How many amps does a tankless water heater draw?

Beginner Info, Tankless Water Heater

how many amps does a tankless water heater draws
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In recent times, tankless water heaters have garnered loads and loads of hype, all because of their ability to provide you with an endless supply of hot water.

But, at the same time, you need to be well aware of the prerequisites including how many amps does a gas tankless water heater draws.

An electric tankless water heater most probably will require an upgrade in electric service.

  • A tank water heater with 4,500-watt elements operates on #10 wire and a 30-amp circuit breaker
  • One whole-house tankless water heater has four 7,000-watt elements, for a total electrical load of 28,000 watts. This load requires wire and a circuit breaker that will handle at least 120 amps at a cost many times that of electrical service to a conventional tank water heater

So, how many amps does a tankless water heater draw?

Well, the average electric tankless water heater needs at least 120 amps to operate.

Unfortunately, the average household’s total capacity is 200 amps.

What it actually means is, you’ll have to upgrade your electrical system to accommodate for the larger load demand.

Not only that but also the load would be requiring a large and more expensive meter loop and main panel for the house.

However, in some cases, you as an end customer might have to pay for the wiring between the neighborhood distribution transformer and the electric meter.

Tankless heaters can draw anywhere from 42 amps to 167 amps.

Well, you can calculate yourself how many amps does your tankless water heater draw.

Let’s have a quick look at the calculation.

In general, electric tankless water heaters can have a power input from 10, 000 watts (10 kW) to 40, 000 watts (40 kW).

In order to reduce the amp draw, almost all the electric tankless water heaters operate on a 240-volt circuit.

Using the electric power equation (P = I×V), we can calculate the by expressing the I or electric current like this:

(amps) = P (watts) / V (volts)

Example: Let’s say we have a 30 kW tankless water heater on a 240-volt circuit. How many amps does a 30 kW tankless water heater use? We use the electrical power equation in this way:

(amps) = 30,000W / 240V = 125 amps

Such a heater draws 125 amps (you need several 20-amp or 30-amp breakers for installation).

The below table is self-explanatory about the number of amps that your tankless water heater will draw and is based on the aforementioned calculation.

Tankless Heater Size (in kW) Electrical Current (in Amps)
 10 kW 42 amps
 11 kW 46 amps
 12 kW 50 amps
 13 kW 54 amps
 14 kW 58 amps
 15 kW 63 amps
 16 kW 67 amps
 17 kW 71 amps
18 kW75 amps
19 kW79 amps
20 kW83 amps
21 kW88 amps
22 kW92 amps
23 kW96 amps
24 kW100 amps
25 kW104 amps
26 kW108 amps
27 kW113 amps
28 kW117 amps
29 kW121 amps
30 kW125 amps
31 kW129 amps
32 kW133 amps
33 kW138 amps
34 kW142 amps
35 kW146 amps
36 kW150 amps
37 kW154 amps
38 kW158 amps
39 kW163 amps
40 kW167 amps
HVAC Metrix

SEER = (1 × EER100% + 42 × EER75% + 45 × EER50% + 12 × EER250%)/100

EER = BTUcooling/W

HSPF = BTUheating/W

COP = Q (useful heat)/W (input work)

ACH = CFM x 60/Area x Heightceiling

Total Heat (BTU/hr.) = 4.5 x CFM x Δh (std. air)

Sensible Heat (BTU/hr) = 1.1 x CFM x Δt (std. air)

Latent Heat (BTU/hr) = 0.69 x CFM x Δgr. (std. air)

1 HP = 746 Watts

1 kW = 3413 BTU

So, you might be wondering that how can I check whether my home electric system needs to be upgraded or NOT, right?

Well, whether you’re a first-time buyer or a seasoned professional, the best thing that you can do is to hire a certified technician and get thorough feedback about your home electric system in order to refrain from any last-hour misadventure.

 Just for your information, if you’re planning to replace your conventional water heater with a tankless counterpart in the existing home then the installation cost would be much higher than it would’ve been if you would’ve installed the tankless heater in a new home. 

So, what will happen if I’ll install the new tankless water heater without upgrading my home electric system?

Definitely, an interesting as well as experimental question that isn’t so easy to reply to, if at all you don’t have prior experience with the installation of a tankless heater.

Well, low voltage or sudden voltage drops are likely to result in dimming or blinking lights, and you might expect some other problems as well.

In simple words, the user experience, convenience, performance, and efficiency would be impacted adversely.

