStdString(str);
-        ui->lbl_type->setText(qstr);
-        Base::Quantity t =
-            Base::Quantity(pcConstraint->Temperature.getValue(), Base::Unit::Temperature);
-        ui->if_temperature->setValue(t);
+        ui->if_temperature->setValue(pcConstraint->Temperature.getQuantityValue());
+
+        ui->if_temperature->bind(pcConstraint->Temperature);
+        ui->if_temperature->setUnit(pcConstraint->Temperature.getUnit());
     }
     else if (constraint_type == "CFlux") {
         ui->rb_cflux->setChecked(1);
         std::string str = "Concentrated heat flux";
-        QString qstr = QString::fromStdString(str);
-        ui->lbl_type->setText(qstr);
-        Base::Quantity c = Base::Quantity(pcConstraint->CFlux.getValue(), Base::Unit::Power);
-        ui->if_temperature->setValue(c);
+        ui->if_temperature->setValue(pcConstraint->CFlux.getQuantityValue());
+        ui->if_temperature->bind(pcConstraint->CFlux);
+        ui->if_temperature->setUnit(pcConstraint->CFlux.getUnit());
     }
 
     ui->lw_references->clear();
@@ -111,7 +92,28 @@ TaskFemConstraintTemperature::TaskFemConstraintTemperature(
         ui->lw_references->setCurrentRow(0, QItemSelectionModel::ClearAndSelect);
     }
 
-    //Selection buttons
+    // create a context menu for the listview of the references
+    createDeleteAction(ui->lw_references);
+    connect(
+        deleteAction, &QAction::triggered, this, &TaskFemConstraintTemperature::onReferenceDeleted);
+
+    connect(ui->lw_references,
+            &QListWidget::currentItemChanged,
+            this,
+            &TaskFemConstraintTemperature::setSelection);
+    connect(ui->lw_references,
+            &QListWidget::itemClicked,
+            this,
+            &TaskFemConstraintTemperature::setSelection);
+    connect(ui->rb_temperature, &QRadioButton::clicked, this, &TaskFemConstraintTemperature::Temp);
+    connect(ui->rb_cflux, &QRadioButton::clicked, this, &TaskFemConstraintTemperature::Flux);
+
+    connect(ui->if_temperature,
+            qOverload<double>(&QuantitySpinBox::valueChanged),
+            this,
+            &TaskFemConstraintTemperature::onTempCfluxChanged);
+
+    // Selection buttons
     buttonGroup->addButton(ui->btnAdd, (int)SelectionChangeModes::refAdd);
     buttonGroup->addButton(ui->btnRemove, (int)SelectionChangeModes::refRemove);
 
@@ -132,48 +134,22 @@ void TaskFemConstraintTemperature::updateUI()
 
 void TaskFemConstraintTemperature::onTempCfluxChanged(double val)
 {
-    Fem::ConstraintTemperature* pcConstraint =
-        static_cast<Fem::ConstraintTemperature*>(ConstraintView->getObject());
-    if (ui->rb_temperature->isChecked()) {
-        pcConstraint->Temperature.setValue(val);
-    }
-    else {
-        pcConstraint->CFlux.setValue(val);
-    }
 }
 
 void TaskFemConstraintTemperature::Temp()
 {
     Fem::ConstraintTemperature* pcConstraint =
         static_cast<Fem::ConstraintTemperature*>(ConstraintView->getObject());
-    std::string name = ConstraintView->getObject()->getNameInDocument();
-    Gui::Command::doCommand(Gui::Command::Doc,
-                            "App.ActiveDocument.%s.ConstraintType = %s",
-                            name.c_str(),
-                            get_constraint_type().c_str());
-    std::string str = "Temperature";
-    QString qstr = QString::fromStdString(str);
-    ui->lbl_type->setText(qstr);
-    Base::Quantity t = Base::Quantity(300, Base::Unit::Temperature);
-    ui->if_temperature->setValue(t);
-    pcConstraint->Temperature.setValue(300);
+    ui->if_temperature->setUnit(pcConstraint->Temperature.getUnit());
+    ui->if_temperature->setValue(pcConstraint->Temperature.getQuantityValue());
 }
 
