I have a old apollo hydroheat system where the water heater/boiler is located on the middle floor of a townhome next to an exterior wall (the closet is small and located in the kitchen area). the water heater was a direct vent model and vented thru the side wall a few inches above the WH. Can i replace the water heater with standard vent model (same as natural vent I assume)? I wanted to keep the direct vent model (State Select) but apollo is out of business and the new State model is taller. In the blog it seemed that you stated that a natural vent cannot go thru the side wall. Note we live in Illinois. I keep getting conflicting information so any guidelines would be helpful.