Electric Tankless Water Heater Overview
An electric tankless water heater is ideal for point-of-use applications. It is easy to install (depending on the model), relatively inexpensive and can supply an endless amount of hot water.
A whole-house electric tankless hot water heater is an option but the power requirements for units large enough to provide hot water for a typical household tends to outweigh most of the benefits of going with a tankless system.
Electric tankless water heaters generally cost 10-20% less to operate than comparable tank-type water heaters.
Point-of-Use Electric Tankless Water Heater
Electric tankless hot water heaters are ideal for point-of-use applications and will save energy (and money) if you frequently use relatively small amounts of hot water at certain outlets within your home.
Most of the smaller models are specifically designed for point-of-use applications and are usually quite small in size and output. They are ideal for under sink and other single point applications like a half bath, bar or vanity sink, workshop etc.
They are especially useful as an add-on or boost to an existing conventional or tankless system that:
a) is located a good distance from the outlet and only requires frequent and small amounts of hot water.
b) cannot meet the demands of a new renovation/addition and subsequent added demand.
In cases where a renovation or addition to a home includes higher demand outlets (e.g. a master bath) many have opted to use a whole-house electric system to service specific areas within the addition rather than extending their existing water heater's capacity and reach.
Whole House Electric Tankless Water Heater
With lower efficiency and flow rates than their gas counterparts, whole-house electric water heaters are best suited for just a handful of situations where demand is low, the distance between outlets is short, and temperature rise is minimal.
Temperature rise requirements (output temperature minus inlet temperature or incoming water temperature) is a big factor with whole-house electric systems. Most are just not powerful enough to meet high temperature rise requirements with an adequate maximum flow rate, especially when average inlet temperatures are below 60°F. (50°F is considered the average ground water temperature in the U.S)
Electric tankless water heaters are very high power appliances and often (depending on the model) require a home to have a 200 AMP, 240V electrical service. As a result, most existing residential wiring will likely not be able to support a whole house electric system that can service multiple uses, so you need to factor in extra cost for installation.
Keep in mind that with new construction designed with a tankless system in mind, the additional cost will be minimal if there is any at all. Also, smaller whole-house units in warmer climates can sometimes be installed on 100, 125, or 150 AMP electrical services.
The bottom line with all tankless systems, and electric whole house hot water heaters are especially sensitive to this is:
To illustrate the point, let's look at the specs for a particular model of electric tankless water heater.
| Temperature Rise | Flow Rate (GPM) |
|---|---|
| 45°F | 4.0 |
| 50°F | 3.7 |
| 60°F | 3.0 |
| 70°F | 2.6 |
| 80°F | 2.2 |
Depending on our temperature rise requirements we can see that just a 25° difference in incoming water temperature can significantly cut our flow rate from 4.0 to 2.6 GPM presuming that our desired output temperature remains constant.
And, if we want our minimum flow rate to be 3.7GPM then our maximum temperature rise has to be less than 50°. So if we want our hot water heated to 120° (which is the norm) our minimum incoming water temperature needs to be 70°.
One way of solving this issue if you're set on installing an electric tankless water heating system is a multi-unit or series install so that the temperature rise requirement is handled by two or more units.
The first takes the incoming water and warms it for the second unit that brings it up to the desired output temperature.
The consensus among experts and users seems to be that as a whole-house system, a single unit installation of an electric tankless water heater doesn't quite meet the expectations of the average North American. However, as a point-of-use system and for certain specific larger applications it can be your ideal choice.
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