Wow...how big is this house? Whats going on in this new kitchen that makes you think you need such a large service? The last few times I did large services like that I just needed more breaker spaces.
Now they're making larger breaker panels (more spaces) for 200amp services.

"Not many utility companies will do 300A services, some like Phoenix will allow a 320A service, but MOST will do a MINIMUM 400A 3-phase service. I have never seen a 400A single phase, not even sure if they are made. "

While a true 300A residential single phase service is pretty uncommon, a 320/400A residential service is VERY common lately. They use a typical plug-in style meter and are rated 320 continuous, just like a 200A service is rated 160A continuous. Three-phase residential services are extremely rare.
I KNOW NY Is not alone in this. We get questions about 320/400A services all the time on most of the boards I go to.
With all the min-mansions you have in AZ I am surprised most of them do not have 320/400A services. Most around here do.

sunnyflies, it is highly unlikely that you need an upgrade. About the only thing that would force you into this would be a big tankless water heater. I have done many homes with geothermal units and most were 200A services.
You will most likely need a sub-panel though, just for breaker space.

In Missouri we do 400A single phase services all of the time on new construction and upgrades. If I was going up from 200 I wouldn't go anywhere except 400. I don't think there is a choice here with the utilities I have knowledge of other than 100,200 or 400amp. I do not think there would be a big difference in price between 300-400 if you are already there doing it.

Huh? 400 A 120/240 single phase service is pretty much standard around here now. What are you heating with now? If it's gas you may be right. However, if you're replacing an existing air-to-air heat pump, the energy requirements will go down. I've got 400A service, ground sourced heat pumps, and an 80KVA generator.

Eaton is one supplier.

Here is a link that might be useful: house panel - class 320 - 300 & 400 amp

Your electrician can do a load calculation for you to determine the load on your service. If an upgrade is required you will need to go to a 400amp service.I would recommend a combo meter disconnect with 2-200 amp breakers feeding 2-200 amp panels.

Petey_racer, I sure hope you are right: "sunnyflies, it is highly unlikely that you need an upgrade. About the only thing that would force you into this would be a big tankless water heater. I have done many homes with geothermal units and most were 200A services.
You will most likely need a sub-panel though, just for breaker space."

Honestly, I think quite a few places on Long Island, NY, have far bigger services than my 200 amp. I saw a pair of 200 amp boxes in the basement of a five bedroom five bath spec house that's for sale, and which I walked through out of curiosity not long ago. By the time you add in all the amenities some people want - a/c, pool, spa tubs, electric mats under bathroom tiles for radiant heat, powerful appliances, outdoor lighting, etc., I can't imagine them fitting into a 200 amp breaker box.

Our 200 amp service was put in 25 years ago for our modest 2400 sq ft house with the thought that it would be plenty (no pool, spas or high end anything). But, now that's not necessarily so, according to the HVAC person I am working with, as he adds up what will be going in. I am getting rid of an oil furnace and an oil fired hot water heater and replacing them with a geothermal system with a desuperheater and buffer tank to help preheat our water, and an electric hot water heater. We are going with electric as we are putting in solar voltaic panels to offset our homes electric usage and I want to get rid of fossil fuels. No more oil bills! YAY!

I had always understood that a 200 amp service would be fine for geothermal, and it may be in most cases, but I want to add some rooms onto the house, plus put in a new kitchen with a few high end appliances I've never been able to have before and each will require its own circuit. The geo unit alone requires 60 amps, I believe. The electric water heater will need 30 amps, the range top and its exhaust fan will need separate circuits of 15 amps each - so 30 amps for them, and refrigerator will need its own circuit too. So does the dishwasher. Something needs 40 amps - can't remember what at this hour - plus, there is the rest of the electrical wiring. I'm not planning a pool. Oh, I should add, we have a well with a 1 HP pump. That must need a lot.

