Instant Water Heaters Residential Calculation.

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Bernardoc

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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?
 
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.
 
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?
 
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.
 
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.
 
cadpoint said:
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.
Click to expand...


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%
 
Or use the optional calculation. It will most likely have a 0.4 multiplier applied to it just like everything else once you're over 10KW and it isn't HVAC. Same issue with car chargers except they run longer.
 
Dennis Alwon said:
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%
Click to expand...
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.
 
cadpoint said:
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 > ?
Click to expand...
infinity said:
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?
Click to expand...
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.
 
infinity said:
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?
Click to expand...
If we use a demand factor what it will be. I dont think that the NEC is addressing the Instant water heater correctly.
 
Dennis Alwon said:
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%
Click to expand...
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.
 
cadpoint said:
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 > ?
Click to expand...
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.
 
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
 
The information that we have from manufacture is at 240 volts, so when we have 208 the KVA is degrade by 25%, the same with the temperature rise and the amps.
 
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