Tankless water heater

nizak

Senior Member
Customer is inquiring about having a 29KW unit installed in a residence.

Specs call for (3) x 40A Circuits.

Should the Poco be contacted before something like this is installed?

First off I need to verify customer service size.

I do know that many of the pole mounted Xfmrs around here are 25Kva.

Anybody here routinely install these types of units??

Mfgr spec states: "Dwelling must be supplied by a 200A electrical service"

Just doesn't seem practical to try to add this amount of load.

Thanks
 

tom baker

First Chief Moderator
Staff member
Yes that is a large load! I have a tankless gas its 180K BTU so endless showers. I used tankless as it was in the basement and venting would have been difficult. The disadvantage is (and let the customer know this) there is no standby loss, so the hot water cools off in the pipes and I need to run several gallons of water to get it hot. So the upstairs bath I have an electrical kettle, heat water in it for about 15 seconds to wash up with. A heat pump water heater would be the way to go
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Yes that is a large load! I have a tankless gas its 180K BTU so endless showers. I used tankless as it was in the basement and venting would have been difficult. The disadvantage is (and let the customer know this) there is no standby loss, so the hot water cools off in the pipes and I need to run several gallons of water to get it hot. So the upstairs bath I have an electrical kettle, heat water in it for about 15 seconds to wash up with. A heat pump water heater would be the way to go
They do make a circulating pump that works with tankless water heaters. I had a customer that used on with his Rinnai gas tankless.
 
Circulating pumps don't discriminate; they work equally well with tanked or tankless heaters.
If they run all the time, they provide immediate hot water, at the expense of increased energy consumption.
They can be configured to run only on demand, but user familiarity, learning curve and acceptance is problematic.
They're not terribly well suited for retrofitting an existing building because they require a return pipe.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
They're not terribly well suited for retrofitting an existing building because they require a return pipe.
There are the residential type that mounts under a sink and pushes the incoming (not-yet) hot water into the incoming cold-water pipe.
 

nizak

Senior Member
I guess my original post was directed more to the issue of :
Does the POCO need to be made aware of the installation of a high wattage draw appliance such as a tankless unit consuming 120 amps that's in a residential setting?

I think that draw would have an affect on other customers being served from the same pole mounted xfmr.
 

growler

Senior Member
Location
Atlanta,GA
Customer is inquiring about having a 29KW unit installed in a residence.

Specs call for (3) x 40A Circuits.

Should the Poco be contacted before something like this is installed?

First off I need to verify customer service size.

I do know that many of the pole mounted Xfmrs around here are 25Kva.

Anybody here routinely install these types of units??

Mfgr spec states: "Dwelling must be supplied by a 200A electrical service"

Just doesn't seem practical to try to add this amount of load.

Thanks
I like to start by asking the customer what they hope to accomplish by having this type of unit installed.
A few years ago I asked a customer and they had several multi-headed showers they hoped to use at the same time by installing a tankless unit.

Even with a monster like this it will only heat a set amount of water per minute measured in gallons.

The homeowner should really be talking to a good plumber to see if this is what they need.

If this is what they want and they have lots of money it's time to do a load calculation of the house and see if the service is big enough or if a larger service is needed.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Does the POCO need to be made aware of the installation of a high wattage draw appliance such as a tankless unit consuming 120 amps that's in a residential setting?
I'd say absolutely yes. It's better to contact them and be wrong than to not contact them and be wrong.
 

StarCat

Industrial Engineering Tech
Location
Moab, UT USA
Occupation
Brewery Engineering Plant Technician - HVACR Electrical and Mechanical Systems
Tankless water heaters are an Engineering Disaster......
 

kwired

Electron manager
Location
NE Nebraska
Unless their tariff includes a demand charge, the bill will be about the same as if a tanked water heater were installed.
Residential electric bills usually charge for energy, not power.
There should be less standby losses. How significantly less will depend on other factors. If you happen to live in colder climate and have electric heating, those losses just go to heating your place. If you live in warmer climate and run the cooling system a lot, those losses add to the cooling load.
 

Beaches EE

Senior Member
Location
NE Florida
Occupation
Electrical Engineer / Facilities Manager
Unless the customer is adamant about using an electric tankless and/or gas is not available, these units place a significant load on the service and the POCO transformer. Growler's advice about a plumber makes sense. I have read that heat pump water heaters can be a good solution.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Unless their tariff includes a demand charge, the bill will be about the same as if a tanked water heater were installed.
Residential electric bills usually charge for energy, not power.
I'm talking about an electric heater versus some other type like natural gas. Around here you would choke on the cost of running an electric water heater that large because of high electricity rates.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Our rates are pretty reasonable, a lot of hydro around here, but will probably start going up due to the amount of solar being installed. Once the subsidies run out, they will have to cover that cost.
 

kwired

Electron manager
Location
NE Nebraska
I'm talking about an electric heater versus some other type like natural gas. Around here you would choke on the cost of running an electric water heater that large because of high electricity rates.
Outside of demand charges, energy used is still going to be same as for a smaller kw tank style heater less the idle time losses, presuming you used the same amount of hot water. You just using at a higher rate when you are using, kWHrs will be similar when all is said and done.
 
There should be less standby losses. ...
Did you learn that from your dad? Put your hand on a modern foam-insulated water heater and notice that it isn't warm. Little or no temperature difference between the surface and the air means little or no heat loss.

The tank type might have an energy-bill advantage if the household has heavy users and they end their long showers because the tank runs out of hot water when the otherwise wouldn't.

When smart grids are implemented, large-tank water heaters can be used for consuming renewable energy when it's abundant and storing it for later use.
 
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