diff --git a/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.cpp b/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.cpp
index 25943179..5e6d7c6d 100644
--- a/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.cpp
+++ b/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.cpp
@@ -1,4 +1,4 @@
-#include "PoissonPIC.h"
+#include "PoissonPIC.hpp"
 
 using namespace std;
 
diff --git a/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.h b/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.h
deleted file mode 100644
index b709fe23..00000000
--- a/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.h
+++ /dev/null
@@ -1,56 +0,0 @@
-#ifndef NEKTAR_SOLVERS_EQUATIONSYSTEMS_POISSON_PIC_H
-#define NEKTAR_SOLVERS_EQUATIONSYSTEMS_POISSON_PIC_H
-
-#include <map>
-#include <string>
-
-#include <SolverUtils/EquationSystem.h>
-using namespace Nektar::SolverUtils;
-
-namespace Nektar
-{
-class PoissonPIC : public EquationSystem
-{
-public:
-    std::map<std::string, int> field_to_index;
-
-    friend class MemoryManager<PoissonPIC>;
-
-    /// Creates an instance of this class
-    static EquationSystemSharedPtr create(
-        const LibUtilities::SessionReaderSharedPtr &pSession,
-        const SpatialDomains::MeshGraphSharedPtr &pGraph)
-    {
-        EquationSystemSharedPtr p =
-            MemoryManager<PoissonPIC>::AllocateSharedPtr(pSession, pGraph);
-        p->InitObject();
-        return p;
-    }
-    /// Name of class
-    static std::string className1;
-    static std::string className2;
-
-    virtual ~PoissonPIC();
-    /**
-     *  Helper function to map from field name to field indices.
-     *
-     *  @param name Field name (probably either "u" or "rho").
-     *  @returns index (probably 0 or 1).
-     */
-    int GetFieldIndex(const std::string name);
-
-protected:
-    StdRegions::ConstFactorMap m_factors;
-    PoissonPIC(const LibUtilities::SessionReaderSharedPtr &pSession,
-            const SpatialDomains::MeshGraphSharedPtr &pGraph);
-
-    virtual void v_InitObject(bool DeclareFields = true);
-    virtual void v_DoSolve();
-    virtual void v_GenerateSummary(SolverUtils::SummaryList &s);
-
-private:
-    virtual Array<OneD, bool> v_GetSystemSingularChecks();
-};
-} // namespace Nektar
-
-#endif
diff --git a/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.hpp b/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.hpp
new file mode 100644
index 00000000..c7b5ce9a
--- /dev/null
+++ b/solvers/Electrostatic2D3V/EquationSystems/PoissonPIC.hpp
@@ -0,0 +1,53 @@
+#ifndef NEKTAR_SOLVERS_EQUATIONSYSTEMS_POISSON_PIC_H
+#define NEKTAR_SOLVERS_EQUATIONSYSTEMS_POISSON_PIC_H
+
+#include <map>
+#include <string>
+
+#include <SolverUtils/EquationSystem.h>
+using namespace Nektar::SolverUtils;
+
+namespace Nektar {
+class PoissonPIC : public EquationSystem {
+public:
+  std::map<std::string, int> field_to_index;
+
+  friend class MemoryManager<PoissonPIC>;
+
+  /// Creates an instance of this class
+  static EquationSystemSharedPtr
+  create(const LibUtilities::SessionReaderSharedPtr &pSession,
+         const SpatialDomains::MeshGraphSharedPtr &pGraph) {
+    EquationSystemSharedPtr p =
+        MemoryManager<PoissonPIC>::AllocateSharedPtr(pSession, pGraph);
+    p->InitObject();
+    return p;
+  }
+  /// Name of class
+  static std::string className1;
+  static std::string className2;
+
+  virtual ~PoissonPIC();
+  /**
+   *  Helper function to map from field name to field indices.
+   *
+   *  @param name Field name (probably either "u" or "rho").
+   *  @returns index (probably 0 or 1).
+   */
+  int GetFieldIndex(const std::string name);
+
+protected:
+  StdRegions::ConstFactorMap m_factors;
+  PoissonPIC(const LibUtilities::SessionReaderSharedPtr &pSession,
+             const SpatialDomains::MeshGraphSharedPtr &pGraph);
+
+  virtual void v_InitObject(bool DeclareFields = true);
+  virtual void v_DoSolve();
+  virtual void v_GenerateSummary(SolverUtils::SummaryList &s);
+
+private:
+  virtual Array<OneD, bool> v_GetSystemSingularChecks();
+};
+} // namespace Nektar
+
+#endif
diff --git a/solvers/Electrostatic2D3V/ParticleSystems/poisson_particle_coupling.hpp b/solvers/Electrostatic2D3V/ParticleSystems/poisson_particle_coupling.hpp
index 0c921933..fa395023 100644
--- a/solvers/Electrostatic2D3V/ParticleSystems/poisson_particle_coupling.hpp
+++ b/solvers/Electrostatic2D3V/ParticleSystems/poisson_particle_coupling.hpp
@@ -21,7 +21,7 @@
 #include <random>
 #include <string>
 
