Most if not all gas tankless, vent with PVC now. It's not as bad as it used to be...don't buy Rennie...depending on your climate, some can be installed on an outside wall and directly vent outside. Pat can't unless he decides to move way south. The real expenses are the gas connection, valve kit and the heater itself. In Pat's case the 40 gal electric really is his best choice. I think I mentioned this but never do electric tankless. They require an insane amount of amps. Even with a newer 200 amp panel you blast through 60 amps with just one heater. If your house requires 2 heaters, you just lost 120 amps. In an all electric house you might have some brown outs or kill some sensitive electronics.