[aimee0426]

We are having a home built and are anticipating having the following right now:

1250 square feet of living space
C/A
Fridge
Separate freezer
Washer/dryer
Over/range
Microwave
Electric tankless hot water heater

In the future the basement will be finished and add 400 square feet of living space.

Is a 100 amp service enough to cover the above or should we just go with the 200 amp service?

[stanfortyman]

TANKLESS water heater?? And you are even considering a 100A?? Forget it!

Did your electrician do a load calculation? You had better hope that 200A will be enough.
What size is the tankless unit?


There is NO WAY I'd install a 100A service in a brand new home today. I don't care how light the load is.

[aimee0426]

What is your reasoning for not doing 100amp? If we went without the tankless is there a need for more than 100amp? I'm just trying to justify the upgrade as the builder keeps telling us that we don't need it.

[aimee0426]

TANKLESS water heater??? And you are even considering a 100A???? Forget it!

Did your electrician do a load calculation? You had better hope that 200A will be enough.
What size is the tankless unit?


There is NO WAY I'd install a 100A service in a brand new home today. I don't care how light the load is.

What is your reasoning for not doing 100amp? If we went without the tankless is there a need for more than 100amp? I'm just trying to justify the upgrade as the builder keeps telling us that we don't need it.

[Washington1]

What is your reasoning for not doing 100amp? If we went without the tankless is there a need for more than 100amp? I'm just trying to justify the upgrade as the builder keeps telling us that we don't need it.

With today's demanding loads, a 100A service is not logical. A good electrical contractor will think ahead--saving you money in the coming future. Also, many home buyers are looking for a house with 200 amps or more. Reason: A. Electric cooking units B. Electric furnace C. Hot Tub (#1 around here) D. Shop E. and the list goes on...
Simple answer: Future Demand


Also, who is your builder to tell you what you do and don't need. Who qualified him or her to make this call?

[aimee0426]

With today's demanding loads, a 100A service is not logical. A good electrical contractor will think ahead--saving you money in the coming future. Also, many home buyers are looking for a house with 200 amps or more. Reason: A. Electric cooking units B. Electric furnace C. Hot Tub (#1 around here) D. Shop E. and the list goes on...............


Also, who is your builder to tell you what you do and don't need. Who qualified him or her to make this call?

I agree, I thought that going with the 200amp service was the better idea, but the builder said that in that size home you would never need more than 100 because, in his words, "you would never have everything on all at once anyways" I was also told by the father in law that even with the electric oven/stove, washer/dryer, AC, and hot water heater that we wouldn't draw over 80-90 amps... I don't know anything about it and so am pressed to find some evidence as to why it is needed

[tkrussell]

How about doing a service entrance rating load calculation, as required by NEC Article 220?

This will elminate any guessing and opinions of service size.

The electrician responsible doing the service is responsible for performing the calcs.

I like the permit forms that show the calculations done, to prove to the inspector the service is sized properly, or at least documented, and who will be liable if not.

You will be amazed as to how many electricians do not know the proper method of sizing a service, and use all kinds of "rules of thumb".

[aimee0426]

How about doing a service entrance rating load calculation, as required by NEC Article 220?

This will elminate any guessing and opinions of service size.

The electrician responsible doing the service is responsible for performing the calcs.

I like the permit forms that show the calculations done, to prove to the inspector the service is sized properly, or at least documented, and who will be liable if not.

You will be amazed as to how many electricians do not know the proper method of sizing a service, and use all kinds of "rules of thumb".

I will ask for this but the problem is that the contract needs to be worked out now, i.e. we need to decide between 100 and 200, and the house isn't even being started for a few months which means the electrician isn't even in the picture yet. Other than this option is there a way to figure it out before hand? Or would it be wise to insert into the contract that the decision will be made upon the load calculation?

[tkrussell]

There must be plans and specs, an electrician should know how to do this. If you have not hired a contractor, the designer of the plans should be able to provide load data and/or load calcs.

This is such an important issue, and everyone just igonres it doing the proper method, when it comes to homes.

Like I said with "rules of thumb", most homes only need 100 amp service,there are load reasons a 200 amp is needed.

This tankless water heater is a wild card. They need huge amounts of power, many needing 100 amps alone. Add the other loads, and many times, as Stan mentions, a 200 amp is not large enough.

Article 220 takes into consideration :

builder said that in that size home you would never need more than 100 because, in his words, "you would never have everything on all at once anyways"

But we like to be a bit more scientific than that.

Have him take on the responsibility and liability of sizing your service, see if he signs onto that. My guess is no way.

