If you overspec too much, it can cause the unit to cool down too quickly and short cycle somewhat. It's not ideal. 
I think our indoor units are 9k each. I have a 12k in my garden cabin. It is well insulated and works superbly.
	
		
			
		
		
	
				
			I think our indoor units are 9k each. I have a 12k in my garden cabin. It is well insulated and works superbly.
 
	 
  
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
					
				 
						
					 
 
		 
	 
 
		
