When tankless water heater is used instead of tank water heater (27000 or 36000va vs tank 4500va) how should the calculations be done to size the panel in a dwelling unit, are tankless water heaters addressed in the code for residential load calculations?
Instant Water Heaters Residential Calculation.
- Thread starter Bernardoc
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cadpoint
Senior Member
- Location
- Durham, NC
Your under ICC bldg code, in researching your desired answer your tankless is suppose to have an output of 2 GPM per sink(think drain)
I can't re-find that link.
If your saying your tankless is at 4500vA, Article 422.11(F)(3), and or Article 422.13 in NFPA 70.
florida bldg building code for tankless heater
The existing Panel size is > ?
I can't re-find that link.
If your saying your tankless is at 4500vA, Article 422.11(F)(3), and or Article 422.13 in NFPA 70.
florida bldg building code for tankless heater
The existing Panel size is > ?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
He's comparing a 4500 watt tank style to a larger tankless.
cadpoint
Senior Member
- Location
- Durham, NC
The Articles still apply. If the Designer wants to put up to 120 Amp DPB on a panel .
Yeah I'd Say they need to do a calculation.
Yeah I'd Say they need to do a calculation.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The question is how did a tankless water heater get added to a load calculation? Is it at 100% or can a demand factor be used?
cadpoint
Senior Member
- Location
- Durham, NC
It's not clear to me, why don't you answer the gentleman, you've been clear of my mis attempts to help.
The first four Articles are for Electrical installations. There's no examples of adding this bohemias in Annex D for Single
Family dwelling as I reviewed it, If I miss it, pardon me. I can understand the OP problem.
There's nothing in my Listed Articles that qualify it nor how to use a load calc. nor a determination of anything less than a 100%.
as it's applied to what's shown in Annex D.
Or perhaps that is why we're all here to feed the Mike Holt Code Submittal Machine.
The first four Articles are for Electrical installations. There's no examples of adding this bohemias in Annex D for Single
Family dwelling as I reviewed it, If I miss it, pardon me. I can understand the OP problem.
There's nothing in my Listed Articles that qualify it nor how to use a load calc. nor a determination of anything less than a 100%.
as it's applied to what's shown in Annex D.
Or perhaps that is why we're all here to feed the Mike Holt Code Submittal Machine.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Only postive thing about an electric tankless is you don't have to add for a continuous load. A whole house electric tankless will most certainly increase the service size from what it would normally be. Most will require (3) 40A circuits for one large enough for a whole house.
@Bernardoc
It would be much better if you can talk your clients into a gas tankless. Less electrical load and better recovery time for hot water.
@Bernardoc
It would be much better if you can talk your clients into a gas tankless. Less electrical load and better recovery time for hot water.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The problem is that the NEC does not give us any help but imo, since the nec does not require it to be at 100% then it can be listed as one of the appliance and treated that way. 4 appliance and then 75%
- Location
- New Jersey
- Occupation
- Journeyman Electrician
That's was my thought as well but I wasn't sure if the 4 appliance rule would apply. As you've pointed out it is not spelled out in Article 220.
Tulsa Electrician
Senior Member
- Location
- Tulsa
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- Electrician
I did find this.
iaeimagazine.org
Go Tankless…and Stay in Hot Water
iaeimagazine.org
Attachments
yes, that is the question, when this type of water heater is use, they have 3 40 amp breaker, and two shower will bring it to a full load.
If we use a demand factor what it will be. I dont think that the NEC is addressing the Instant water heater correctly.
I am more incline to applied a demand factor of 75%. In the panel it is the biggest load and it will go full power when two showers are use.
This is new construction, for one bed room and two bedroom apartments 500sq ft for one bed room and 800 sq ft for two bed room. For one bed room the total load is 34280 VA including the 10.8 kw instant water heater. If I apply the standard calculation the first 10kw at 100% the rest at 40% we will have 19712 VA. At full load the water heater will take 10800 VA so I have 10000VA for the rest of the appliances, excluding the AC. I think I am to close to trip the breaker, the instant water heater will demand a full load when in use. In my opinion I will take the Instant water heater an apply a 75 % demand load so it is more realistic load. Does anybody have a different opinion.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
The point of demand factors is that load diversity allows lower total demand than the sum of the individual demands. In other words: not everything will be on full blast all at once.
In the situation you describe, you have one 'dominant load', so I don't see much opportunity for diversity.
Now the load itself modulates, when the incoming water is warmer or the flow is lower, it uses less power. But 10.8 kW is barely enough for a hand washing sink, so a smaller tankless electric can be expected to run full blast on a regular basis.
On the other hand once you are talking the aggregate load of multiple individual units, people run the hot water at different times, and there will be lots of opportunity for load diversity and demand factors. But I think you are asking about the individual units.
Jon
In the situation you describe, you have one 'dominant load', so I don't see much opportunity for diversity.
Now the load itself modulates, when the incoming water is warmer or the flow is lower, it uses less power. But 10.8 kW is barely enough for a hand washing sink, so a smaller tankless electric can be expected to run full blast on a regular basis.
On the other hand once you are talking the aggregate load of multiple individual units, people run the hot water at different times, and there will be lots of opportunity for load diversity and demand factors. But I think you are asking about the individual units.
Jon
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Why does an 18KW tankless water heater present a load of 10,800W?
-Jon
-Jon
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I once did a house with 30 kw heat and it came out to 198 amps. The owner would not allow me to jump to 400 amps.
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