-#include "../EquationSystems/PoissonPIC.h"
+#include "../EquationSystems/PoissonPIC.hpp"
 #include "charged_particles.hpp"
 
 using namespace Nektar;
diff --git a/solvers/SimpleSOL/EquationSystems/SOLSystem.cpp b/solvers/SimpleSOL/EquationSystems/SOLSystem.cpp
index 5ca5cb37..bd153dbf 100644
--- a/solvers/SimpleSOL/EquationSystems/SOLSystem.cpp
+++ b/solvers/SimpleSOL/EquationSystems/SOLSystem.cpp
@@ -35,7 +35,7 @@
 #include <LibUtilities/TimeIntegration/TimeIntegrationScheme.h>
 #include <boost/core/ignore_unused.hpp>
 
-#include "SOLSystem.h"
+#include "SOLSystem.hpp"
 
 namespace Nektar {
 std::string SOLSystem::className =
diff --git a/solvers/SimpleSOL/EquationSystems/SOLSystem.h b/solvers/SimpleSOL/EquationSystems/SOLSystem.hpp
similarity index 99%
rename from solvers/SimpleSOL/EquationSystems/SOLSystem.h
rename to solvers/SimpleSOL/EquationSystems/SOLSystem.hpp
index 16fc3689..52399274 100644
--- a/solvers/SimpleSOL/EquationSystems/SOLSystem.h
+++ b/solvers/SimpleSOL/EquationSystems/SOLSystem.hpp
@@ -1,6 +1,6 @@
 ///////////////////////////////////////////////////////////////////////////////
 //
-// File SOLSystem.h
+// File SOLSystem.hpp
 //
 // For more information, please see: http://www.nektar.info
 //
diff --git a/solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.cpp b/solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.cpp
index 6d781bdb..c5068ae9 100644
--- a/solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.cpp
+++ b/solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.cpp
@@ -34,7 +34,7 @@
 
 #include <boost/algorithm/string/predicate.hpp>
 
-#include "SOLWithParticlesSystem.h"
+#include "SOLWithParticlesSystem.hpp"
 
 namespace Nektar {
 string SOLWithParticlesSystem::className =
diff --git a/solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.h b/solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.hpp
similarity index 98%
rename from solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.h
rename to solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.hpp
index df0fdc44..e5169091 100644
--- a/solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.h
+++ b/solvers/SimpleSOL/EquationSystems/SOLWithParticlesSystem.hpp
@@ -1,6 +1,6 @@
 ///////////////////////////////////////////////////////////////////////////////
 //
-// File SOLWithParticlesSystem.h
+// File SOLWithParticlesSystem.hpp
 //
 // For more information, please see: http://www.nektar.info
 //
@@ -37,9 +37,9 @@
 
 #include "../Diagnostics/mass_conservation.hpp"
 #include "../ParticleSystems/neutral_particles.hpp"
-#include "SOLSystem.h"
-#include <string>
+#include "SOLSystem.hpp"
 #include <solvers/solver_callback_handler.hpp>
+#include <string>
 
 namespace Nektar {
 /**
@@ -92,9 +92,7 @@ class SOLWithParticlesSystem : public SOLSystem,
    */
   std::shared_ptr<NeutralParticleSystem> GetNeutralParticleSystem();
 
-
 protected:
-
   // Flag to toggle mass conservation checking
   bool m_diag_mass_recording_enabled;
   // Map of field name to field index
diff --git a/solvers/SimpleSOL/Forcing/SourceTerms.cpp b/solvers/SimpleSOL/Forcing/SourceTerms.cpp
index 79497040..1f51f946 100644
--- a/solvers/SimpleSOL/Forcing/SourceTerms.cpp
+++ b/solvers/SimpleSOL/Forcing/SourceTerms.cpp
@@ -34,7 +34,7 @@
 
