Water Heaters

[mhudson2]

How do you calculate the tankless electric water heaters
Example - A tankless water heater with 4 - 40 amp circuits
Do you calculated as if it was just another fixed appliance.
Thanks

 

[Dennis Alwon]

IMO, that would calculate as an appliance just as a standard water heater would.

 

[Little Bill]

IMO, that would calculate as an appliance just as a standard water heater would.

Except the tankless is not a continuous load and a tank model is.

 

[LarryFine]

Except the tankless is not a continuous load and a tank model is.

It certainly can be; just leave the water running for three hours.

 

[mikeames]

Would the continue load status even matter in sizing the circuits? Still sized 80%/120% ? I suppose if the manufacture specifies 40a circuits then nothing else is needed for circuit sizing, but load calculation as the OP asks is what matters?

 

[Dennis Alwon]

Mixed up to threads in my response

 

[Dennis Alwon]

Except the tankless is not a continuous load and a tank model is.

In the load calculations for a service I have never seen a water heater used at 125%. You use either 5000 watts or higher. I assume the op was asking about a service so no it wouldn't matter Mike

 

[Dennis Alwon]

Would the continue load status even matter in sizing the circuits? Still sized 80%/120% ? I suppose if the manufacture specifies 40a circuits then nothing else is needed for circuit sizing, but load calculation as the OP asks is what matters?

In this particular case, and IMO, it doesn't matter but calculate for a branch circuit then the wire must be at 125% if it were continuous. I would think the manufacturer has it figured out here anyway

 

[mikeames]

at 125% if it were continuous.

Opps, I typed 80%/120% I knew better but the symmetry fooled my brain.

 

[Dennis Alwon]

Opps, I typed 80%/120% I knew better but the symmetry fooled my brain.

You could divide by 80% and still get the same result as multiplying by 125%

 

[Little Bill]

In the load calculations for a service I have never seen a water heater used at 125%. You use either 5000 watts or higher. I assume the op was asking about a service so no it wouldn't matter Mike

I assumed he was talking about the branch circuit since I didn't see "service" in the OP. I could be wrong.

 

[mikeames]

You could divide by 80% and still get the same result as multiplying by 125%

Absolutely I fully understand it thus why I expressed it that way, just typed the "0" instead of the "5"
80% is for max load for given circuit. 125% is min circuit of a given load.

I assumed he was talking about the branch circuit since I didn't see "service" in the OP. I could be wrong.

I saw the term "fixed appliance" and associated that language with service calcs since he already specified 4- 40 amp circuits. Of course I could be wrong.

 

[kwired]

Not that it necessarily makes a huge difference but if 40 amp circuit is required chances are the load is anywhere between 36 and 40.

If continuous load factor must apply then 40 amp circuit could be 29 to32 amps.