Gas is the only way to go tankless, I had one installed 3 years ago as it was about the same price as a direct vent water heater. If you have a regular vented heater now a tankless will be much more expensive. Don't believe the hype on the gas savings on the tankless as any savings on these is eaten up if you pay to have it cleaned every year. I purchased the sump pump and clean it myself but any savings over a tank is minimal. I do like the endless hot water though and much more compact than a tank. Warranties on tankless are 10+ years I believe.
Our new build has tankless water heaters (gas, Rinnai brand). It vents directly outside the garage wall and works well.
When the water is cold it takes quite a while for the water to get hot, that is the benefit of a tank water heater, you have water already heated.
But once the hot water starts flowing it is endless. We can take two showers at once, and run the dishwasher no problem.
They aren't too bad to clean yourself, takes about an hour and 3 gallons of vinegar. I have a little submersible pump, and some washer lines to pump vinegar through the system for about an hour.
Mine needs to be cleaned every year for sure with our hard water. I can always tell it needs to be done when I hear the burner making popping sounds, the deposits need to be removed.
For the OP, I think he needs to stick with a tank water heater. Converting to Tankless doesn't make financial sense, and if he is filling up big jacuzzi tubs during winter, tank would be the way to go.
I would not consider Electric tankless anywhere but Florida or Arizona. Even here in South Texas it still gets cold we have a gas furnace and gas water heater.