 #include <boost/core/ignore_unused.hpp>
 
-#include "SourceTerms.h"
+#include "SourceTerms.hpp"
 
 using namespace std;
 
diff --git a/solvers/SimpleSOL/Forcing/SourceTerms.h b/solvers/SimpleSOL/Forcing/SourceTerms.hpp
similarity index 99%
rename from solvers/SimpleSOL/Forcing/SourceTerms.h
rename to solvers/SimpleSOL/Forcing/SourceTerms.hpp
index de9363f9..dbaf5114 100644
--- a/solvers/SimpleSOL/Forcing/SourceTerms.h
+++ b/solvers/SimpleSOL/Forcing/SourceTerms.hpp
@@ -1,6 +1,6 @@
 ///////////////////////////////////////////////////////////////////////////////
 //
-// File: SourceTerms.h
+// File: SourceTerms.hpp
 //
 // For more information, please see: http://www.nektar.info
 //
diff --git a/solvers/SimpleSOL/SimpleSOL.cpp b/solvers/SimpleSOL/SimpleSOL.cpp
index 6c5c7b34..5b1624c5 100644
--- a/solvers/SimpleSOL/SimpleSOL.cpp
+++ b/solvers/SimpleSOL/SimpleSOL.cpp
@@ -10,7 +10,7 @@
 #include <LibUtilities/BasicUtils/SessionReader.h>
 #include <SolverUtils/Driver.h>
 
-#include "SimpleSOL.h"
+#include "SimpleSOL.hpp"
 
 using namespace Nektar;
 using namespace Nektar::SolverUtils;
diff --git a/solvers/SimpleSOL/SimpleSOL.h b/solvers/SimpleSOL/SimpleSOL.hpp
similarity index 87%
rename from solvers/SimpleSOL/SimpleSOL.h
rename to solvers/SimpleSOL/SimpleSOL.hpp
index 2867f804..028e3cfd 100644
--- a/solvers/SimpleSOL/SimpleSOL.h
+++ b/solvers/SimpleSOL/SimpleSOL.hpp
@@ -1,6 +1,6 @@
 ///////////////////////////////////////////////////////////////////////////////
 //
-// File: SimpleSOL.h
+// File: SimpleSOL.hpp
 //
 //
 // Description: Header for the SimpleSOL solver.
@@ -10,4 +10,4 @@ namespace NESO {
 namespace Solvers {
 int run_SimpleSOL(int argc, char *argv[]);
 }
-}
\ No newline at end of file
+} // namespace NESO
\ No newline at end of file
diff --git a/solvers/SimpleSOL/main.cpp b/solvers/SimpleSOL/main.cpp
index ec1b50a8..2bc3a5e5 100644
--- a/solvers/SimpleSOL/main.cpp
+++ b/solvers/SimpleSOL/main.cpp
@@ -6,7 +6,7 @@
 // Description: Entrypoint for the SimpleSOL solver.
 //
 ///////////////////////////////////////////////////////////////////////////////
-#include "SimpleSOL.h"
+#include "SimpleSOL.hpp"
 #include <iostream>
 #include <mpi.h>
 
diff --git a/test/integration/solvers/H3LAPD/test_H3LAPD.cpp b/test/integration/solvers/H3LAPD/test_H3LAPD.cpp
index e054740d..e7e3c0be 100644
--- a/test/integration/solvers/H3LAPD/test_H3LAPD.cpp
+++ b/test/integration/solvers/H3LAPD/test_H3LAPD.cpp
@@ -1,7 +1,7 @@
 #include <gtest/gtest.h>
 
 #include "H3LAPD.hpp"
-#include "test_H3LAPD.h"
+#include "test_H3LAPD.hpp"
 /**
  * Tests for the H3LAPD solver.
  */
@@ -12,4 +12,4 @@
  */
 TEST_F(HWTest, 2Din3DHWGrowthRates) { check_growth_rates(); }
 
-TEST_F(HWTest, Coupled2Din3DHWMassCons) { check_mass_cons(); }
\ No newline at end of file
+TEST_F(HWTest, Coupled2Din3DHWMassCons) { check_mass_cons(); }
diff --git a/test/integration/solvers/H3LAPD/test_H3LAPD.h b/test/integration/solvers/H3LAPD/test_H3LAPD.hpp
similarity index 99%
rename from test/integration/solvers/H3LAPD/test_H3LAPD.h
rename to test/integration/solvers/H3LAPD/test_H3LAPD.hpp
index 9f495373..ef2653c7 100644
--- a/test/integration/solvers/H3LAPD/test_H3LAPD.h
+++ b/test/integration/solvers/H3LAPD/test_H3LAPD.hpp
@@ -6,7 +6,7 @@
 #include "EquationSystems/DriftReducedSystem.hpp"
 #include "EquationSystems/HW2Din3DSystem.hpp"
 #include "H3LAPD.hpp"
-#include "solver_test_utils.h"
+#include "solver_test_utils.hpp"
 #include "solvers/solver_callback_handler.hpp"
 #include "solvers/solver_runner.hpp"
 
diff --git a/test/integration/solvers/SimpleSOL/test_SimpleSOL.cpp b/test/integration/solvers/SimpleSOL/test_SimpleSOL.cpp
index 722ef37b..14a8c0ae 100644
--- a/test/integration/solvers/SimpleSOL/test_SimpleSOL.cpp
+++ b/test/integration/solvers/SimpleSOL/test_SimpleSOL.cpp
@@ -1,7 +1,7 @@
 #include <gtest/gtest.h>
 
