diff --git a/optihood/buildings.py b/optihood/buildings.py
index c39185c..cf30808 100644
--- a/optihood/buildings.py
+++ b/optihood/buildings.py
@@ -880,9 +880,14 @@ def addStorage(self, data, storageParams, ambientTemperature, opt, mergeLinkBuse
                         self.__nodesList.append(storage.getStorageLevel(i))
                         self.__nodesList.extend(storage.getDummyComponents(i))
                 elif "iceStorage" in s["label"]:
+                    if not np.isnan(s["initial capacity"]):
+                        initial_ice_frac = float(s["initial capacity"])
+                    else:
+                        initial_ice_frac = 0
                     self.__nodesList.append(IceStorage(label=storageLabel,input=self.__busDict[inputBusLabel],
                                                        output=self.__busDict[outputBusLabel],
                                                        tStorInit=float(storageParams["ice_storage"].at[s["label"],"intitial_temp"]),
+                                                       fIceInit = initial_ice_frac,
                                                        fMax=float(storageParams["ice_storage"].at[s["label"],"max_ice_fraction"]),
                                                        rho=float(storageParams["ice_storage"].at[s["label"],"rho_fluid"]),
                                                        V=float(s["capacity max"])/1000, # conversion from L to m3
diff --git a/optihood/storages.py b/optihood/storages.py
index 7dff0ad..388aa99 100644
--- a/optihood/storages.py
+++ b/optihood/storages.py
@@ -304,10 +304,13 @@ class IceStorage(on.Node):
     inflow_conversion_factor: efficiency of heat exchanger at the inlet of the ice storage
     outflow_conversion_factor: efficiency of heat exchanger at the outlet of the ice storage
     """
-    def __init__(self, label, input, output, tStorInit, fMax, rho, V, hfluid, cp, Tamb, UAtank, inflow_conversion_factor, outflow_conversion_factor):
-        if tStorInit <= 0:
-            raise ValueError("The initial temperature of ice storage should be greater than 0°C, i.e. without any ice formation.")
+    def __init__(self, label, input, output, tStorInit, fIceInit, fMax, rho, V, hfluid, cp, Tamb, UAtank, inflow_conversion_factor, outflow_conversion_factor):
+        if tStorInit < 0:
+            raise ValueError("The initial temperature of ice storage should be greater than or equal to 0°C.")
         self.tStorInit = tStorInit
+        if fIceInit < 0 or fIceInit > 1:
+            raise ValueError("The initial ice fraction in ice storage should be in [0,1]")
+        self.fIceInit = fIceInit
         if fMax < 0.5 or fMax > 0.8:
             raise ValueError("Maximum ice fraction should be defined within the range 0.5-0.8")
         self.fMax = fMax
@@ -409,7 +412,7 @@ def _initial_ice_state_rule(block):
             """
             for g in group:
                 lhs = self.mIceStor_prev[g,0]
-                rhs = 0
+                rhs = g.fIceInit*g.rho*g.V
                 block.initial_ice_state.add((g, 0), (lhs == rhs))
 
         self.initial_ice_state = Constraint(group, m.TIMESTEPS, noruleinit= True)