Wiring a tankless water heater

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Old 11-25-18, 03:57 PM
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Wiring a tankless water heater

I was looking at an Ecosmart tankless electric water heater.Model 18. It needs 2 40 amp 240v breakers.Whoa!
Would you install a 100 amp subpanel if your main panel was mostly full??
another question...do you think this would use more juice per month than a 40 ga electric standard tank for the same amount of usage ?
 
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Old 11-25-18, 04:19 PM
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What size is your main panel ?
Based on other large loads..... 100A may not be large enough to support that tankless heater.
You need to consider things like electric heat, electric range, electric dryer, etc.

Since there are no standby losses it should use less power.
However.... there really is no way to know for sure without trying it.
 
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Old 11-25-18, 05:51 PM
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I was looking at an Ecosmart tankless electric water heater.Model 18. It needs 2 40 amp 240v breakers.
That's a medium sized unit, most units require 3 - 40 amp breakers. Before you buy it be absolutely certain it is sized properly or you could be faced with just having warm water when you want hot. Personally, I wouldn't want the additional maintenance required for a tankless unit.
 
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Old 11-26-18, 06:24 AM
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do you think this would use more juice per month than a 40 ga electric standard tank for the same amount of usage ?
That will depend on how much water you use. There will be less difference if you use a lot of water and more difference if you don't.
Unless you live down south, I don't recommend electric tankless. It will have hard time heating up cold water in Winter.
Also, that tankless water heater is designed to heat up to the temperature you will actually use at the faucet without mixing cold water. Meaning you can wash and take shower at full hot.
The problem is, many shower valves do not allow full hot even with temperature limit set all the way.

You might also have to replace shower head and faucet aerator to smaller gpm (water saver) to allow enough time for water to heat up.
 
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Old 11-26-18, 06:57 AM
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(copied from another forum) Run the incoming cold water for the water heater through several feet of finned pipe dissected out of baseboard FHW radiators. This will preheat the water and can allow a medium "power" tankless heater to work where you might otherwise need a high "power" heater. (Both kinds of heaters use the same 240 volts.) Install the finned pipes on the wall or ceiling out of reach of people's heads and shoulders.

It is not necessary to install a subpanel if the needed breakers (two or three double wide doubles) for the water heater will fit in the existing panel. But you will always need to do a load analysis for the whole house to determine if the the panel and/or service needs upgrading. A medium power tankless electric heater might work with your existing electrical service where a high power heater might require a service upgrade.

When the heater needs two (or three) 40 amp branch circuits you may not connect it to a single 80 (or 120) amp branch circuit.
 
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Old 11-26-18, 11:01 AM
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I have very small hot water needs.
I am not going to disconnect other breakers to fit in 2 40 breakers so
I need a sub. I will remember to unbond the neutral.

I was thinking about having several options for hot water. If I can get units really cheap. I will keep my 50 ga for a future owner.
I will have a gas tankless when someone makes one for a fair price out of welded stainless steel.
And I will install an Ecosmart if they drop the price after Xmas.
My hot water needs are as small as you find in America.And our northern plains electricity is cheap. I use about 30 $ a month.
 
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Old 11-26-18, 11:38 AM
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I am not going to disconnect other breakers to fit in 2 40 breakers so
I need a sub.
It's often easier to put the higher-load breakers in the main, and move a couple smaller loads to a subpanel.

If you run your water heater off the sub, you'll need a 100A breaker, 100A sub panel, and will pretty much have it maxed out.

If you free up some spaces in your main, you can probably get away with a 60A breaker for your subpanel, and have extra spaces/capacity for future circuits.

Granted, one isn't better than the other - just ideas for the future.
 
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