 void TaskFemConstraintTemperature::Flux()
 {
     Fem::ConstraintTemperature* pcConstraint =
         static_cast<Fem::ConstraintTemperature*>(ConstraintView->getObject());
-    std::string name = ConstraintView->getObject()->getNameInDocument();
-    Gui::Command::doCommand(Gui::Command::Doc,
-                            "App.ActiveDocument.%s.ConstraintType = %s",
-                            name.c_str(),
-                            get_constraint_type().c_str());
-    std::string str = "Concentrated heat flux";
-    QString qstr = QString::fromStdString(str);
-    ui->lbl_type->setText(qstr);
-    Base::Quantity c = Base::Quantity(0, Base::Unit::Power);
-    ui->if_temperature->setValue(c);
-    pcConstraint->CFlux.setValue(0);
+    ui->if_temperature->setUnit(pcConstraint->CFlux.getUnit());
+    ui->if_temperature->setValue(pcConstraint->CFlux.getQuantityValue());
 }
 
 void TaskFemConstraintTemperature::addToSelection()
@@ -302,20 +278,21 @@ const std::string TaskFemConstraintTemperature::getReferences() const
     return TaskFemConstraint::getReferences(items);
 }
 
-double TaskFemConstraintTemperature::get_temperature() const {
-    Base::Quantity temperature = ui->if_temperature->getQuantity();
-    double temperature_in_kelvin = temperature.getValueAs(Base::Quantity::Kelvin);
-    return temperature_in_kelvin;
+std::string TaskFemConstraintTemperature::get_temperature() const
+{
+    return ui->if_temperature->value().getSafeUserString().toStdString();
 }
 
-double TaskFemConstraintTemperature::get_cflux() const {
-    Base::Quantity cflux = ui->if_temperature->getQuantity();
-    double cflux_in_watt = cflux.getValueAs(Base::Quantity::Watt);
-    return cflux_in_watt;
+std::string TaskFemConstraintTemperature::get_cflux() const
+{
+    return ui->if_temperature->value().getSafeUserString().toStdString();
 }
 
 std::string TaskFemConstraintTemperature::get_constraint_type() const {
+    Fem::ConstraintTemperature* pcConstraint =
+        static_cast<Fem::ConstraintTemperature*>(ConstraintView->getObject());
     std::string type;
+
     if (ui->rb_temperature->isChecked()) {
         type = "\"Temperature\"";
     }
@@ -385,7 +362,23 @@ bool TaskDlgFemConstraintTemperature::accept()
     const TaskFemConstraintTemperature* parameterTemperature =
         static_cast<const TaskFemConstraintTemperature*>(parameter);
 
+    auto type = parameterTemperature->get_constraint_type();
+
     try {
+        Gui::Command::doCommand(Gui::Command::Doc,
+                                    "App.ActiveDocument.%s.ConstraintType = %s",
+                                    name.c_str(),
+                                    parameterTemperature->get_constraint_type().c_str());
+        if (type == "Temperature")
+            Gui::Command::doCommand(Gui::Command::Doc,
+                                    "App.ActiveDocument.%s.Temperature = \"%s\"",
+                                    name.c_str(),
+                                    parameterTemperature->get_temperature().c_str());
+        else if (type == "CFlux")
+            Gui::Command::doCommand(Gui::Command::Doc,
+                                    "App.ActiveDocument.%s.CFlux = \"%s\"",
+                                    name.c_str(),
+                                    parameterTemperature->get_cflux().c_str());
         std::string scale = parameterTemperature->getScale();// OvG: determine modified scale
         Gui::Command::doCommand(Gui::Command::Doc,
                                 "App.ActiveDocument.%s.Scale = %s",
diff --git a/src/Mod/Fem/Gui/TaskFemConstraintTemperature.h b/src/Mod/Fem/Gui/TaskFemConstraintTemperature.h
index 291d35c6e7..d35d068f06 100644
--- a/src/Mod/Fem/Gui/TaskFemConstraintTemperature.h
+++ b/src/Mod/Fem/Gui/TaskFemConstraintTemperature.h
@@ -47,8 +47,8 @@ public:
     explicit TaskFemConstraintTemperature(ViewProviderFemConstraintTemperature *ConstraintView,QWidget *parent = nullptr);
     ~TaskFemConstraintTemperature() override;
     const std::string getReferences() const override;
-    double get_temperature()const;
-    double get_cflux() const;
+    std::string get_temperature() const;
+    std::string get_cflux() const;
     std::string get_constraint_type() const;
 
