http://www.eere.energy.gov/consumer/...ting/index.cfm...

also note this word of warning

For example, taking a shower and running the dishwasher at the same
time can stretch a demand water heater to its limit. To overcome this
problem, you can install two or more demand water heaters, connected
in parallel for simultaneous demands of hot water. You can also
install separate demand water heaters for appliances--such as a clothes
washer or dishwater--that use a lot of hot water in your home.

then 2 showers and a dishwasher at same time will require multiple
tankless?

it also points out that a tankless with a pilot light can wipe out any
savings.....

wonder if the posters here who say their tankless works in a power
failure have tankless with pilot light? if so they arent saving
anything......

given the tankless high BTU and the flue gas requirements wonder how
many could afford multiple tankless around their home????????