Tankless electric water heaters

[redeemed1]

Hello my name is Augie. How can I accurately do a load calculation for a dwelling unit with an existing 225 amps and the homeowner wants to add 2 electric tankless water heaters? Are the tankless water heaters derated as a fastens in place appliance? Or do we calculate them in at 100% with no derating. Thanks


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[augie47]

(from another Augie).. IMO, You can apply 220.53 if they are part of 4 fixed appliances

 

[david]

There may be actual load data from the power company that could assist you in determining if this additional load can be added to the service

 

[blkmagik21]

Those things are ginormous power hogs. If they are adding two tankless heaters expect to upgrade the service like 80-90 percent of the time. I’ve seen one of those draw 200 amps on its own. When it turns on you can go outside and watch the electric meter spin


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[MAC702]

I'm not sure I'd want to derate anything for just those. You KNOW they will both be on at the same time, many times.

 

[kwired]

I'm not sure I'd want to derate anything for just those. You KNOW they will both be on at the same time, many times.

220.53 allows 75% demand factor for four or more appliances, not including ranges, dryers, space heating/cooling equipment. I don't see these as a type of load that will be continuously at maximum current and such demand factor shouldn't result in significant overloading.