Types of Electric TWH’s
Whole-house tankless units are intended for whole-house, multi-fixture applications and offer better functionality than their POU counterpart.
Point-Of-Use or "under-the-sink" electric tankless water heaters are compact units designed for single-fixture use, most commonly for a kitchen, laundry, bar or bathroom sink. They are inexpensive and very compact, but often lack advanced functionality, such as temperature adjustment, modulation, etc.
Mini-tank electric water heaters are not considered true "tankless" since they incorporate a small storage tank. However, due to their relatively small size, they are also classified as under-the-sink water heaters and are intended for single fixture applications. Most of these are 120V plug-and-play type, which means no complex wiring or piping is needed.
Sizing an Electric Tankless Water Heater
Sizing for each of the above-mentioned water heaters will differ and we suggest visiting each page for particular details.
In general, all tankless heaters work based on a principle where the unit will add a certain amount of heat to the water flowing through it. The higher it's wattage - the more heat can be added. This number is dependent of two main factors - incoming water temperature (cold/groundwater) and the flow of water through the unit. Some (whole-house) units will prioritize the outgoing water temperature over flow rate, and can limit the flow to meet the desired temperature. Others (many POU's) disregard flow and only add a fixed amount of heat, either requiring a flow limiting device (often included) or leaving calculations fine-tuning of the end user.
Availability (uptime) and abundance of electricity are also important factors, especially for whole-house units, which usually require 208-240V power supply and several dedicated high-amp breakers.
