diff --git a/homeassistant/__init__.py b/homeassistant/__init__.py
index 8bb4a0b8b1f..88066bca33e 100644
--- a/homeassistant/__init__.py
+++ b/homeassistant/__init__.py
@@ -30,8 +30,22 @@ TIMER_INTERVAL = 10  # seconds
 # How long we wait for the result of a service call
 SERVICE_CALL_LIMIT = 10  # seconds
 
-# Number of worker threads
-POOL_NUM_THREAD = 4
+# Define number of worker threads
+#
+# There are two categories of Home Assistant jobs:
+#  - jobs that poll external components that are mostly waiting for IO
+#  - jobs that respond to events that happen inside HA (state_changed, etc)
+#
+# Based on different setups I see 3 times as many events responding to events
+# then that there are ones that poll components. We therefore want to set the
+# number of threads to 1.25 of the CPU count, we will round it up so the
+# minimum number of threads is 2.
+#
+# We want to have atleast 2 threads because a call to the homeassistant.turn_on
+# will wait till the service is executed which is in a different thread.
+#
+# If os.cpu_count() cannot determine the cpu_count, we will assume there is 1.
+POOL_NUM_THREAD = int((os.cpu_count() or 1) * 1.25) + 1
 
 # Pattern for validating entity IDs (format: <domain>.<entity>)
 ENTITY_ID_PATTERN = re.compile(r"^(?P<domain>\w+)\.(?P<entity>\w+)$")
@@ -268,12 +282,12 @@ def create_worker_pool(thread_count=POOL_NUM_THREAD):
     def busy_callback(current_jobs, pending_jobs_count):
         """ Callback to be called when the pool queue gets too big. """
 
-        _LOGGER.error(
+        _LOGGER.warning(
             "WorkerPool:All %d threads are busy and %d jobs pending",
             thread_count, pending_jobs_count)
 
         for start, job in current_jobs:
-            _LOGGER.error("WorkerPool:Current job from %s: %s",
+            _LOGGER.warning("WorkerPool:Current job from %s: %s",
                           util.datetime_to_str(start), job)
 
     return util.ThreadPool(thread_count, job_handler, busy_callback)
@@ -347,9 +361,10 @@ class EventBus(object):
             if not listeners:
                 return
 
+            job_priority = JobPriority.from_event_type(event_type)
+
             for func in listeners:
-                self._pool.add_job(JobPriority.from_event_type(event_type),
-                                   (func, event))
+                self._pool.add_job(job_priority, (func, event))
 
     def listen(self, event_type, listener):
         """ Listen for all events or events of a specific type.