HVAC (central air/heat) systems, what voltage wiring do these typically use?

I am thinking about installing a HVAC / central heating & air system in my house. I was told by an electrician who came by that I must upgrade my wiring to 220v in order to use an HVAC system… I am a bit skeptical as to whether this is really required or if I’m being sold on extra work. Was hoping anybody with insight or experience here with HVAC systems/installation could chime in.

A handyman that is helping with other work on the home advised me to have electrician come by to upgrade the fusebox to a 200amp box (currently 100amp) to accommodate an HVAC system.

I called up an electrician who came by to look things over and told me I must use 220v with an HVAC system. His description seems involve more work/costs than I imagined, including having someone from city come out fiddle with the power meter or something so I can use 220v.

I am a bit skeptical on the advice that I must have 220v wiring. I don’t see why I cannot simply use 110v wiring… I know the basics that volt*amp = energy used, and you can increase the energy supplied/used if you increase the amps.

Do residential HVAC units require 220v for operation? If not, is there a significant advantage to selecting a unit and installation that uses 220v?

General info:
Home is ~900sq ft, 8 ft high ceilings
2 bed / 2 bath
I think I need a 1.5-2 ton capacity unit (if the unit capacity matters) for my location (California)
Probably use 3 vent openings (two bedrooms and a living room)

Thanks for any help! I don’t want to be ripped off or oversold on services I don’t need. I’m hoping to do a bit of learning on the topic before trying to call another “professional” for a quote.

Yes, most central HVAC systems use 220 for the compressor.
I don’t even want to think about your current wiring if it takes a meter swap to get 220. Most residentil wiring has 3 wires coming into the meter - 2 black and a white. The voltage across 1 black and the white is 110; across the 2 blacks is 220.

2 concerns if you are thinking HVAC as a DIY:

  1. You should know the above basics re. residential wiring.
  2. You probably do not have the EPA license required to buy refrigerant, nor the tools/knowledge to install it.

You have a small house - a couple of (110 AC) window units might be enough, But, again, if you have 100 amp service, they will trip the circuit breaker/blow the fuse.

Once you get modern wiring, look into “split AC systems” - it is remotely possibe for a novice to install one in such a way as to provide sufficient cold air.

If you want to know how much tonnage you need, run a “maunal J” calculation. Finding that will lead you to a wealth of info on HVAC.

edited to fix spelling

Thanks for the quick reply about most systems using 220 volts.

I don’t plan on installing the HVAC or AC myself. Sometime in the future I was hoping to have a pro install a system.

When fixing a few things around the house, handyman suggested I call an electrician to replace my fusebox at this time (and also to upgrade it to a higher amperage unit).

When the electrician recommended a different set of services/changes, I wanted to understand a bit more what exactly was required before having service done. My goal is pretty much just to repair/replace old parts, and also to have it ready for the option of having an HVAC system installed in the future.

Thanks again.

The air conditioner will need about 30-40 amps at 240. I’ve never seen a central unit that could be run on 120.

If you’re thinking of modernizing your home’s wiring, plan on $5000 - 10,000 for the job, depending on how many new circuits you want to run. Sad to say, but copper wire is about as expensive as it’s ever been, which is to say “very” and some required wiring devices like arc-fault breakers for bedroom circuits will run about $50 each. Labor is another thing that’s always expensive.

How your house is built will affect the cost - if you have an accessible crawlspace or unfinished basement, labor will be somewhat less as new wire can be strung along easily, but a slab-on-grade foundation will involve more time to sneak new wires around, unless you go really cheap and run the new wiring around the outside of the house, which looks terrible.

The price difference between a 100 amp and a 200 amp main panel is negligible, and you’ll pat yourself on the back three years from now when you want to add some circuits for a garage workshop, or perhaps a hot tub, and there’s space in the panel just waiting to be used. I frequently curse whoever went cheap when building my house as they put a 90 amp panel into a 1500 square foot house.

