Electric Tankless Water Heaters

I have recently been doing some pretty intense research into Electric Tankless Water Heaters.  I did a 2 part series about Tankless Water Heaters in general a while back, but I didn’t talk much about Electric tankless except to say that they don’t seem to make much sense.

Well, at the risk of making all the Electric tankless manufacturers mad, what I found out in my research just confirmed that they really don’t make much sense.  I just have more information now as to why not.  Since tankless water heaters are being marketed so heavily right now, I wanted to give you the bottom line on what the marketing may not tell you.  Then at least you will be able to make an informed decision if you are considering tankless.

Tankless Basics

First of all, it is important to understand the basic operation of a tankless water heater.  All tankless heaters, whether electric or gas, use the same basic process to heat water.

1)When a hot water faucet is opened this causes water to flow through the tankless unit.

2) When the volume of flow is enough to trigger the unit to come on it begins heating water.

3)The amount of water that the heater allows to flow through is regulated by the desired outlet temperature.

4)This is, in turn, affected by the temperature of the incoming water.  The colder the incoming water the more heat the heater has to create.

Temperature Rise and Gallons Per Minute

That’s why the performance of tankless water heaters is measured by how many gallons per minute (GPM) the heater will deliver at a desired Temperature Rise.  The greater the desired Temperature Rise, the less Gallons per Minute of hot water can be produced.

How many GPM a tankless heater can deliver is entirely dependent on how much energy (either electric or gas) the unit has available to heat the water.  If you want more hot water you have to use more energy.  In a gas tankless this means more BTUs.  In an electric tankless this means more kilowatts, which also means a bigger amperage draw.  There is no way to get around this, it’s just the way it is.

Electric vs. Gas

Since we are talking  about electric tankless, the only thing I will say about gas models is that they almost always have better performance than electric models.  The “largest” electric tankless heaters can’t match the output of a “standard” gas tankless unit.  For the record, “regular”, tank type water heaters have the same differences.  Gas units just heat water faster than electric, tankless or otherwise.

How Much Hot Water Is Enough?

Now that you know the basic concepts, here’s why I don’t think an electric tankless is a good idea:

The largest unit I could find is only capable of delivering around 5 GPM (gallons per minute) at a modest 50° temperature rise.  At a 60° rise this drops to 4.3 GPM.  By the way, the only people I know who recommend using a 50° temperature rise when sizing a heater are the tankless manufacturers themselves.  Every plumber I know uses 60° as a minimum, real world figure.  Another thing to keep in mind: the Plumbing Code requires “hot water” to all fixtures for “bathing, washing, culinary purposes…etc.  The Code defines “hot water” as “greater than or equal to 110° F”.

OK, if all of these numbers are making your head hurt here’s the bottom line.  A standard shower head uses at least 2.5 GPM (gallons per minute).  The biggest residential electric tankless can deliver less than 5 GPM at a realistic temperature rise.  That means if two shower heads are running at once they will have less than full flow.  Since one of the most common complaints I hear is that the showers don’t have enough pressure already, this is just a recipe for dissatisfaction.


But that’s not all.  This lackluster performance comes with a price.

How Much Electricity Is Enough?

Electric tankless water heaters require an enormous amount of electricity as compared to any other equipment in the home.  The largest models require a whopping 160 amps. With most new homes having a 200 amp electrical service, that’s 80% of the total electrical capacity of the home.  Many older homes don’t even have a large enough electrical service to power the tankless, much less the rest of the house.

In case you think I’m just ranting, I’m not alone.  Electric Utilities hate
Electric Tankless Water Heaters by Reviewsicon .  Since they make money selling electricity you would think they would love them.  It seems that they use so much power that they can overload the system.  Check out this excerpt from one power company’s website on tankless:

“o  The new load of a tankless water heater can sometimes equal the load of an entire new home!

o  …if a customer installs a tankless water heater, the increased electric demand may exceed the design specifications of the system and require an upgrade of the cable and transformer. … will be charged directly to the customer. & If a customer installs a tankless water heater, the customer is required by approved tariff in both the Carolinas and Florida to pay the full cost to upgrade their facilities (including cable and transformer) to meet the need.

o  Customers complaining about a voltage fluctuation or flickering lights may be seeing the impact of a tankless water heater in their neighborhood. It is important to note that this voltage fluctuation may be noticed by other customers in addition to the customer with the tankless water heater – since several customers often share a single transformer. An investigation of all customers on the transformer may be necessary to determine the source of the problem.   If voltage problems exist because of a tankless water heater and a facility upgrade is necessary, the customer with the tankless water heater is required to pay the full cost to upgrade prior to construction.”

I don’t know if this is actually enforced but it is pretty plain to see that this Power Company is definitely trying to discourage the use of electric tankless water heaters.

Look, I do not have an axe to grind against the electric tankless industry.  There are even a few situations where a small electric tankless might make sense.  I just don’t think they are a good choice for a whole house water heater.  I also want to make sure that you can count on me to give you the real, no hype truth.  And, in this case,  I think electric tankless water heaters are a bad choice in most cases.

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