120v gas tankless water heater

olly

Senior Member
Location
Berthoud, Colorado
Occupation
Master Electrician
I believe these don't have to be on its own circuit, but can someone point me to the code section that applies to these appliances? I cannot seem to find it
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
There is no code section for a tankless gas water heater. There is also no need for a separate circuit, unless the manufacturer calls for one. We have never installed one on its own circuit. The 120v is for controls and a very small pump.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
There is no code section for a tankless gas water heater. There is also no need for a separate circuit, unless the manufacturer calls for one. We have never installed one on its own circuit. The 120v is for controls and a very small pump.
Unless you have a circulating hot water system, why would you need a pump?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Unless you have a circulating hot water system, why would you need a pump?
It might simply be a misunderstanding. Most if not all the gas tankless these days used forced air combustion. So before the burner comes on the fan starts up and an airflow switch enables the burner. On mine the fan is variable speed and also runs at very high speed when the burner turns off to cool the burner area since the water is shut off.
That is why mine needs more AC power than a small control transformer and valve would draw.
 

kwired

Electron manager
Location
NE Nebraska
It might simply be a misunderstanding. Most if not all the gas tankless these days used forced air combustion. So before the burner comes on the fan starts up and an airflow switch enables the burner. On mine the fan is variable speed and also runs at very high speed when the burner turns off to cool the burner area since the water is shut off.
That is why mine needs more AC power than a small control transformer and valve would draw.
That is a combustion blower though and not a pump.

Pump would likely be for a circulating system, and usually is not an integral part of the water heater either.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
We can fuss about this blower/pump etc all day but there are some units (page 54) that have pumps for recirculating. That is not important---what is important is that the unit draws very little and is not required unless the instructions call for one.

Guidelines 3.11 Connect the Power Supply Post-Power Supply Connection Checklist
When connecting the power supply, follow these guidelines: •
Do not rely on the gas or water piping to ground the water heater.
Ground locations are provided inside the water heater. •
The water heater requires 120 VAC, 60 Hz power from a properly grounded circuit. •
If using the 5 ft (1.5 m) power cord (supplied with internal/indoor water heaters), plug it into a standard 3 prong 120 VAC, 60 Hz properly grounded wall outlet. •
On external (outdoor) models, a disconnect switch must be provided and installed for the incoming 120 VAC power. The switch should be a type that is suitable for outdoor use. Check the National Electrical Code, ANSI/NFPA 70 and your local codes for a proper switch type to use in your area. Power connections must be protected from the weather and flexible cords must use an appropriate strain relief. •
The wiring diagram is located on the inside of the water heater front cover.
 

kwired

Electron manager
Location
NE Nebraska
Seems that circulating pump would go against some the concept for having a tankless water heater, which is sort of to prevent standby losses from the tank. If you put a circulation system then you increase losses in the water piping system during standby. Or does this pump on these tankless units have some other purpose?
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Some tankless water heaters are designed to be used for hot tap water or space heating.

I suppose continuously circulating hot tap water would defeat saving standby losses; maybe there is a way to make this circulation 'on demand'.

Jon
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
We can fuss about this blower/pump etc all day but there are some units (page 54) that have pumps for recirculating. That is not important---what is important is that the unit draws very little and is not required unless the instructions call for one.
Sorry if my question was seen as adversarial. It was a genuine "I don't know" sort of thing.
 

rnatalie

Senior Member
Location
Catawba, NC
Occupation
Retired Electrical Engineer
Seems that circulating pump would go against some the concept for having a tankless water heater, which is sort of to prevent standby losses from the tank. If you put a circulation system then you increase losses in the water piping system during standby. Or does this pump on these tankless units have some other purpose?
It wastes a little energy, but it still is a win over tanked heaters. The thing circulates the water and only comes on briefly to reheat the water when it gets too cold. The Rinnai controller has a timer so you can set the hours you want to have the recirculator run.

In my case, in the summer time,it also has the effect of running the water through the heat pump's desuperheater scavenging some waste energy.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
It wastes a little energy, but it still is a win over tanked heaters. The thing circulates the water and only comes on briefly to reheat the water when it gets too cold. The Rinnai controller has a timer so you can set the hours you want to have the recirculator run.

In my case, in the summer time,it also has the effect of running the water through the heat pump's desuperheater scavenging some waste energy.
Very clever. Did you nod this up yourself, or have a really smart contractor?
 

Coppersmith

Senior Member
Location
Tampa, FL, USA
Occupation
Electrical Contractor
A tankless water heater would not work for me. I take very hot showers and use massive quantities of water doing so. I would need at least four residential-sized units to keep up. I'm not very energy efficient, but my shower is the best part of my day. (And I think I'm worth it :) )
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
A tankless water heater would not work for me. I take very hot showers and use massive quantities of water doing so. I would need at least four residential-sized units to keep up. I'm not very energy efficient, but my shower is the best part of my day. (And I think I'm worth it :) )
If you're running a normal-flow shower, the (gas) tankless will easily keep up, as long as your water isn't getting piped off a glacier. It doesn't care how long you run the shower, just the total flow rate. They are usually sized by the description of how many loads you want to run at once. Shower only, shower + dishwasher, 2 showers, etc. If you exceed the rated draw, your water just gets less and less hot proportional to the excess of the tankless' rating. They are also rated for a maximum rise over incoming water temperature, so the hottest hot depends on that.
 

Frank DuVal

Senior Member
Location
Fredericksburg, VA 21 Hours from Winged Horses wi
Occupation
Electrical Contractor, Electrical Engineer
A tankless water heater would not work for me. I take very hot showers and use massive quantities of water doing so. I would need at least four residential-sized units to keep up. I'm not very energy efficient, but my shower is the best part of my day. (And I think I'm worth it :) )
Au Contraire. A tankless is perfect for that use. Well, as long as you have gas (natural or LP available). I have no experience with electric tankless. Just get the largest burner available, for residential that is 199,000 BTU. My 15 year old Noritz has a 199,000 BTU burner and the controls go to 160° F. That's enough BTUs to heat 55° F water to 120° F at a low rate of 6 gallons a minute. Or 7.5 GPM if only heating 55° F water to 110° F. Of course, there are instructions for commercial use where you use two or more tankless for hotels, laundromats, etc. Or, you can get a commercial 380,000 BTU model!!!!

And Tampa has what temperature water entering the home? I bet it is over 55° F!

If you are mixing your shower water to over 105°, you are a lobster. ;)

The downside is not what you think, it is: no reason to leave the shower until you run out of water or gas!(y)
 
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