diff --git a/cara/apps/calculator/static/js/form.js b/cara/apps/calculator/static/js/form.js
index 862b9f8c..be07f497 100644
--- a/cara/apps/calculator/static/js/form.js
+++ b/cara/apps/calculator/static/js/form.js
@@ -49,6 +49,12 @@ function require_fields(obj) {
       require_air_changes(false);
       require_air_supply(true);
       break;
+    case "interval":
+      require_venting(true);
+      break;
+    case "always":
+      require_venting(false);
+      break;
     case "hepa_yes":
       require_hepa(true);
       break;
@@ -142,6 +148,14 @@ function require_air_supply(option) {
   disable_input_field("#air_supply", !option);
 }
 
+function require_venting(option) {
+  require_input_field("#windows_duration", option);
+  require_input_field("#windows_frequency", option);
+  //TODO: Update this after merge 109
+  disable_input_field("#windows_duration", option);
+  disable_input_field("#windows_frequency", option);
+}
+
 function require_single_event(option) {
   require_input_field("#single_event_date", option);
   disable_input_field("#single_event_date", !option);
diff --git a/cara/apps/calculator/templates/calculator.form.html.j2 b/cara/apps/calculator/templates/calculator.form.html.j2
index e044d7c4..5d196701 100644
--- a/cara/apps/calculator/templates/calculator.form.html.j2
+++ b/cara/apps/calculator/templates/calculator.form.html.j2
@@ -86,10 +86,12 @@
           <label for="window_hinged">Top- or Bottom-Hung</label>&nbsp;&nbsp;<br>
         Width of window: <input type="number" step="any" id="window_width" class="non_zero has_radio disabled" name="window_width" placeholder="meters" min="0"><br>
         Opening distance: <input type="number" step="any" id="opening_distance" class="non_zero" name="opening_distance" placeholder="meters" min="0"><br>
-        Windows open: <input type="radio" id="always" name="windows_open" value="always">
-                        <label for="always">Always</label> &nbsp;&nbsp;
-                      <input type="radio" id="interval" name="windows_open" value="interval">
-                        <label for="interval">10 min / 2h</label>
+        Windows open: <input type="radio" id="always" name="windows_open" value="always" onclick="require_fields(this)">
+                        <label for="always">Always</label>&nbsp;&nbsp;
+                      <input type="radio" id="interval" name="windows_open" value="interval" onclick="require_fields(this)">
+                        <label for="interval">Interval:</label>&nbsp;&nbsp;
+                      <input type="number" step="any" id="windows_duration" name="windows_duration" placeholder="mins" min="1" size="5" data-has-radio="#interval"> / 
+                      <input type="number" step="any" id="windows_frequency" name="windows_frequency" placeholder="hour" min="1" size="5" data-has-radio="#interval">
         <br>
     </div>