Enough Power?


Old 07-08-17, 01:04 PM
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Enough Power?

I am in the planning stages of trying to update my Water Heater in my condo. I am trying to replace it with an Electric Tankless Waterheater.

The electric tankless waterheater is 36kW and has max draw of 150 AMPs. (And side note that a gas tankless heater is not an option)

My main breaker panel is 150A. I have enough open slots for the electric water heater.

My main question is the main breaker panel sufficient (specifically in regards to the AMPs) to add the tankless water heater?
Old 07-08-17, 01:10 PM
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Short answer: No.

You are not allowed to calculate usage assuming that you will have the discipline to not use much other stuff when someone is taking a shower and drawing from the electric tankless.

You need to do a load analysis.Rules and calculations are at the back of the NEC among other places I am not knowledgeable of. If the results, which include dedicating three watts for each square foot of living area, indicate need for a total of more than 150 amps (36,000 watts) then you need a new main panel and service entrance.
Old 07-08-17, 01:10 PM
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Welcome to the forums!

There is no chance your electrical service will handle that size of a load. Being a condo I doubt you will be able to upgrade your service as you will need likely a new 320 amp service brought in. (I doubt a 200 amp would even be enough depending the other loads in the condo) I recommend looking at other options.
Old 07-08-17, 01:36 PM
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That was sadly my assumption but I wanted to make sure before I discounted it. I appreciate the help!
Old 07-08-17, 05:49 PM
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Some would consider a tankless a downgrade not an an upgrade. Especially in situations like yours. Just the $2000+ installation costs for a new service means you won't save any money over a reasonable time. When you do eventually begin to break even you will be hit with repair costs that won't be cheap. Of course if you live in a multi person household there will be complaints because water flow has to be throttled or the temperatures begin to feel not warm enough. Tankless can only heat the water adequately as long as the volume and flow rate are low enough.

Why do want to change to tankless? Is there a specific problem with the storage type WH you have. Maybe the pros can advise you on that. A fix without going tankless.
Old 07-08-17, 11:05 PM
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I agree with Ray in that I would consider this a downgrade, and you certainly will not gain anything financially. But I do note that you were careful with your words and said "update", not "upgrade". Very appropriate choice of words.

If you like to take really long showers and find yourself running out of hot water, you can always crank up the temperature on your tank water heater which will solve the problem. Mine's hot enough to scald the devil himself and I could take an hour long shower if I wanted to. A bit wasteful, sure. But my electricity bill is not significantly different cost-wise at $0.115/kWh around here.

Some side benefits of tank-type heaters besides the obvious cost and ease-of-repair benefits: More and more utilities are switching to off-peak pricing, and with a tank you can take advantage of that. If the power goes out, you still have enough hot water for a shower the next day. Built-in emergency water supply for when the zombies take over.

I am dying to know what caused this desire to have a tankless. To the point where your only 2 options considered were tankless electric and tankless gas, with gas being impossible in your case. It almost seems like you want a tankless regardless of the cost, fuss, nor how well it's going to work. Why? Please tell me there's a nice looking sales girl in the tankless store or something like that!
Old 07-10-17, 08:26 AM
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This may not be an option for you, but instead of using one powerful tankless heater in a central location, you could wire 240V under each sink cabinet and use one small tankless heater per bathroom/kitchen. The smaller ones are also much cheaper to purchase (around $500-600) and have an advantage where if one breaks, it doesn't take out all the hot water in your entire house.

I am not an expert, but I assume if your household only takes one shower at a time (on an average night), it would be use less power per month using multiple small systems because they won't be on all at once.

Now, your original question would still be valid because you need to make sure your panel has enough amperage in case all your tankless heaters get turned on at once (I thinkyou have to consider 100% usage, but I'm not sure):

Say each tankless heater uses 30 AMPs and you have 3 bathrooms, 1 kitchen, & 1 laundry room (5 locations that require hot water). 30 * 5 is 150 AMPS, so you're back to your original problem of not having enough power for 150 AMPS.

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