Seems some contigencies need to be included in this contract to cover yourself.

[Washington1]

I agree with TK as well!

To add: Many electricians working in the field are not responsible for doing DLC's. It's the EC that is responsible for doing the DLC.
Note: This doesn't apply to all electricians, but in a typical shop of 2 or more residential electricians (Not including the owner). They have specific people doing the estimates---which in most cases involve DLC's.

But, this does not deplete the fact that an electrician should be responsible, and educate him or herself beyond test time in our evolving trade.

[aimee0426]

I agree with TK as well!!

To add: Many electricians working in the field are not responsible for doing DLC's. It's the EC that is responsible for doing the DLC.
Note: This doesn't apply to all electricians, but in a typical shop of 2 or more residential electricians (Not including the owner). They have specific people doing the estimates---which in most cases involve DLC’s.

But, this does not deplete the fact that an electrician should be responsible, and educate him or herself beyond test time in our evolving trade.

So the contractor came back with: "Yes......100 AMPS is adequate"

So I then asked to see the calculations and he came back with: "I don't get a formal analysis.....I ask and trust my electrician to install the correct equipment just like my HVAC contractor does a heat load study but I don't normally ask for it.

If you are concerned for future use like a swimming pool, etc you can upgrade to 200 AMP for a modest fee."

Does this seem like the calculations weren't actually done? Or just that they don't ever care to ask for them?

[Washington1]

So the contractor came back with: "Yes......100 AMPS is adequate"

so I then asked to see the calculations and he came back with: "I don't get a formal analysis.....I ask and trust my electrician to install the correct equipment just like my HVAC contractor does a heat load study but I don't normally ask for it.

If you are concerned for future use like a swimming pool, etc you can upgrade to 200 AMP for a modest fee."

Does this seem like the calculations weren't actually done? or just that they don't ever care to ask for them?

My questions:

-Size of tankless
-Gas or Electric appliances
-Overhead, or underground service

[aimee0426]

My questions:

-Size of tankless
-Gas or Electric appliances

All appliances are electric (washer/dryer, dishwasher, range, microwave, freezer in garage, garbage disposal). We are not 100% positive we're going with the tankless so we aren't sure what size. Obvisouly that makes a big difference, but I didn't want to not mention it and then end up going with too little.

So I guess I would need two estimates one with electric tankless (enough for 1200 square feet, 2 baths, 2 people using it)

And the other with a traditional electric hot water heater.

[Washington1]

By the way, if the EC plans to work on your project, and the EC doesn't want to give you information on how they came-up with the service size, then I would hesitate on the answers the EC is giving.

If the EC you spoke with is guaranteed to do the electrical work, then ask him to submit how he came-up with a 100A service. I see no reason why the EC wouldn't do this. Tell him you aren't asking for unit prices for materials, you are asking for a "demand load calculation".

[stanfortyman]

So the contractor came back with: "Yes......100 AMPS is adequate"

so I then asked to see the calculations and he came back with: "I don't get a formal analysis.....I ask and trust my electrician to install the correct equipment just like my HVAC contractor does a heat load study but I don't normally ask for it.

If you are concerned for future use like a swimming pool, etc you can upgrade to 200 AMP for a modest fee."

Does this seem like the calculations weren't actually done? or just that they don't ever care to ask for them?

I am very curious that ANY electrician in today's world would even consider a 100A service on a new home. ESPECIALLY one over 1200 sq/ft, with plans to go over 1600 sq/ft. This just makes no sense to me. I don't care if the DLC came in at 60 or 70 amps.
I guarantee you, the DLC for this house HAS to be damn near 100A. WHY would you cut it so close and not allow for any future loads like A/C??

In a situation like this the line "100A is adequate, but we can do 200A for a modest extra fee" is foolish. Start at 200A and be done with it. You WILL NOT feel the cost difference in the scope of a new house, I promise you.

[Washington1]

Again, stan is correct!

[Tev]

Let's take a quick look.

De-rated general lighting and receptacle load at a minimum is 5758VA (could be more)
Dryer 5500VA (could be more)
Range 7500VA (could be more)

So far we're at 18,758VA or 78 amps.

My numbers are pretty realistic estimates and don't take every load into account, most noticeably I left out heat/air and hot water plus a host of possible fixed appliances. Any combination of those things could potentially push you over 100 amps at any given time.

I seriously would not let the contractor put a 100 amp service in that house. In fact, I think I'd find a new contractor. Maybe one that is interested in giving me what I want instead of what he thinks I need.

[aimee0426]

Thanks everyone for all of your help, I now feel quite a bit more confident about pushing for what I want.