diff --git a/pool.js b/pool.js
index 62933f8..01b3759 100644
--- a/pool.js
+++ b/pool.js
@@ -28,27 +28,37 @@ let status = {
   tick_day: 0,
 };
 
-// compute duration of filtration for a given max temperature
+// temperature->duration chart
+let filt_time = [
+  [  5,  1.0 ],  // at 5°C, 1 hour of filtering
+  [ 10,  2.0 ],
+  [ 12,  4.0 ],
+  [ 16,  6.0 ],
+  [ 24,  8.0 ],
+  [ 27, 12.0 ],
+  [ 30, 24.0 ]
+];
+
+// compute filtration time for a given max temperature
 // duration is returned in float format (1.25 -> 1h 15mn)
 
-function compute_duration_filt(t) {
-  if (t < 5)
-    return 1;
-  if (t < 10)
-    return (t/5);           // 1 -> 2
-  if (t < 12)
-    return (t-8);           // 2 -> 4
-  if (t < 16)
-    return (t/2-2);         // 4 -> 6
-  if (t < 24)
-    return (t/4+2);         // 6 -> 8
-  if (t < 27)
-    return (t*4/3-24)       // 8 -> 12
-  if (t < 30)
-    return (t*4 - 96);      // 12 -> 24
-  return 24;
+function compute_filtration_time(t) {
+  let len = filt_time.length;
+
+  if (t < filt_time[0][0])
+    return filt_time[0][1];
+
+  for (let i = 0; i < len-1; i++) {
+    if (t >= filt_time[i][0] && t < filt_time[i+1][0]) {
+      // linear interpolation between two points
+      return filt_time[i][1] + (filt_time[i+1][1] - filt_time[i][1]) / (filt_time[i+1][0] - filt_time[i][0]) * (t - filt_time[i][0]);
+    }
+  }
+
+  return filt_time[len-1][1];
 }
 
+
 // compute the pump schedule for a given duration
 // returns an array of start/stop times in float
 // [ start1, stop1, start2, stop2, ... ]
@@ -135,7 +145,7 @@ function update_pump(temp, max, time) {
   status.tick_pump++;
   print("[POOL] update_pump", status.tick_pump, "- temp:", temp, "max:", max, "time:", time);
 
-  let duration = compute_duration_filt(max);
+  let duration = compute_filtration_time(max);
   let schedule = compute_schedule_filt(duration);
 
   print("[POOL] update_pump - duration:", duration);