 private Q_SLOTS:
diff --git a/src/Mod/Fem/Gui/TaskFemConstraintTemperature.ui b/src/Mod/Fem/Gui/TaskFemConstraintTemperature.ui
index aad6ac3dc4..515afe6084 100644
--- a/src/Mod/Fem/Gui/TaskFemConstraintTemperature.ui
+++ b/src/Mod/Fem/Gui/TaskFemConstraintTemperature.ui
@@ -82,15 +82,12 @@
       </widget>
      </item>
      <item>
-      <widget class="Gui::InputField" name="if_temperature">
-       <property name="text">
-        <string>300 K</string>
-       </property>
+      <widget class="Gui::QuantitySpinBox" name="if_temperature">
        <property name="unit" stdset="0">
         <string notr="true">K</string>
        </property>
-       <property name="quantity" stdset="0">
-        <double>300.000000000000000</double>
+       <property name="minimum">
+        <double>0.000000000000000</double>
        </property>
       </widget>
      </item>
@@ -100,9 +97,9 @@
  </widget>
  <customwidgets>
   <customwidget>
-   <class>Gui::InputField</class>
-   <extends>QLineEdit</extends>
-   <header>Gui/InputField.h</header>
+   <class>Gui::QuantitySpinBox</class>
+   <extends>QWidget</extends>
+   <header>Gui/QuantitySpinBox.h</header>
   </customwidget>
  </customwidgets>
  <resources/>
diff --git a/src/Mod/Fem/femsolver/calculix/write_constraint_initialtemperature.py b/src/Mod/Fem/femsolver/calculix/write_constraint_initialtemperature.py
index 7db9523ffa..36b024dbdd 100644
--- a/src/Mod/Fem/femsolver/calculix/write_constraint_initialtemperature.py
+++ b/src/Mod/Fem/femsolver/calculix/write_constraint_initialtemperature.py
@@ -25,6 +25,8 @@ __title__ = "FreeCAD FEM calculix constraint initialtemperature"
 __author__ = "Bernd Hahnebach"
 __url__ = "https://www.freecadweb.org"
 
+import FreeCAD
+
 
 def get_analysis_types():
     return ["thermomech"]
@@ -46,7 +48,12 @@ def write_constraint(f, femobj, inittemp_obj, ccxwriter):
 
     # floats read from ccx should use {:.13G}, see comment in writer module
 
-    f.write("{},{:.13G}\n".format(ccxwriter.ccx_nall, inittemp_obj.initialTemperature))
+    f.write(
+            "{},{}\n".format(
+                ccxwriter.ccx_nall,
+                FreeCAD.Units.Quantity(inittemp_obj.initialTemperature.getValueAs("K"))
+            )
+        )
 
 
 # Should only be one object in the analysis
diff --git a/src/Mod/Fem/femsolver/calculix/write_constraint_temperature.py b/src/Mod/Fem/femsolver/calculix/write_constraint_temperature.py
index a8e534ddee..8b5879ae9b 100644
--- a/src/Mod/Fem/femsolver/calculix/write_constraint_temperature.py
+++ b/src/Mod/Fem/femsolver/calculix/write_constraint_temperature.py
@@ -25,6 +25,8 @@ __title__ = "FreeCAD FEM calculix constraint temperature"
 __author__ = "Bernd Hahnebach"
 __url__ = "https://www.freecadweb.org"
 
