diff --git a/MatterControl.Printing/GCode/GCodeFile.cs b/MatterControl.Printing/GCode/GCodeFile.cs
index 48357be04..330a64979 100644
--- a/MatterControl.Printing/GCode/GCodeFile.cs
+++ b/MatterControl.Printing/GCode/GCodeFile.cs
@@ -76,6 +76,13 @@ namespace MatterControl.Printing
 
 		public abstract double GetLayerHeight(int layerIndex);
 
+		/// <summary>
+		/// Get the speed of the fan at the conculsion of this layer
+		/// </summary>
+		/// <param name="layerIndex">The layer to get the last fan speed for</param>
+		/// <returns>The fan speed 0 to 255</returns>
+		public abstract int GetLastFanSpeed(int layerIndex);
+
 		public abstract double GetLayerTop(int layerIndex);
 
 		public abstract int GetLayerIndex(int instructionIndex);
diff --git a/MatterControl.Printing/GCode/GCodeFileStreamed.cs b/MatterControl.Printing/GCode/GCodeFileStreamed.cs
index 7e5fbd2dc..aab1b5075 100644
--- a/MatterControl.Printing/GCode/GCodeFileStreamed.cs
+++ b/MatterControl.Printing/GCode/GCodeFileStreamed.cs
@@ -164,7 +164,12 @@ namespace MatterControl.Printing
 			throw new NotImplementedException();
 		}
 
-		public override double PercentComplete(int instructionIndex)
+        public override int GetLastFanSpeed(int layerIndex)
+        {
+			return -1;
+        }
+
+        public override double PercentComplete(int instructionIndex)
 		{
 			lock(locker)
 			{
diff --git a/MatterControl.Printing/GCode/GCodeMemoryFile.cs b/MatterControl.Printing/GCode/GCodeMemoryFile.cs
index 85b33357f..b51dfacdf 100644
--- a/MatterControl.Printing/GCode/GCodeMemoryFile.cs
+++ b/MatterControl.Printing/GCode/GCodeMemoryFile.cs
@@ -51,6 +51,8 @@ namespace MatterControl.Printing
 		private double parsingLastZ;
 		private readonly List<int> toolChanges = new List<int>();
 
+		private Dictionary<int, int> lastFanSpeed = new Dictionary<int, int>();
+
 		/// <summary>
 		/// Gets total print time that will leave the heaters on at the conclusion of the print.
 		/// </summary>
@@ -290,6 +292,70 @@ namespace MatterControl.Printing
 			return total;
 		}
 
+		public override int GetLastFanSpeed(int requestedLayer)
+		{
+			if (LayerCount == 0 || requestedLayer < 0)
+			{
+				return 0;
+			}
+
+			if (lastFanSpeed.ContainsKey(requestedLayer))
+            {
+				return lastFanSpeed[requestedLayer];
+            }
+
+			var currentLayer = requestedLayer;
+			while (currentLayer >= 0)
+			{
+				int startInstruction = GetFirstLayerInstruction(currentLayer);
+				if (currentLayer == 0)
+				{
+					startInstruction = 0;
+				}
+
+				int endInstruction = GetFirstLayerInstruction(currentLayer + 1);
+
+				var foundSpeed = false;
+				var lastSpeed = 0;
+				for (int i = startInstruction; i < endInstruction; i++)
+				{
+					var line = Instruction(i).Line;
+					if (line.StartsWith("M107")) // fan off
+					{
+						foundSpeed = true;
+						lastSpeed = 0;
+					}
+					else if (line.StartsWith("M106")) // fan on
+					{
+						double speed = 0;
+						if (GCodeFile.GetFirstNumberAfter("S", line, ref speed, 0, ""))
+						{
+							foundSpeed = true;
+							lastSpeed = (int)speed;
+						}
+					}
+				}
+
+				if (foundSpeed)
+				{
+					lastFanSpeed[requestedLayer] = lastSpeed;
+					return lastSpeed;
+				}
+
+				currentLayer--;
+
+				if (lastFanSpeed.ContainsKey(currentLayer))
+				{
+					lastFanSpeed[currentLayer + 1] = lastFanSpeed[currentLayer];
+					lastFanSpeed[requestedLayer] = lastFanSpeed[currentLayer];
+					return lastFanSpeed[currentLayer];
+				}
+			}
+
+			lastFanSpeed[requestedLayer] = 0;
+			return 0;
+		}
+
 		/// <summary>
 		/// Get the height of this layer (from the top of the previous layer to the top of this layer).
 		/// </summary>
diff --git a/MatterControlLib/PartPreviewWindow/GCodeDetails/GCodeDetails.cs b/MatterControlLib/PartPreviewWindow/GCodeDetails/GCodeDetails.cs
index 320b415f5..7f9822a6e 100644
--- a/MatterControlLib/PartPreviewWindow/GCodeDetails/GCodeDetails.cs
+++ b/MatterControlLib/PartPreviewWindow/GCodeDetails/GCodeDetails.cs
@@ -27,7 +27,6 @@ of the authors and should not be interpreted as representing official policies,
 either expressed or implied, of the FreeBSD Project.
 */
 
-using System;
 using System.Collections.Generic;
 using MatterControl.Printing;
 using MatterHackers.MatterControl.SlicerConfiguration;
@@ -234,12 +233,38 @@ namespace MatterHackers.MatterControl.PartPreviewWindow
 					double speed = 0;
 					if (GCodeFile.GetFirstNumberAfter("S", line, ref speed, 0, ""))
 					{
-						fanSpeeds += separator + $"{speed * 100 / 255:0}%";
+						if (speed == 0)
+						{
+							fanSpeeds += separator + "Off";
+						}
+						else
+						{
+							fanSpeeds += separator + $"{speed * 100 / 255:0}%";
+						}
 						separator = ", ";
 					}
 				}
 			}
 
+			if (string.IsNullOrEmpty(fanSpeeds))
+            {
+				// look back until we find a speed or go back to the begining
+				var speed = loadedGCode.GetLastFanSpeed(activeLayerIndex - 1);
+				if (speed >= 0)
+				{
+					if (speed == 0)
+                    {
+						return "Off";
+                    }
+
+					return $"{speed * 100 / 255:0}%";
+				}
+				else
+				{
+					return "---";
+				}
+			}
+
 			return fanSpeeds;
 		}