100Amp enough for a 750sqf 2/1 unit?

Question

I' m planning on renovating a 2x 2/1 duplex (ca 1500 sqf total). Current electricity supply is 100Amps for each unit. My GC claims this is plenty of power since hot water and furnace both run on natural gas. I was considering upping the power supply to 150 or 200Amp for each unit on the assumption that demand for electricity will only increase over time.

Who is right? Should I leave "good enough" alone or is it worth paying now to avoid potential shortfalls in the future?

Who is right?  Should I leave "good enough" alone or is it worth paying now to avoid potential shortfalls in the future?

Jon Holdman · Answer

Actually, codes have a formula for sorting this out.  The total service size isn't the total of all loads in the house.  Its usually less than that.

So, add all those up, divide by 240 and you get your amp rating.

That said, you usually don't have to upgrade unless you're doing major work.

If you're doing any rehabbing, a copy of the code for your area is a very handy book.

John Snow · Answer

100 amps is plenty large enough. There are calcs. you can do for it but I won't bore you with them. Between the facts that you have gas in the home and products are becoming more efficient it will be fine, unless someone is really doing something unorthodox...By the way, I started out for the first 18 years as an electrician/ electrical contractor.

Andrew S. · Answer

Thanks everyone - as usual, a ton of helpful information!

I tend to overdesign things, so it's good to have some more reality-based pints of view :-)

Marc Ramsay · Answer

I had 100A on a 3200 SF house with no issues until I put in the hot tub. Even then I never maxed it out. For 750 SF with gas heat and water you will be more than fine.

I only upped it to 200A once I built my workshop and ran a 100A sub-panel to it.

As Tim Allen would say... 'More Power!!!'

Jacob Coates · Answer

See how many amps the outlets pull, and any other electrical fixture the house pulls, then add them up.

John Adamkewitz · Answer

100 amp service could come up short, if a garage is involved. With window A/C, I expect a 30 amp draw at start w/anything over 15000 btu.

Otherwise agree with @Bryan L.

John

Joshua D. · Answer

well I may not be the best object lesson here but, I currently run my whole duplex 2/1 and a 1/1 on a 100 amp and the other 100 amp from the outlet goes to a 3/2 SFR run next door.  Never had a problem with any usage...

With that said I am now adding the 3/2 with its own service, and splitting the 2 100 amp between the duplex like it was suppose to be,  but only cuz I want them all to be separately metered not because of power issues.

Take that for what it's worth..... Not much I think

Edward Burns · Answer

With the exception of kitchen appliances (microwaves, coffee makers, etc.) and some bathroom appliances (hair dryers), a lot of electrical apparatus have gotten much more efficient.  LED/LCD TV's use less electricity than there old CRT counterparts.  LED/CFL and even Halogen light bulbs are more efficient than incandescent lighting.  (note: Light color affects the apparent light quality from LED significantly IMO and halogen bulbs do create a significant amounts of heat).  Even window air conditioners have gotten better.  So with the heat and hot water being gas, I would not change it.  The exception might be for insurance purposes.  Some insurance companies are now refusing to insure properties with less than 150 amp service.

Bryan L. · Answer

I would leave good enough alone, especially with the gas heat and water heater.

100Amp enough for a 750sqf 2/1 unit?

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