+import FreeCAD
+
 
 def get_analysis_types():
     return ["thermomech"]
@@ -68,12 +70,19 @@ def write_constraint(f, femobj, temp_obj, ccxwriter):
     NumberOfNodes = len(femobj["Nodes"])
     if temp_obj.ConstraintType == "Temperature":
         f.write("*BOUNDARY\n")
-        f.write("{},11,11,{:.13G}\n".format(temp_obj.Name, temp_obj.Temperature))
+        f.write(
+            "{},11,11,{}\n".format(
+                temp_obj.Name, FreeCAD.Units.Quantity(temp_obj.Temperature.getValueAs("K"))
+            )
+        )
         f.write("\n")
     elif temp_obj.ConstraintType == "CFlux":
         f.write("*CFLUX\n")
-        f.write("{},11,{:.13G}\n".format(
-            temp_obj.Name,
-            temp_obj.CFlux * 0.001 / NumberOfNodes
-        ))
+        # CFLUX has to be specified in mW
+        f.write(
+            "{},11,{}\n".format(
+                temp_obj.Name,
+                FreeCAD.Units.Quantity(temp_obj.CFlux.getValueAs("mW")) / NumberOfNodes
+            )
+        )
         f.write("\n")
diff --git a/src/Mod/Fem/femsolver/elmer/equations/deformation_writer.py b/src/Mod/Fem/femsolver/elmer/equations/deformation_writer.py
index 39191256b9..a473e0779d 100644
--- a/src/Mod/Fem/femsolver/elmer/equations/deformation_writer.py
+++ b/src/Mod/Fem/femsolver/elmer/equations/deformation_writer.py
@@ -186,7 +186,7 @@ class DeformationWriter:
         # temperature
         tempObj = self.write.getSingleMember("Fem::ConstraintInitialTemperature")
         if tempObj is not None:
-            refTemp = self.write.getFromUi(tempObj.initialTemperature, "K", "O")
+            refTemp = float(tempObj.initialTemperature.getValueAs("K"))
             for name in bodies:
                 self.write.material(name, "Reference Temperature", refTemp)
         # get the material data for all bodies
diff --git a/src/Mod/Fem/femsolver/elmer/equations/elasticity_writer.py b/src/Mod/Fem/femsolver/elmer/equations/elasticity_writer.py
index 70c2de265f..975c1f2689 100644
--- a/src/Mod/Fem/femsolver/elmer/equations/elasticity_writer.py
+++ b/src/Mod/Fem/femsolver/elmer/equations/elasticity_writer.py
@@ -402,7 +402,7 @@ class ElasticityWriter:
         # temperature
         tempObj = self.write.getSingleMember("Fem::ConstraintInitialTemperature")
         if tempObj is not None:
-            refTemp = self.write.getFromUi(tempObj.initialTemperature, "K", "O")
+            refTemp = float(tempObj.initialTemperature.getValueAs("K"))
             for name in bodies:
                 self.write.material(name, "Reference Temperature", refTemp)
         # get the material data for all bodies
diff --git a/src/Mod/Fem/femsolver/elmer/equations/flow_writer.py b/src/Mod/Fem/femsolver/elmer/equations/flow_writer.py
index 176706a56d..59c2e925ab 100644
--- a/src/Mod/Fem/femsolver/elmer/equations/flow_writer.py
+++ b/src/Mod/Fem/femsolver/elmer/equations/flow_writer.py
@@ -126,7 +126,7 @@ class Flowwriter:
     def handleFlowMaterial(self, bodies):
         tempObj = self.write.getSingleMember("Fem::ConstraintInitialTemperature")
         if tempObj is not None:
-            refTemp = self.write.getFromUi(tempObj.initialTemperature, "K", "O")
+            refTemp = float(tempObj.initialTemperature.getValueAs("K"))
             for name in bodies:
                 self.write.material(name, "Reference Temperature", refTemp)
         for obj in self.write.getMember("App::MaterialObject"):
diff --git a/src/Mod/Fem/femsolver/elmer/equations/heat_writer.py b/src/Mod/Fem/femsolver/elmer/equations/heat_writer.py
index ac42e6841f..d5f4dc9334 100644
--- a/src/Mod/Fem/femsolver/elmer/equations/heat_writer.py
+++ b/src/Mod/Fem/femsolver/elmer/equations/heat_writer.py
@@ -103,12 +103,10 @@ class Heatwriter:
             if obj.References:
                 for name in obj.References[0][1]:
                     if obj.ConstraintType == "Temperature":
-                        temp = self.write.getFromUi(obj.Temperature, "K", "O")
-                        self.write.boundary(name, "Temperature", temp)
+                        temperature = float(obj.Temperature.getValueAs("K"))
+                        self.write.boundary(name, "Temperature", temperature)
                     elif obj.ConstraintType == "CFlux":
-                        # the CFLUX property stores the value in µW
-                        # but the unit system is not aware of µW, only of mW
-                        flux = 0.001 * self.write.getFromUi(obj.CFlux, "mW", "M*L^2*T^-3")
+                        flux = float(obj.CFlux.getValueAs("W"))
                         # CFLUX is the flux per mesh node
                         flux = flux / NumberOfNodes
                         self.write.boundary(name, "Temperature Load", flux)
@@ -128,12 +126,12 @@ class Heatwriter:
                 self.write.handled(obj)
 
