diff --git a/half-earth/scripts/HeatSystem.cs b/half-earth/scripts/HeatSystem.cs
new file mode 100644
index 0000000..ebeb79d
--- /dev/null
+++ b/half-earth/scripts/HeatSystem.cs
@@ -0,0 +1,100 @@
+using Godot;
+
+public class HeatSystem
+{
+    private readonly TileGrid _tiles;
+    private readonly float _diffusionCoefficient;
+
+    private float[] _nextTemperatures = null;
+
+    public HeatSystem(TileGrid tiles, float diffusionCoefficient)
+    {
+        _tiles = tiles;
+        _diffusionCoefficient = diffusionCoefficient;
+        _nextTemperatures = new float[tiles.Count];
+    }
+
+    public void Process()
+    {
+        GenerateHeat();
+        Diffuse();
+    }
+
+
+    private float TransferHeat(float t0, float alpha, float nx, float ny, float px, float py)
+    {
+        float d2tdx2 = nx - 2 * t0 + px;
+        float d2tdy2 = ny - 2 * t0 + py;
+        return t0 + alpha * (d2tdx2 + d2tdy2);
+    }
+
+    private void GetNeighbourTemperatures(int x, int y, out float nx, out float ny, out float px, out float py)
+    {
+        // default value
+        var t = _tiles[x, y].temperature;
+
+        nx = x > 0 ? _tiles[x - 1, y].temperature : t;
+        px = x < _tiles.Size - 1 ? _tiles[x + 1, y].temperature : t;
+
+        ny = y > 0 ? _tiles[x, y - 1].temperature : t;
+        py = y < _tiles.Size - 1 ? _tiles[x, y + 1].temperature : t;
+    }
+    private void GenerateHeat()
+    {
+        for (int i = 0; i < _tiles.Count; i++)
+        {
+            var tile = _tiles[i];
+            var type = tile.type;
+            tile.temperature += type.HeatGeneration;
+            ApplyHeatDamage(ref tile);
+            _tiles[i] = tile;
+        }
+    }
+
+    private void ApplyHeatDamage(ref Tile tile)
+    {
+        if (!(tile.type is IDamageable damageable))
+            return;
+
+        var surplus = tile.temperature - damageable.Threshold;
+        if (surplus < 0)
+            return;
+
+        // TODO: parameterised balancing
+        tile.currentHealth -= surplus;
+        tile.currentHealth = Mathf.Clamp(tile.currentHealth, 0, 1);
+    }
+
+    private void Diffuse()
+    {
+        var D = _diffusionCoefficient;
+
+        for (int i = 0; i < _tiles.Count; i++)
+        {
+            float t = _tiles[i].temperature;
+
+            _tiles.MapIndex(i, out var x, out var y);
+
+            GetNeighbourTemperatures(
+                x, y,
+                out var nx,
+                out var ny,
+                out var px,
+                out var py);
+
+            var temperature = TransferHeat(t, D, nx, ny, px, py);
+
+            // TODO: what if it's really really cold out?
+            temperature = Mathf.Max(0, temperature);
+            _nextTemperatures[i] = temperature;
+        }
+
+        for (int i = 0; i < _tiles.Count; i++)
+        {
+            var tile = _tiles[i];
+            tile.temperature = _nextTemperatures[i];
+            _tiles[i] = tile;
+        }
+    }
+
+}
diff --git a/half-earth/scripts/WorldGrid.cs b/half-earth/scripts/WorldGrid.cs
index 83c546e..fb78f04 100644
--- a/half-earth/scripts/WorldGrid.cs
+++ b/half-earth/scripts/WorldGrid.cs
@@ -16,13 +16,12 @@ public class WorldGrid : Node2D
     [Export]
     public float DiffusionCoefficient { get; set; } = 0.01f;
 
-    private float[] _nextValues = null;
-
     public struct TileView
     {
         public ShaderMaterial material;
     }
     private TileView[] _tileViews;
+    private HeatSystem _heat;
 
