Which Type of Tankless Water Heater to Use
There are two basic types of tankless water heaters, Point of Use and Whole House. The type you select is based upon your intended use. And your intended use will have even more to do with the cost of these units.
Point of Use Tankless Water Heater
I have a point of use water heater under my kitchen sink. It creates 170 degree F hot water instantly and I love the fact that I can get a cup of tea anytime I want (like now as I'm writing this). The point of use tankless water heater is relatively small and will usually fit inside a sink cabinet or in a closet. They are typically dedicated use heaters meaning the unit serves one sink / faucet or one shower, etc.
Point of use tankless water heaters are less expensive than whole house units and cost around a few hundred dollars for the unit (without installation).