The range of noritz tankless water heaters is among the best money can buy. There is a unit in their range that can cope with pretty much any household, and a tradition of quality that few can match.
This company, which started life in Japan, is the biggest maker and vendor of tankless gas hot water heaters in the world. Though Japanese born and bred they now have a US subsidiary and this caters directly to the North American market (they have similar operations in the other big gas tankless areas like the UK, Europe, New Zealand and Australia).
The key to sizing tankless hot water heaters is to know your household peak flow - this is the maximum demand for water and usually occurs at any time you have more than one appliance (including showers and faucets) needing water simultaneously.
The gas tankless water heater from Noritz come sized by gallons per minute. The smallest unit runs up to 6.3 gallons per minute and could fairly comfortably handle a couple of applications simultaneously. The largest model, the N132m which can put out a massive 13.2 gallons of hot water each minute (hence the model number 132).
With Noritz products you are buying instant hot water heaters with a long history of quality functioning behind them.