-#include "SimpleSOL.h"
-#include "test_SimpleSOL.h"
+#include "SimpleSOL.hpp"
+#include "test_SimpleSOL.hpp"
 
 /**
  * Tests for SimpleSOL solver. Note that the test name itself is used to
diff --git a/test/integration/solvers/SimpleSOL/test_SimpleSOL.h b/test/integration/solvers/SimpleSOL/test_SimpleSOL.hpp
similarity index 95%
rename from test/integration/solvers/SimpleSOL/test_SimpleSOL.h
rename to test/integration/solvers/SimpleSOL/test_SimpleSOL.hpp
index 6970ebe1..f8a423c5 100644
--- a/test/integration/solvers/SimpleSOL/test_SimpleSOL.h
+++ b/test/integration/solvers/SimpleSOL/test_SimpleSOL.hpp
@@ -4,19 +4,19 @@
 #include <boost/algorithm/string.hpp>
 #include <boost/program_options.hpp>
 #include <fstream>
-#include <vector>
 #include <gtest/gtest.h>
+#include <vector>
 
 #include <FieldUtils/Module.h>
 #include <LibUtilities/BasicConst/NektarUnivTypeDefs.hpp>
 #include <LibUtilities/BasicUtils/SharedArray.hpp>
 #include <LibUtilities/Communication/CommSerial.h>
 
-#include "SimpleSOL.h"
-#include "solver_test_utils.h"
-#include "solvers/solver_runner.hpp"
+#include "EquationSystems/SOLWithParticlesSystem.hpp"
+#include "SimpleSOL.hpp"
+#include "solver_test_utils.hpp"
 #include "solvers/solver_callback_handler.hpp"
-#include "EquationSystems/SOLWithParticlesSystem.h"
+#include "solvers/solver_runner.hpp"
 
 namespace LU = Nektar::LibUtilities;
 namespace FU = Nektar::FieldUtils;
@@ -186,14 +186,15 @@ class SimpleSOLTest : public NektarSolverTest {
   }
 };
 
-
-struct SOLWithParticlesMassConservationPre : public NESO::SolverCallback<SOLWithParticlesSystem> {
+struct SOLWithParticlesMassConservationPre
+    : public NESO::SolverCallback<SOLWithParticlesSystem> {
   void call(SOLWithParticlesSystem *state) {
     state->m_diag_mass_recording->compute_initial_fluid_mass();
   }
 };
 
-struct SOLWithParticlesMassConservationPost : public NESO::SolverCallback<SOLWithParticlesSystem> {
+struct SOLWithParticlesMassConservationPost
+    : public NESO::SolverCallback<SOLWithParticlesSystem> {
   std::vector<double> mass_error;
   void call(SOLWithParticlesSystem *state) {
     auto md = state->m_diag_mass_recording;
@@ -202,9 +203,9 @@ struct SOLWithParticlesMassConservationPost : public NESO::SolverCallback<SOLWit
     const double mass_total = mass_particles + mass_fluid;
     const double mass_added = md->compute_total_added_mass();
     const double correct_total = mass_added + md->get_initial_mass();
-    this->mass_error.push_back(std::fabs(correct_total - mass_total)/std::fabs(correct_total));
+    this->mass_error.push_back(std::fabs(correct_total - mass_total) /
+                               std::fabs(correct_total));
   }
 };
 
-
 #endif // SIMPLESOL_TESTS_COMMON
diff --git a/test/integration/solvers/solver_test_utils.cpp b/test/integration/solvers/solver_test_utils.cpp
index 54690658..0383a46d 100644
--- a/test/integration/solvers/solver_test_utils.cpp
+++ b/test/integration/solvers/solver_test_utils.cpp
@@ -1,4 +1,4 @@
-#include "solver_test_utils.h"
+#include "solver_test_utils.hpp"
 #include <mpi.h>
 
 // ============================= Helper functions =============================
diff --git a/test/integration/solvers/solver_test_utils.h b/test/integration/solvers/solver_test_utils.hpp
similarity index 100%
rename from test/integration/solvers/solver_test_utils.h
rename to test/integration/solvers/solver_test_utils.hpp