I'm getting ready to replace my leaky old gas heater with a new Raypak digital 406 model. I've been searching the internet to find the best deal. In one website, I notice that there was a difference in the 406 model based on elevation: 0-2000 ft and 2000 - 5000 ft, and there is about a $150 price difference between the two. I'm at about 3700 ft. Other websites don't mention elevation at all in the description. Does this really make a difference?