I sure hope it can all fit, but at this point, I am not banking on it. My wonderful electrician of 30 years just retired at 82 and I am looking for another I can trust as much as I could him. So far, no one has come close.

Well, this is a differrent story. If you are going with back-up electric heat you may very well need an upgrade. I am not at all familiar with solar but you cannot bank on it being there when you need it. You need to be independent of it for those times.

"No more oil bills! YAY! "

I find this kind of funny. How much cash are you laying out for this new system, and how much electricity will it use when the solar is not available??? Have you calculated the payback period?? I know geothermal systems are NOT cheap!

How much cash are you laying out for this new system, and how much electricity will it use when the solar is not available??? Have you calculated the payback period?? I know geothermal systems are NOT cheap!

I was kind of wondering that myself. First off we need to upgrade the electrical service to support the new heating system. Maybe it's me but that sounds counter intuitive.

Off on a bit of a tangent I was watching some TV home improvement show touting the "green" materials they were using in their project McMansion, recycled this and environmentally responsible that. I couldn't help but think that perhaps if the house was a little smaller, they'd need a few less trees to build it and a lot less electricity to cool it. But they did use recycled blue jeans to insulate it so I guess that's what they mean by reducing the carbon footprint. :-)

Do not confuse the OCD spec'd for the units with their actual power consumption. Takes a little deeper reading of the manuals to figure that out.

Thank you ronnatalie. I will do that.

I've wanted a geo thermal system for over 25 years. Yes, its expensive upfront - I hesitated long over that, but thanks to the new Federal Tax Credit of 30% which is making it possible for me (Thank you Pres. Obama), plus a thousand back from my local utility company, its ROI through fuel savings looks to be about seven years. If I replaced my conventional system with another one and added a/c, which I do not have now, it would cost me a bundle too - I got estimates on several before making my decision. But, and this is the important factor - I would never get my money back because I would keep paying for oil or gas to run it even if I bought the most efficient system available. Nothing is as efficient as geothermal. It does run on electricity, but it doesn't take much to keep it humming.

Yes, the solar voltaic panels are also expensive, and I thought long and hard about them too, but between NY state giving a tax credit, the federal government giving one and my local utility offering a generous rebate, I can just swing it, though it's going to be tight. The pay back on it will be about six years. After that, the majority of my annual power use will be covered by what is generated. I know others who are putting it in too, for the same reasons. The lady who cuts my hair and her husband put one in several years ago and love theirs. They have only four years to go before their power is free. Meanwhile, they love the days their meter runs backwards.

I can say with confidence that the tax credits are putting a lot of people to work in the geo and solar fields. Installers from both are doing good business around here and are actively hiring, which is nice to see.

As this is our forever home, I decided it's time to make it more up to date and functional. We've been making do with one bathroom for four people, a 6' x
9' kitchen and no closets as antique homes never had bathrooms or closets. The addition will allow me to put in two bathrooms and a downstairs bedroom for us as we age - and closets, finally. What I'm doing is not extravagant. No home theaters, no big garage, no pool. I will be putting in a foundation, shelling it in, then finishing it as we can.

I spent today insulating part of what will be our new kitchen one day. I'm itching from fiberglass bits. You can bet that when the addition is uo and ready to be insulated - by me - I will be using ... denim. It's treated with boric acid so that it's fire resistant, bugs won't live in it and mice won't either. Which is a lot more than I can say for the dirty old fiberglass and rock wool insulation I have been pulling out. Yuck.

Denim gives you better sound insulation as well.

Did I read that right....you're on Long Island?...May I ask what part?

We have done a couple of 320 amp services recently on McMansions. 300 is uncommon, 320 is common. What you need to do is check with your PUCO to see if you have the service entance, (wires from the pole) to handle the upgrade. Sometimes the PUCO requires a new transformer.

I just upg mine to a single phase 400 amp service and it had to go to a CT then a 400 amp disco then to 2 200amp panels