Sizing Water Heater

Status
Not open for further replies.

frank_n

Senior Member
Location
Central NJ
I'm sizing a 119-gal water heater with 2- 4500 watt heating elements.

2 x 4500 = 9000 watts.
9000 watts / 240 volts = 37.5 amps.

Since the water heater is considered a continuous load, 37.5 x 125% = 46.875.

I should use #6 THHN and a 40-amp breaker.

Did I do anything wrong?

Frank N.
 

Bea

Senior Member
I would agree with stickboy if the hotwater tank has a upper and lower element but the size of the tank that is list I think that may not be the case. Using your cal. you could actually use #8 THHN and put on 40 or 50 over-current device.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
iwire said:
I don't think you will see simultaneous operation of the elements until you move into commercial units.

He did not say if this is commercial or residential.119 Gal sounds rather huge for a home.Large homes might have 2 normal size 40 gal..To heat up 119 gal with only 4500 watts could take all day.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
stickboy1375 said:
The only way to be sure is too look at the unit itself... what else can I say?
Correctamundo. The label will probably read "Upper element - 4500W, Lower element - 4500W, Total - 4500W" if they don't run simultaneously.
 

iwire

Moderator
Staff member
Location
Massachusetts
Has anyone seen an electric dwelling unit water heater of any size that did not ship from the factory wired for alternate operation if it had more than one element?

I have seen people rewire them for simultaneous operation, and when the 30 amp cartridge fuses blew they wrapped them with tin foil.:mad:

Of course I should mention I was in this house after an electrical fire had caused the inspector to have the meter pulled.:grin:
 

frank_n

Senior Member
Location
Central NJ
Yes it is a commercial application. The heater is not bought yet, but I wanted to know how to size it for bidding purposes.

Frank
 

Bob NH

Senior Member
benaround said:
I'm glad it's a 119 gallon tank because a 120 gallon tank would be just crazy.

The reason for the 119 gallon tanks is that the ASME Pressure Vessel Code doesn't apply to domestic water tanks (and perhaps others) that are less than 120 gallons. That is why you see 119 gallon water heaters and 119 gallon hydropneumatic tanks.

If you need a coded pressure vessel, the cost goes way up.
 

Bob NH

Senior Member
I looked in my Grainger catalog and all of the single phase units with 4500 Watt elements operate only one element at a time.

Check the specs on the heater. If the recovery rate is given, 4500 Watts = 21 Gallons per hour at 90 degree F temperature rise.
 

kc8dxx

Senior Member
Location
Ohio
Bob NH said:
The reason for the 119 gallon tanks is that the ASME Pressure Vessel Code doesn't apply to domestic water tanks (and perhaps others) that are less than 120 gallons. That is why you see 119 gallon water heaters and 119 gallon hydropneumatic tanks.

If you need a coded pressure vessel, the cost goes way up.

Let me quantify for the casual reader what "cost goes way up" means. We have a tank in one system that is 18 gallon. Customer wanted it to be a coded pressure vessel. Cost went up by a factor of six. Customer was not happy with the price increase. :rolleyes:
 
Status
Not open for further replies.
Top