It’s not feasible or sensible to keep your old fusebox and update the electrical service to support it and an air conditioner. As it’s got 100 amps worth of 120 feeding it, you’d need a 240 amp service entrance to provide that 100 amps of 120, plus the 40 amps of 240 for the AC. The equipment to provide this would probably wind up being an expensive special order instead of something that could be bought off the shelf at Home Depot.

Depending on what else you have running 100A service might be enough, but it will leave you no room for expansion.
When I added central AC for my 1400 square foot house I went from 60A service to 100A. When I added a spa, and rewired my garage I went to 200A. That cost me about $1,000.
You already have 220V at your house, the question is do you have a large enough service for all the electrical consumers you have in the house.
Unless your house is rather stupidly built I would expect the upgrade to 200A and a new circuit to the AC unit to cost under $2500. (LA prices)
Talk to a couple of contractors.
Upgrading the service requires (at least in the city of LA) a meter spot from the Department of Water and Power (free) and a permit. (not free). Basically you call the DWP they come out and tell you where they will allow you to place the new meter. ( I want it here. No. How about here? No. Here? OK fine. :))
The electrician’s work will have to be inspected (this is why you got a permit)
I hope this answers your questions. if not feel free to ask.

Wow, just wow.
I’m an electrician in the Midwest and I’ve never heard of a home electrical service that wasn’t 220 volts.
I’m guessing that there was a breakdown in communication somewhere.

Couple of points;

You probably DO have 220 coming in to the house.
If it’s a 100 amp service then you most likely need to add a subpanel to facilitate the breaker(s) needed add the AC unit. Or, you could replace the 100 amp panel with a different 100 amp panel that has more breaker spaces in it. You might have a 20 circuit panel, for instance, and you could move up to a 24 or 30 circuit panel. This could be the cheapest route.

Under no circumstance should you need to upgrade to a 200 amp panel for a 900 sq foot home. Ever. Unless you got some really fancy shit in that house. We’re talking hot tub, electric heat, AC, electric range, electric dryer, tool shop out back, a plethora of lighting, etc…
Don’t buy it. Have the electrician hook up an amp-meter to one of the lines coming into the house and show you what the current draw is under normal useage.

I’ve hooked up AC units in 1500 sq foot homes that only required a 220 volt 25 amp supply. You might only need a small unit with a 220 volt 20 amp supply to it. If one’s is available.

So, you might need a new panel or the addition of a subpanel. If you really don’t have 220 coming in, I’m at a loss. Nothing is made for a residence that would only support a 110 volt service. Panels are all designed for 220 volt and so are all the meters and meter sockets that I’ve ever seen. And the wiring in the house, if it’s only a 110 volt service, would need to be carefully redone to facilitate the addition of 220 volt wiring. This is just beyond reality. I think you need to get this clarified.

My mother’s house had a 60 amp service, with actual screw-in fuses. She had central air installed, and they must have put in a sub-panel. She sold her house a year or two ago, and it still had the screw-in fuses, so they didn’t replace her panel, just added on.

Maybe you should try calling an HVAC installer, rather than calling an electrician directly. They must run into this situation all the time, and would have electricians they use who are familiar with this sort of situation.

You shouldn’t have to replace all of the wiring in your house to upgrade service, though.

Also, you may only have to upgrade the service entrance to 200 amps, while leaving the service panel at 100 amps. Then at the service entrance, at the top of the meter, you’ll branch off to another meter. If you’re going to have pure electric HVAC, then chances are good that your utility has a separate space-heating rate that will require a second meter. Load load side of the second meter will go to another junction box and auxiliary panel without affecting your existing 100 amp distribution center.

Again, even if you upgrade the service entrance and the distribution center, you probably shouldn’t have to upgrade the rest of your wiring. Unless you have non-grounded existing wires everywhere (not sure what the NEC or your local codes will grandfather).