     def handleHeatInitial(self, bodies):
-        obj = self.write.getSingleMember("Fem::ConstraintInitialTemperature")
-        if obj is not None:
-            for name in bodies:
-                temp = self.write.getFromUi(obj.initialTemperature, "K", "O")
-                self.write.initial(name, "Temperature", temp)
-            self.write.handled(obj)
+        tempObj = self.write.getSingleMember("Fem::ConstraintInitialTemperature")
+        if tempObj is not None:
+            refTemp = float(tempObj.initialTemperature.getValueAs("K"))
+            for name in bodies:              
+                self.write.initial(name, "Temperature", refTemp)
+            self.write.handled(tempObj)
 
     def _outputHeatBodyForce(self, obj, name):
         heatSource = self.write.getFromUi(obj.HeatSource, "W/kg", "L^2*T^-3")
@@ -165,7 +163,7 @@ class Heatwriter:
     def handleHeatMaterial(self, bodies):
         tempObj = self.write.getSingleMember("Fem::ConstraintInitialTemperature")
         if tempObj is not None:
-            refTemp = self.write.getFromUi(tempObj.initialTemperature, "K", "O")
+            refTemp = float(tempObj.initialTemperature.getValueAs("K"))
             for name in bodies:
                 self.write.material(name, "Reference Temperature", refTemp)
         for obj in self.write.getMember("App::MaterialObject"):
diff --git a/src/Mod/Fem/femtest/data/calculix/thermomech_bimetall.inp b/src/Mod/Fem/femtest/data/calculix/thermomech_bimetall.inp
index 2217e283e6..2be2695488 100644
--- a/src/Mod/Fem/femtest/data/calculix/thermomech_bimetall.inp
+++ b/src/Mod/Fem/femtest/data/calculix/thermomech_bimetall.inp
@@ -7070,7 +7070,7 @@ Evolumes
 ** Initial temperature constraint
 *INITIAL CONDITIONS,TYPE=TEMPERATURE
 ** ConstraintInitialTemperature
-Nall,273
+Nall,273.0
 
 ***********************************************************
 ** Sections
@@ -7096,11 +7096,11 @@ ConstraintFixed,3
 ** Fixed temperature constraint applied
 ** ConstraintTemperatureHot
 *BOUNDARY
-ConstraintTemperatureHot,11,11,373
+ConstraintTemperatureHot,11,11,373.0
 
 ** ConstraintTemperatureNormal
 *BOUNDARY
-ConstraintTemperatureNormal,11,11,273
+ConstraintTemperatureNormal,11,11,273.0
 
 
 ***********************************************************
diff --git a/src/Mod/Fem/femtest/data/calculix/thermomech_spine.inp b/src/Mod/Fem/femtest/data/calculix/thermomech_spine.inp
index 7cc0b503a3..92a36026b0 100644
--- a/src/Mod/Fem/femtest/data/calculix/thermomech_spine.inp
+++ b/src/Mod/Fem/femtest/data/calculix/thermomech_spine.inp
@@ -123,7 +123,7 @@ Evolumes
 ** Initial temperature constraint
 *INITIAL CONDITIONS,TYPE=TEMPERATURE
 ** FemConstraintInitialTemperature
-Nall,300
+Nall,300.0
 
 ***********************************************************
 ** Sections