I'm in Ontario, Canada and I've used a cookie tin heater the last two winters.  I use it with a 5 gallon waterer and I found that I had to use two 75 watt bulbs in order to keep the water from freezing.  Both winters were pretty cold and the water froze if one of the bulbs blew.
	
		
			
		
		
	
				
			 
	 
 
		 
 
		 
 
		 
			
		
		
		
	
	
			
		 
 
		
 
 
		 
			
		
		
		
	
	
			
		 
			
		
		
		
	
	
			
		 
 
		 
 
		

 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		