The down side is your utility planner may decide that the inrush current of your new compressor exceeds the existing capacity to your house! When the compressor starts, the service entrance voltage is supposed to drop no more than seven volts, otherwise you’ll cause noticable flicking in your house and your neighbors houses. I had a near miss with this when I replaced my system with a ground source heat exchanger. The utility wanted to place a huge friggin’ transformer in my yard (and not even the easement), which they’d have delivered and connected to the pole free of charge. To connect that transformer to the house, though, would have been another thousand dollars. Plus, I’d have a big ugly transformer in my back yard.

I’ll bet you’d also instruct the homeowner - to turn on as many appliances as he can when doing this…and maybe leave any refrigerator/freezer doors open.

One thing that I’m not sure was clear from other posts; besides the service panel & meter/socket, it’s conceivable the town/utility would need to run new cable from the utility pole to the meter socket. (Maybe that’s considered part of ‘service entrance’).

Our neighborhood has underground service and it involved digging to install new cables. I believe some areas now employ a buried conduit to simplify upgrade/repair and eliminate future digging (a bummer if it runs under somebody’s driveway, walk, or nice lawn.)

Ah, I missed that part. In lieu of the utility planner planting a big honkin’ transformer in the middle of my back yard, he had the company run a new line from the pole to my service entrance. I don’t remember the sizing – probably 2/0 to 1/0 or something like that – but it was completely free of charge. The utility (DTE in my case) will commit to bringing the power to your “service entrance.” As I said, the big honkin’ transformer would have been free, but it would have been the termination point for my property. I’d still be responsible for bridging it to my meter.

More specifically, the cable upgrade wasn’t all the way to the meter, but to the junction point prior to the drop, i.e., the big metal pipe that actually goes into the meter.

A friend had terrible electrical service. After a year of complaining about the power the electric company figured out the transformer on the pole only was rate for 60 amps and it supplied the neighbor and their 100 amp service too. Originally the two houses were cottages, and then they weren’t. Nobody at the power company thought to replace the pole transformer, when the lines were disconnected and the service changed. I could see something like a house with only 110 volt service in that town.

I can’t speak for the midwest, but I can definitely say that I’ve seen at least a couple of homes on Long Island, NY, that had only 120V service. We’re talking houses built in the 1950s, most likely.

I’m going to second someone else’s suggestion that you consider a ductless split system for each room rather than a central system. Only trouble is that the smallest system I’ve seen is 3/4 ton, which is probably more capacity than you need.

Split systems can be installed by someone who’s a bit handy (not “painting a room” handy, more like “replumbing a kitchen” handy). You’d have to buy some specialized tools (a vacuum pump and a set of gauges, and probably a pipe flaring set), but you can pick them up on ebay for under $300.

The advantage of the split system is that you don’t need to cool rooms you’re not using, so at night you could just cool your BR and leave the others off.

Mitsubishi’s Mr. Slim is probably the most popular of the ductless split systems, but there are many others.

No, normal conditions under normal circumstances. If you’re entertaining 30 people and you have everything in the house turned on full blast you can expect to trip breakers or blow fuses, we’re not concerned about this. Houses aren’t designed to be operated like restaurants or hotels or tool and die shops. That’s why I would turn on the appliances and lights that you would use on a typical day and start there.
Now, if you’re close to the 80 percent level (on the mains) with only the standard appliances and lights on then you’ve got to worry about doing something.
People are always surprised at how little current the home uses when they think they have a lot of stuff on. Just cause the breaker says 30 amps, or 50 amps doesn’t mean the appliance uses anywhere near that. It’s designed to be overkill anyway. A 50 amp circuit is designed to be run continuously at 80% so that would be 35 amps continuous - max. And it might only push 30+ amps for a few seconds at start-up and then coast along at 10-12 amps for the rest of the cycle. Same with AC, Range, Hot Tub, etc.

I am prepared to be corrected by someone that knows more than I do, but if you look at where the wires come down from the pole and into the house, if there are three wires, it is a 220 service, if there are only 2 it would be 110V

Typically, unless they used one standard type of cable for more than one application.
You might see three wires coming down, but only two are being used. Don’t know without seeing the application. But otherwise you are correct.

A quick question. Does your laundry area have a hookup for an electric dryer? The builder wouldn’t have put a 220V outlet in if there wasn’t 220V service available.

