29kw electric water heater

Status
Not open for further replies.
J

jes25

Senior Member
Location
Midwest
So I have a client rewiring a house. 1600 sq ft. On demand water heater 29 kw, electric range, dryer, no AC. I came up with a laughable 115 amp service when I calculated the service using the IRC (over 10k va gets derated to 40%) Perhaps I did something wrong? Im trying to decide between a 200 amp service or twin 150s (300 amps). Any thoughts from the community? Also, a water like this wouldn't be considered continuous would it? I guess you could take a 3 hour shower.

Sent from my SM-G950U using Tapatalk
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
jes25 said:
So I have a client rewiring a house. 1600 sq ft. On demand water heater 29 kw, electric range, dryer, no AC. I came up with a laughable 115 amp service when I calculated the service using the IRC (over 10k va gets derated to 40%) Perhaps I did something wrong? Im trying to decide between a 200 amp service or twin 150s (300 amps). Any thoughts from the community? Also, a water like this wouldn't be considered continuous would it? I guess you could take a 3 hour shower.

Sent from my SM-G950U using Tapatalk
Click to expand...

I think electric heaters are required to be considered as continuous even if they are not.

What do you think is laughable about the 115 Amp service? If the calculation comes out to 115 Amps that is what it is.
 
david luchini

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
The instantaneous water heater is not a continuous load. Do the calculation with the water heater at 100% instead of including it in the 40% general load factor.and see what that gives you.
 
M

MyCleveland

Senior Member
Location
Cleveland, Ohio
No AC ?, is it gas heat or electric ?
If no AC or electric heat you cannot use optional calc,

I would go with post 3 and NOT treat this as an appliance and add in its total load.
 
J

jes25

Senior Member
Location
Midwest
It does have heat, but it is a gas furnace and thus very little electrical load. I like what others have mentioned and I'll add the water heater in at 100%.


Seems to me we have discovered a little quirk in the code.

Sent from my SM-G950U using Tapatalk
 
Strombea

Strombea

Senior Member
Location
Prescott, Arizona, USA
I install a lot of tankless electric water heaters and you absolutely have to be at 100% because the 29k rating is actually what it uses. This it WILL use is 120 amps at full water flow. Turn on the range for some cookies while wife is in the shower and your at least 140amps. 200 amp panel would be marginal.
 
R

rjniles

Member
Location
Coastal South Carolina
jes25 said:
It does have heat, but it is a gas furnace and thus very little electrical load. I like what others have mentioned and I'll add the water heater in at 100%.


Seems to me we have discovered a little quirk in the code.

Sent from my SM-G950U using Tapatalk
Click to expand...
Why would anyone install an electric instantaneous when gas is available?


Sent from my RCT6213W22 using Tapatalk
 
H

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
electrofelon said:
Why would anyone install one at all.
Click to expand...

I take it your not a fan if these.
I have never had one.
I agree with some, the all electric instantaneous will cost them a fortune in the end. I don’t believe they will ever replace it when it goes out.

My question though, what don’t you like about the gas units? My thoughts are no energy usage until called for. Not constant storage and reheating.
am I missing something?

I would like to know your opinion, I was kind of thinking about a propane unit when my 20 year old tank water heater went out.
 
mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Strombea said:
I install a lot of tankless electric water heaters and you absolutely have to be at 100% because the 29k rating is actually what it uses. This it WILL use is 120 amps at full water flow. Turn on the range for some cookies while wife is in the shower and your at least 140amps. 200 amp panel would be marginal.
Click to expand...





2585w/240v= 10.7 amps. So 130 amps worse case. People tend to over exaggerate how much residential appliances draw let alone all the load diversity involved.

What I would really be concerned about is telling the power company that a 120amp load is inside the home.



i-r36Q6Ps-X3.jpg
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Hv&Lv said:
I take it your not a fan if these.
I have never had one.
I agree with some, the all electric instantaneous will cost them a fortune in the end. I don’t believe they will ever replace it when it goes out.

My question though, what don’t you like about the gas units? My thoughts are no energy usage until called for. Not constant storage and reheating.
am I missing something?

I would like to know your opinion, I was kind of thinking about a propane unit when my 20 year old tank water heater went out.
Click to expand...

I am not a fan of on demand electric units for several reasons. Capital cost and reliability is one. Also they often seem to have problems with temperature stability. Electric tanks are completely surrounded by insulation so stand by losses are minimal (gas tank units on the other hand have lots of losses through the flue). I don't think they are worth it.
 
ActionDave

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Hv&Lv said:
I take it your not a fan if these.
I have never had one.
I agree with some, the all electric instantaneous will cost them a fortune in the end. I don’t believe they will ever replace it when it goes out.

My question though, what don’t you like about the gas units? My thoughts are no energy usage until called for. Not constant storage and reheating.
am I missing something?

I would like to know your opinion, I was kind of thinking about a propane unit when my 20 year old tank water heater went out.
Click to expand...

I'll jump in here.

They are overly complex for the job they do, they are overly expensive for the job they do and they don't last as long. Maybe your monthly gas bill will go down, but I doubt it offsets the cost of install, maintenance, and replacement.

edit to add, I'm talking about the gas units.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Strombea said:
I install a lot of tankless electric water heaters and you absolutely have to be at 100% because the 29k rating is actually what it uses. This it WILL use is 120 amps at full water flow. Turn on the range for some cookies while wife is in the shower and your at least 140amps. 200 amp panel would be marginal.
Click to expand...
Why is that marginal? You have 30% of what is designed for still available. Plus reality is that main isn't going to trip the instant current reaches 200.01 amps, it could ride through 250 or even 300 amps for short periods of time if it had to.
 
Strombea

Strombea

Senior Member
Location
Prescott, Arizona, USA
kwired said:
Why is that marginal? You have 30% of what is designed for still available. Plus reality is that main isn't going to trip the instant current reaches 200.01 amps, it could ride through 250 or even 300 amps for short periods of time if it had to.
Click to expand...

The point is that it's just 1 appliance, you are relying on 30% left but still have the rest of the home to use. I'm not a fan of these either and all I'm saying is don't weld in the garage, cook in the oven or dry your clothes, or use electric heat while your heating water (with all 3 elements on). In what other residential situation is 1 appliance using more than 50% of total service. BTW almost all the ones I have put in at this size end up dimming the lights in the house because existing POCO feeders and transformers are not sized for such a resistive load and now I have to get POCO to upgrade equipment.
 
Status
Not open for further replies.
Top