Frugal and Energy Efficient Living

Never run out of hot water - even when family visits. Can handle up to three showers at the same time. Reduced our gas bill by about $15.

And they're supposed to last twice as long, so in the end it should actually be cheaper.

Most of the challenges shouldn't impact you since it's already installed. They can be VERY expensive to install if you don't already have a large enough gas service... or need a new chimney or lots of plumbing. Ours is an exterior model, so it's self-venting and went in right next to our gas service (and saved space).

It can add a few seconds to the time it takes to get hot water at a faucet. For some people (especially on older models), there's a "cold water sandwich" effect that can be annoying. You get out of the shower and a couple minutes later someone else gets in and turns it on. The water in the pipes is already hot, so she gets right in. But the tankless was off and takes a couple seconds to kick back in... all while cold water runs through it. So you get a "sandwich" in the pipes of hot-cold-hot that hits her in the shower.

We've never run into it. The newer models kick in much faster if they've recently been on... and a clever installer can mitigate the problem with a small mixing tank.

Whether or not it can meet demand depends entirely on the size of the unit and that of your family. But it will never run out of water, so the worst case is taking turns.

The "expensive maintenance" can be done yourself if you're reasonably handy. You buy a 5-gallon bucket and a few gallons of white vinegar. You get a submersible pump and a couple lengths of hose (match up the inlet/outlet taps on the unit - they're probably standard hose fittings... so I used an old garden hose)... then you just cut off the water supply and drain the unit (turn a couple valves) and run vinegar through it for 30-60 minutes. Do that once or twice a year and you shouldn't have problems for decades. If you don't do it, you'll get less and less hot water from the unit and waste fuel (which may be why some people get less hot water than they expected).

After the initial outlay for pump/etc, it costs you a few dollars a year in vinegar and a couple hours of your time.

Best of luck!