Or am I thinking too logically?

Thanks all for the info everyone! That Mr. Slim does look like a good alternative. I also searched a bit and saw some by Sanyo as well, like units that do multiple zones/rooms.

Got a better explanation today while armed with more info.

My current panel is a single phase or 110v one. As mentioned most AC units use 220-240v so I would need to have this matched up if I decided to use a unit like that.

I was told by the electrician:
There’s no difference to set it up either way on his part. I simply instruct him on what I want. I am to goto the city and get a permit to upgrade my panel to 200amps, the work is done and inspected by the city. If I want to use 208-240v, I let him know to install it that way, and then call the power company and they should send someone out to do the rest, should be no charge to me by the power company.

I was quoted $1400 total for the following work:

  1. Relocating the panel/fuse box outdoors, and into the adjacent wall. (also means relocating the wires needed)

  2. Replacing the panel with a 200amp unit, and if I choose have it setup to use the 220-240v. (includes cost of panel)

The relocation is moving it from inside the backmost room of the house, to the outside of the house on the adjacent wall (perpendicular)

Am I in the right ballpark price range for this kind of work? In my mind it seems simple to open up the wall, relocate the main wires to the adjacent wall, and attach a new panel on the outside and tidy up the wires. Sounds expensive to me but I don’t know much about these things.

Now I am just as confused as before. In my experience single phase is is a term used with 220V systems. When dealing with voltages above 110V there is single phase and three phase. Single phase is supplied to homes, three phase power is supplied to businesses.

The price doesn’t sound that bad (If here in LA it is a very good price) but I still want to know why 200A? As I said earlier I ran a central AC unit in my 1400 square foot house on a 100A panel. Now I fully admit that 200A would give you room to upgrade later, but how much power do you think you need?
Anyway, in particular:

  1. The electrician will have to open up the wall to access the wiring. If he is flush mounting the new box he will have to open up the outer wall also. Find out if patching is included in the estimate. In addition, an outdoor box has to be waterproof, An outdoor 200A panel runs some where over $200 just for the box. Not including the breakers. Also here in LA the way power is brought into the house has changed since my house was built. When my house was built, the power line came down from the pole and attached to a board that was bolted to the roof as a strain relief. When my service was upgraded, a 2" diameter pipe needed to extend at least 5 feet above the roof. The pole drop is secured to the pipe as a strain relief.
  2. If you are getting 200A service, what is the choose to have 220V service? You will have 220V available. As I mentioned, the outdoor panel has to be water proof, and in all likely hood need to be an entirely new part. So the new panel part of #2 is covered under #1

I would call another electrician and tell him you want to put in central air. Get an estimate. This will give you a comparison on the first guy. Write down what he tells you, and post it here. I can’t help but get the feeling that aren’t understanding the guy you have been dealing with.


First, answer everybody’s question/confusion about current service:
Between the meter and the panel should be 3 wires. How many are there? If you can’t see them. find the screw which holds on the cover of the box and remove it. then Carefully remove the cover. Don’t worry - unless you manage to dip a corner of it into the box AND contact with a BARE section of one of the wires, nothing bad will happen.
Now - how many wires, and the color of their insulation.
You want to know this yourself - it will help keep the electrician honest.
If you see 3 big, fat wires, 2 black, 1 white, congratulations, you have normal residential wiring - no new service is required to get 220 - it’s there, just not used. This is what the electrician meant went he said just tell him which you want - 110 requires 2 conductor (1 black, one white; 220 requires 3 1 white, but instead of 2 blacks, it is usual to use 1 black, the other red.

It may be useful to note that devices do not draw amps - they draw watts (watt = volt times amp). So a device which draws 40 amps at 220 would draw 80 amps at 220. Or it may not be useful to note this - if confused, ignore this paragraph.

Never mind about cycles - residences use single cycle, 60 hz. File and forget - you will never see anything wanting anything BUT single cycle, 60 hz in a home. Unless you move to some weird-ass country where they speak funny :smiley: