36kw tankless water heater

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AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
Customers Upgrading to a 400 amp service to Install a 36kw Tankless unite and feed a work shop. It will be a 400 meter with 2-200 amp breakers feeding shop and house. I was thinking of Coming off the 200 amp that feeds the buss with a main lug kit. Then feed a 200 amp panel next to the tankless dedicated to it. Using the Optional method I get 138amp. so I could come off the house.
I don't feel comfortable with the deducts that it allows for the Tankless. He is using it to fill a 88 gallon claw tub. That takes a while to fill and some one could be doing clothes and cooking and trips the breaker. I was thinking of coming off the Shops 200 amp. I don't think to many people would be welding out side and using compressor and hot water at the same time but then again it can happen.
I don't really want to split them up between both 200 amps.
This is the first tankless I have done any thoughts?
 
36kw at 240v is 150a. That's almost all a 200a supply can handle continuously (160a), which water heaters are considered.

I definitely would not attempt to place this on a 200a panel supplying anything else, so the shop panel is the lesser of evils.
 
AC\DC said:
Customers Upgrading to a 400 amp service to Install a 36kw Tankless unite and feed a work shop. It will be a 400 meter with 2-200 amp breakers feeding shop and house. I was thinking of Coming off the 200 amp that feeds the buss with a main lug kit. Then feed a 200 amp panel next to the tankless dedicated to it. Using the Optional method I get 138amp. so I could come off the house.
I don't feel comfortable with the deducts that it allows for the Tankless. He is using it to fill a 88 gallon claw tub. That takes a while to fill and some one could be doing clothes and cooking and trips the breaker. I was thinking of coming off the Shops 200 amp. I don't think to many people would be welding out side and using compressor and hot water at the same time but then again it can happen.
I don't really want to split them up between both 200 amps.
This is the first tankless I have done any thoughts?
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Make sure the power utility co is aware of your plans. They are not very fond of electric tank h20 heaters here.
 
You mean "tankless", right?

FWIW, unlike storage type heaters, which can run continuously for as much as an hour while recovering from heavy use, a tankless will only draw power while water is being used and the actual current drawn will depend on the flow rate demanded. But the code does not appear to make a distinction when adding a special case to the code definition of continuous load.
 
I agree the tankless does not meet the requirements for 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...
 
A case of where 200 plus 200 doesn't exactly equal 400. I think you need a 400 amp main instead of 2-200's and you likely never trip it, with 2-200's you may not trip but probably are coming close at times.

Another option is three mains, with multiple mains you only need the supply conductor sized per load calculation even if the total overcurrent devices adds up to more.

Problem is the meter with 2-200 amp mains is likely more attractive because is probably less than many of your other options.
 
kwired said:
A case of where 200 plus 200 doesn't exactly equal 400. I think you need a 400 amp main instead of 2-200's and you likely never trip it, with 2-200's you may not trip but probably are coming close at times.

Another option is three mains, with multiple mains you only need the supply conductor sized per load calculation even if the total overcurrent devices adds up to more.

Problem is the meter with 2-200 amp mains is likely more attractive because is probably less than many of your other options.
Click to expand...

I agree with all of what Kwired said.

If the customer is absolutely determined to go electric tankless, and not propane/gas, I'd be inclined to install 3 service disconnects.
 
BTW, it may be worthwhile telling your customer that many people are unhappy with the electric tankless heater. The recovery is not a quick as the gas but gas efficient is only at 85% or so. Electric is 98% efficient
 
Dennis Alwon said:
BTW, it may be worthwhile telling your customer that many people are unhappy with the electric tankless heater. The recovery is not a quick as the gas but gas efficient is only at 85% or so. Electric is 98% efficient
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Electric is 100% efficient. That don't mean it cost less, it just means all the energy involved is transferred to the water and none is lost out through a flue.

I guess any line losses would lessen efficiency, but unless you grossly undersize conductors they will be mostly negligible.
 
Recovery rate is a concept specific to storage type water heaters. The metric for tankless would be the degree-gallons per minute heating rate

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Thanks guys. I was trying the cheapest way first but did not sit well with me. So I have never tapped the Service-Entrance Conductors before. So if I understand correctly I would follow 239.46 and corresponding sections it refers to. Then the tap conductors would be sized off the calculated load per 230.42.
So going from 400amp meter to a gutter than drop down to three 200 amp disconnects. All would be grouped together next to the meter.

“Never mind on the following questions, thought threw it and got my answer”
 
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AC\DC said:
This customer is wanting this and little 120v tankless for his bathroom sinks. Told him for a 1300 square foot house it’s overkill
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it is overkill. I don't know exactly what your heating season conditions are like, but if there is any significance to them at all it will take a long time to recover the energy saved by this water heating system vs the additional installation cost compared to a simple 40-80 gallon conventional storage tank type heater. Yes that tank type heater will lose some energy during periods of non hot water usage, but during heating season that heat is lost to the home and lessens the load on your heating system. It is an additional burden on the cooling system though, so if you have a much longer cooling season that might deserve a little consideration but probably not too much unless you are in the deep south or southwest.
 
Have another question(Sorry if its a Dumb question). It's pertaining to this job so I don't want to make a new post. According to 376.56(B)(1) Distribution blocks shall be marked "Suitable for use on the line side of service Equipment" or equivalent.

So when working on my bid last night, I could not find a Block that had that marking. Called my supply house and then NSI and they kind of did not know what I wanted.
The block I wanted has an SCCR rating, would that qualify as "Equivalent" According to 376.56.(B)(1) (I don't think it would)
Tried doing a General look around google but no luck.

Attached is the Block I was looking at http://www.nsiindustries.com/catalog...locks/al-r2-m4
 
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