Prepping for an On-Demand Hot Water Heater - Amps

Zebraitis · Jan 1, 2022

Hi folks.

I'm asking so that I can do some planning, and then hire a local electrician to do the work.

WHAT: This is my first question, ever, on this forum. I've joined so that I can understand better what I have in my home so that I do not run the risk of putting too great a load on my system.

I want to understand how many Amps my in-garage Load Center has going to it. (Please forgive me if my use of terminology may not be correct, as I am a DIY'er.)

WHY: My new On-Demand hot water heater (29Kw Atmore) requires 3 @ 40A DP 240v breakers. And... if I don't provide enough power these things tend to have the lights pulse when they are heating up their elements.

Here goes:

The home in the FL panhandle has 200A 240V service coming to it. I have verified that by looking up the permits for this property.

The meter on the outside of the home has a breaker panel built into it. In that panel are installed three DP breakers: one very small, one powering my Heat Pump, one for my load center (the only load center for the home)

The wires going to my load center are from the double-pole 90 amp breaker. There are some heavy duty aluminum wires (3) that are involved: One to one leg of the 90 amp breaker, one to the other leg of the 90 amp breaker, and one to ground.

The size of the wire, color and striping is the same that supplies power to the load center in the garage. That load center has the breakers for the home in it.

In the configuration as expected (line, line, ground) I have the wires coming to the load center. One line to one side of the GE load center, one line to the other, the third grounded.

So finally, my question:

Do I have 200 Amp service coming to the house with 90 Amps at the load center... or do I have 200 Amps coming to the house with 180 Amps in the load center?

Thanks.

James · Jan 1, 2022

That heater will require 120A at 240v
it is done by using 3 circuits at 40A each.

you really need to get an electrician round to check if you have enough power in the building to supply the heater and everything else in the house at the same time.

Zebraitis · Jan 1, 2022

James,

Thank you for your reply.

I understand this. But step #1 is requesting an answer to my question:

Does that DP 90A breaker in the meter box panel provide 180 amps to the load center?

I don't believe that a home built in 2005 would have just a 90A Load panel for the whole home.

As it is a small home, the number of breakers is relatively low... and it already has one DP breaker for a more traditional electric HWH installed. If the panel is 180 Amp, I would pull that breaker out, and add the other two.

However, if that isn't 180 Amps there, then I would need to pull a cable from the meter breaker box to the location where I will have the ODWH and put a load center there. And that becomes a substantially more costly event.

As I said, this is a planning question, not a doing question... so I am trying to understand for how much I need to budget: either three short runs across the garage, or a serious cable across the whole house.

I'm attaching pictures of the meter box and load center, if that helps.

Megawatt · Jan 3, 2022

Zebraitis said:
Hi folks.

I'm asking so that I can do some planning, and then hire a local electrician to do the work.

WHAT: This is my first question, ever, on this forum. I've joined so that I can understand better what I have in my home so that I do not run the risk of putting too great a load on my system.

I want to understand how many Amps my in-garage Load Center has going to it. (Please forgive me if my use of terminology may not be correct, as I am a DIY'er.)

WHY: My new On-Demand hot water heater (29Kw Atmore) requires 3 @ 40A DP 240v breakers. And... if I don't provide enough power these things tend to have the lights pulse when they are heating up their elements.

Here goes:

The home in the FL panhandle has 200A 240V service coming to it. I have verified that by looking up the permits for this property.

The meter on the outside of the home has a breaker panel built into it. In that panel are installed three DP breakers: one very small, one powering my Heat Pump, one for my load center (the only load center for the home)

The wires going to my load center are from the double-pole 90 amp breaker. There are some heavy duty aluminum wires (3) that are involved: One to one leg of the 90 amp breaker, one to the other leg of the 90 amp breaker, and one to ground.

The size of the wire, color and striping is the same that supplies power to the load center in the garage. That load center has the breakers for the home in it.

In the configuration as expected (line, line, ground) I have the wires coming to the load center. One line to one side of the GE load center, one line to the other, the third grounded.

So finally, my question:

Do I have 200 Amp service coming to the house with 90 Amps at the load center... or do I have 200 Amps coming to the house with 180 Amps in the load center?

Thanks.

You have a 200 amp main service and feeding a 90 amp sub panel. You are not using probably 50 amps max for your whole house so if your concerns about overloading your panel or panels is not going to happen. I’ll explain this to you that you have different calculations for the breaker size which is called your calculated load and the wires is called your connected and trust me that let’s say a 30 amp breaker probably is probably pulling 20 amps at max. You hire an electrician and you will have no worries and good luck