     // Called when the node enters the scene tree for the first time.
     public override void _Ready()
@@ -30,6 +29,8 @@ public class WorldGrid : Node2D
         _tileGrid = (TileGrid)_tileGridResource;
 
         GenerateCanvasItems(_tileGrid);
+
+        _heat = new HeatSystem(_tileGrid, DiffusionCoefficient);
     }
 
     #region Positioning
@@ -53,8 +54,6 @@ public class WorldGrid : Node2D
         var tile = _tileGrid[idx];
         tile.type = tileType;
         _tileGrid[x, y] = tile;
-
-        _tileViews[idx].material.SetShaderParam("lowColor", tileType.Color);
     }
     #endregion
 
@@ -76,7 +75,6 @@ public class WorldGrid : Node2D
         this.Clear();
 
         _tileViews = new TileView[grid.Count];
-        _nextValues = new float[grid.Count];
 
         for (int i = 0; i < grid.Count; i++)
         {
@@ -96,95 +94,11 @@ public class WorldGrid : Node2D
 
             TileView view = default;
             view.material = (ShaderMaterial)canvasItem.Material;
-            //view.material.SetShaderParam("lowColor", _tileGrid.StartTileType.Color);
             _tileViews[i] = view;
         }
     }
 
     public ShaderMaterial GetTileMaterial(int idx) => _tileViews[idx].material;
 
-    #region Simulation
-    public void _on_Clock_OnTick(int ticks)
-    {
-        GenerateHeat();
-        Diffuse();
-    }
-
-    private float TransferHeat(float t0, float alpha, float nx, float ny, float px, float py)
-    {
-        float d2tdx2 = nx - 2 * t0 + px;
-        float d2tdy2 = ny - 2 * t0 + py;
-        return t0 + alpha * (d2tdx2 + d2tdy2);
-    }
-
-    private void GetNeighbourTemperatures(int x, int y, out float nx, out float ny, out float px, out float py)
-    {
-        // default value
-        var t = _tileGrid[x, y].temperature;
-
-        nx = x > 0 ? _tileGrid[x - 1, y].temperature : t;
-        px = x < _tileGrid.Size - 1 ? _tileGrid[x + 1, y].temperature : t;
-
-        ny = y > 0 ? _tileGrid[x, y - 1].temperature : t;
-        py = y < _tileGrid.Size - 1 ? _tileGrid[x, y + 1].temperature : t;
-    }
-
-    private void ApplyHeatDamage(ref Tile tile)
-    {
-        if (!(tile.type is IDamageable damageable))
-            return;
-
-        var surplus = tile.temperature - damageable.Threshold;
-        if (surplus < 0)
-            return;
-
-        // TODO: parameterised balancing
-        tile.currentHealth -= surplus;
-        tile.currentHealth = Mathf.Clamp(tile.currentHealth, 0, 1);
-    }
-
-    private void GenerateHeat()
-    {
-        for (int i = 0; i < _tileGrid.Count; i++)
-        {
-            var tile = _tileGrid[i];
-            var type = tile.type;
-            tile.temperature += type.HeatGeneration;
-            ApplyHeatDamage(ref tile);
-            _tileGrid[i] = tile;
-        }
-    }
-
-    private void Diffuse()
-    {
-        var D = DiffusionCoefficient;
-
-        for (int i = 0; i < _tileGrid.Count; i++)
-        {
-            float t = _tileGrid[i].temperature;
-
-            _tileGrid.MapIndex(i, out var x, out var y);
-
-            GetNeighbourTemperatures(
-                x, y,
-                out var nx,
-                out var ny,
-                out var px,
-                out var py);
-
-            var temperature = TransferHeat(t, D, nx, ny, px, py);
-
-            // TODO: what if it's really really cold out?
-            temperature = Mathf.Max(0, temperature);
-            _nextValues[i] = temperature;
-        }
-
-        for (int i = 0; i < _tileGrid.Count; i++)
-        {
-            var tile = _tileGrid[i];
-            tile.temperature = _nextValues[i];
-            _tileGrid[i] = tile;
-        }
-    }
-    #endregion
+    public void _on_Clock_OnTick(int ticks) => _heat.Process();
 }