It takes longer for the hot water to show up because, first, it has to start up, which takes a few seconds, and second, because the water in the line is completely cold. With a tank, the tank is heating the water in the tank, and some amount of the water in the line.
The other issue is that they have minimum flow rates before they turn on. So, when I’m doing dishes, I have to keep a certain amount of hot water flowing or it will turn off, and the water goes completely cold again. I’ve had that problem in the shower, when switching from two shower heads to one – I think they sometimes just both go off.
The other issue I had was that the output vent wasn’t installed properly, so moisture from the outside was dripping back in and it ruined the heat exchanger. Make sure whoever is installing it really knows what they’re doing – there should be a moisture drain off the side of the output vent to capture that moisture and drain it out the side.
You’ll have to get annual maintenance, or do it yourself. That involves using a pump to pump white vinegar through the system for about an hour. We have a water softener and still have to do this annually.
Because of the drain issue, we ended up having to replace ours at about the 10 year point. That’s where you might have to replace a tank kind, but tankless are much more expensive and are supposed to last 20 years. We’ve replaced the tankless with new ones, properly installed, and hopefully they will last longer now.
You just adjust to the delay in hot water – I’ll get the shower going while brushing my teeth, so it’s ready to go when I am. I definitely use more water with a tankless, but much less natural gas, since I’m not keeping water hot literally all the time, when at work, on vacation, etc.
The endless supply of water is nice – we have a pretty big jacuzzi-style tub, and someone can take a bath while someone else is taking a shower, and there’s still an endless supply.
I would do it again for the reduction in energy use, even though I use more water. Water use is not really an issue in NJ, but CO2 is an issue everywhere.