tankless water heater

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jamesjacco

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Location
ormond beach fl.
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electrician
ok there is not much info on electrical tankless water heaters in the NEC. I need clarification on how to apply this fixed appliance for load calculations. Meaning is it a continuous load or noncontinuous and where is it in the NEC as far as demand factor ? I look forward to everyones knowledge and wisdom. thank you
 
As I understand it there is no tank so it is not a continuous load.

422.13 Storage-Type Water Heaters. A fixed storage-type
water heater that has a capacity of 450 L (120 gal) or less shall
be considered a continuous load for the purposes of sizing
branch circuits.
Click to expand...
 
Unless you are taking a 3+ hour shower, I can't see a tankless water heater being a continuous load. A storage water heater is constantly losing heat to the air around it, so I can see that being a continuous load.
 
Seems like there is a time period that defines continuous and non-continuous loads. Tankless consumes more power when operating, but not the same time period as a tank type.
 
hillbilly1 said:
Seems like there is a time period that defines continuous and non-continuous loads. Tankless consumes more power when operating, but not the same time period as a tank type.
Click to expand...
It's 3 hours, but as was said, the tankless will not run continuously for 3 hours. Only storage tank type heaters are considered continuous.

If it was me, I would highly suggest to the customer to go with a gas tankless, much more efficient and doesn't require upsizing the service.
 
gadfly56 said:
Unless you are taking a 3+ hour shower, I can't see a tankless water heater being a continuous load. A storage water heater is constantly losing heat to the air around it, so I can see that being a continuous load.
Click to expand...
The heat loss is so small compared to the "loss" during water usage that 3+ hours at full power is very unlikely. Unless you are starting from turn-on with a full cold tank and using water as soon as the top layer is heated, what you will see is cycling on and off to maintain temperature.
 
Typical tank style heater probably doesn't run for 3 or more hours at a time, unless it is marginally sized for actual demand, which is plumbers fault more than the electricians if that happens.

My guess is NEC has other reasons why they decided to consider it a continuous load.
 
I do not think anyone here understands my question. ok it is a non continuous load great. what is the demand factor ? it is not a luminare. it is a fixed appliance. so would I use the first 8kva at 100% and then the remaining kva at 40 % ? this is what I remember for adding non continuous appliance loads but I cannot find it in the NEC.
 
jamesjacco said:
I do not think anyone here understands my question. ok it is a non continuous load great. what is the demand factor ? it is not a luminare. it is a fixed appliance. so would I use the first 8kva at 100% and then the remaining kva at 40 % ? this is what I remember for adding non continuous appliance loads but I cannot find it in the NEC.
Click to expand...
Only thing I am aware of that could apply is 220.53 - you need four or more appliances that are fastened in place that are not electric ranges, clothes dryers, space-heating equipment, or air-conditioning equipment and are on same feeder or service conductors and you can use 75% demand factor

220.83 has your mentioned 8kVA @ 100% and remaining at 40% - is part of optional calculations for existing dwellings, and is intended to be used to determine if you have room to add new loads
 
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