diff --git a/reoptjl/models.py b/reoptjl/models.py
index f0ccbe808..36a1485ca 100644
--- a/reoptjl/models.py
+++ b/reoptjl/models.py
@@ -5465,6 +5465,9 @@ class ASHPSpaceHeaterInputs(BaseModel, models.Model):
 
     def clean(self):
         error_messages = {}
+        if self.dict.get("min_allowable_ton") in [None, "", []] and self.dict.get("min_allowable_peak_capacity_fraction") in [None, "", []]:
+            self.min_allowable_peak_capacity_fraction = 0.5
+
         if self.dict.get("min_allowable_ton") not in [None, "", []] and self.dict.get("min_allowable_peak_capacity_fraction") not in [None, "", []]:
             error_messages["bad inputs"] = "At most one of min_allowable_ton and min_allowable_peak_capacity_fraction may be input to model {}".format(self.key)
 
@@ -5732,6 +5735,9 @@ class ASHPWaterHeaterInputs(BaseModel, models.Model):
 
     def clean(self):
         error_messages = {}
+        if self.dict.get("min_allowable_ton") in [None, "", []] and self.dict.get("min_allowable_peak_capacity_fraction") in [None, "", []]:
+            self.min_allowable_peak_capacity_fraction = 0.5
+
         if self.dict.get("min_allowable_ton") not in [None, "", []] and self.dict.get("min_allowable_peak_capacity_fraction") not in [None, "", []]:
             error_messages["bad inputs"] = "At most one of min_allowable_ton and min_allowable_peak_capacity_fraction may be input to model {}".format(self.key)