Tankless Electric are NOT green or a good choice (except for serving one, lone fixture perhaps).
Tankless Gas/Propane atmospherically vented are usually not a good choice. (for concerns of IAQ)
Tankless Gas/Propane sealed combustion(with no pilot light, preferably condensing type) is the only type of tankless to consider but we feel they rarely make sense.
Most independent, well respected studies find that the payback for tankless are 20 years or more: Not cost effective. Other problems: Existing homes often need new infrastructure, more maintenance, most dont work with low flow fixtures, cold water sandwiches, lost supply during power outages, dependence on a non-renewable resource,a possible increase in overall energy use due to endless supply.
Many Energy Efficient experts prefer tank to tankless and most are now advocating Heat Pump Water Heaters which are the future of water heating. With efficiencies from 125-300% these water heaters often use less energy than the most efficient sealed combustion gas models.
Generally, with existing homes its best not to change existing infrastructure and simply upgrading in efficiency when its time for replacement makes the most sense. For new, homes we use solar with electric tank backup but will probably be switching to Heat Pump Water Heaters, whenever possible moving forward.
Just keeping it real!
Many of the Tankless are designed with the pipes up top and the electronics below:
Guess what happens when there is even a small leak up top?
There other consideration is the technology: it hasn't been paid for yet: Once it has, the tankless will be a lot cheaper, probably cheaper than an old fashioned tanked; there is less to them, will cost less to manufacture.
Hang loose a year or two.
Tankless water heaters are well worth it.
They are better installed close to the Bath, on the outside of the house,
And if the house is two story better off being on the 2nd story.
Generally, having two are well worth it, one issue that has come up is using hard water.
Hard water tends to corrode and clog the internal piper and connections, hence if used in
Conjunction with water softeners, they are terrific.
There are newer Technology based Tankless heaters available.
I have seen some homes with Bosch tankless heaters have been around and still running fine
For over a decade.
Hope this helps.
Its a tankless position, but I'm sticking to it.