I hope this answers your question on how long the propane tank will run the      
Westy Dometic fridge. 

        Propane Gas produces the following; 
        ----------------------------------- 
        1 pound of propane produces 21591 BTU's 
        1 gallon of propane produces 91690 BTU's 
        3 gallons of propane produces 275070 BTU's  (Westy tank is 3 gallons) 

        Dometic fridge uses 650 BTU's per hour on high (max) 

        soooooooo... 

        275070 BTU's in a 3 gallon tank / 650 BTU's per hour used for fridge 

        = 423 hours (or 17.5 days) 

Richard - 85 Westy 118K 

richard@bally.com