 Trust me, in the past, I’ve come across problems such as blinking lights, and after doing root cause analysis, I came to know that connecting 28-kW tankless units in homes with 150-amp services on 10-kW transformers was a mistake on my end. 

Gas Tankless vs. Electric Tankless: Which model requires up-gradation of a home electric system?

In simple words, it DEPENDS.

But, I’m sure you’re not here to ACCEPT this answer, right?

Let’s do some more research and dig a little more into the topic.

Frankly speaking, as per my knowledge and experience, I can affirm that a gas tankless generally does not require up-gradation of home electric system serves as an electric tankless does.

Moreover, you also need to be aware of the fact that most of the gas tankless water heaters that we’ve reviewed on this blog are energy star certified and many of them are even qualified for the federal tax rebates.

Nonetheless, the energy star label doesn’t mean that traditional heaters are completely useless when it comes to evaluating a unit on efficiency parameter.

How many amps does a Rinnai tankless water heater use?

Frankly speaking, Rinnai tankless water heaters are one of the best in their category.

Time and again, the brand has proved its mettle by providing cost-effective, high-efficient products including tankless water heaters.

Rinnai Tankless Water Heaters require 120 volts AC, 60 Hz, and less than three amps.

Are tankless water heaters 110 or 220?

Well, you’ll find tankless water heaters in both the models, that is, 110V and 220V.

So, you can choose the one that syncs well with your home electricity requirement.

The small tankless version, that is, the point-of-use or under-sink tankless heaters draws mostly 110V.

However, the powerful tankless heaters that are meant for commercial purposes, definitely draw more voltages.

How many amps is a 50-gallon water heater?

A typical electric tankless water heater works runs at 4500 watts.

Many of you might not be well-versed with the fact that in an electric circuit of 240 volts, 4500 watts is equivalent to 18.75 amps.

Are most hot water heaters 220?

Most electric hot water heaters operate on 220 to 250 volts AC.

So, if you’re planning to buy a tankless water heater for your home that comes with 220 volts, then you should know that this voltage in a home requires a double circuit breaker rated for the amperage draw of the hot water heaters.

How many BTUs do I need for a tankless water heater?

In order, to get the water to a sufficient temperature, the units definitely use a high volume of gas, typically between 150,000 and 200,000 BTUs, which simply means that an average home would be requiring the upsizing of the gas line.

How many amps does an electric hot water heater use?

Most of the electric tankless hot water heaters that we’ve reviewed so far on our blog typically require a dedicated 30-amp, 240-volt breaker.

Electric water heaters require a 240-volt dedicated circuit, which serves only the water heater and no other appliances or devices.

The circuit wiring typically includes a 30-amp double-pole breaker and 10-2 non-metallic (NM) or MC cable.

What size breaker do I need for a 40-gallon electric water heater?

Frankly speaking, your average residential 30 or 40-gallon water heater is somewhere around 4500 watts, and if I’m NOT wrong, then they usually go on a 30 A breaker.

What size breaker do I need for a 4500-watt water heater?

Since this is a purely resistive load 5500 watts at 240 volts is 23 amps, the breaker is sized at 30 amps and 10 AWG wiring is used.

In your case if the elements are strapped for 4500 watts draw is 18.75 amps, permanent draw loads should be sized at 80% of breaker capacity so a 20 amp breaker is limited to 16 amps.

What size breaker do I need for a 3000-watt water heater?

A 3000 watt 240 volts can be operated on a 14/2 cable, 15 amp double pole breaker.

What size breaker do I need for a 7500-watt heater?

7500 watts / 240 volts = 31 amps , so 40 amp breaker is needed.

What size breaker do I need for a 5500-watt water heater?

The math shows that a 5500-watt water heater is well within the safe maximum for a 30 amp breaker and 10 gauge wire.

When heat exceeds circuit breaker rating, then the breaker trips.

A 30 amp breaker with 10 gauge wire has an 80% safe maximum = 24 amps. 24 amps x 240 volts = safe maximum 5760 watts.

Does an electric water heater require a disconnect?

According to the NEC, an electric water heater does not require any disconnect other than a circuit breaker at the main panel or sub panel and it does not need to be insight.

Wrapping Up

First of all, I would like to thank you for being with us till the end.

Secondly, I would like to bring to your notice that I along with my core team have tried to the best of our capabilities to answer some of the frequently asked questions including how many amps does a tankless water heater draws in the best possible manner that we could.

And, in case, you liked our efforts and want to appreciate us, then all you need to do is to share this piece of information with the ones who are in need of it.

After all, sharing is caring, isn’t it?

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