I have a 125 amp main panel (configuration below) for my 1250 sq ft, 2 story townhouse, and want to

  1. update my kitchen outlets
  2. have dedicated circuits for fridge, dishwasher, garbage disposal and microwave (fyi, I already have these devices, I just want to have them on separate circuits per code)
  3. add a level 2 car charger, 40 or preferably 50 amps.

My existing panel has only space for 1 breaker.

I am wondering if I can just install a 100 (or more) amp subpanel with new AFCI-GFCI breakers for the new circuits, protected by an 80 or 100 amp breaker on the main panel? A subpanel is much, much less of a hassle (and wallet-friendlier) than upgrading the main panel. Or do you think I HAVE TO upgrade service with a new main panel?

Here is how my old main panel is organized now:

  • Main (double pole);
  • 50 amp 240 V range;
  • 30 amp 240 V water heater;
  • 30 amp 240 V dryer;
  • 20 amp 240 V heater bedroom 1;
  • 20 amp 240 V heater bedroom 2;
  • 20 amp 240 V heater bathroom;
  • 20 amp 240 V heater living room;
  • 20 amp 240 V heater dining room;
  • 20 amp 120 V kitchen outlets 1;
  • 20 amp 120 V kitchen outlets 2;
  • 15 amp 120 V lights and plugs 1;
  • 15 amp 120 V lights and plugs 2;
  • 20 amp 120 V lights and plugs with dishwasher;
  • 20 amp 120 V washing machine;
  • Empty (single pole).

We do not heat or cool the house, thanks to the great climate of Bay Area. Pending the city permit on minimum heating requirements (which will take only 1 circuit remaining in the panel that is never going to be used), we will cancel and take out all the electric heaters and their wiring. So please do not mention any suggestion on heating -- it is an administrative requirement to be minimized at this stage and does not pertain to our situation.

What do you think, could a subpanel handle the load with the car charger? Thank you for your help!

PS: All to be done with permits, to-code, and with an electrician of course. I just want to outsource decision-making and not solely rely on a single person.

I also think heavily posting users here should go through a disclaimer process to prove they are responding for public benefit and not their commercial interests, is there a way to do that?

  • How many square feet is your house, and how many watts are the various (baseboard?) heaters? Mar 16 at 0:30
  • Also, do you have any local amendments that require the dishwasher and/or disposal to be on dedicated circuits? Mar 16 at 0:36
  • Can you confirm the actual watts the heaters use? A 20A 240V circuit could be loaded to 16A (3800W), but that seems pretty unlikely for separated bedrooms. Mar 16 at 0:48
  • 1
    House is 1250 sq ft; yes, dishwasher and disposal will have to be on separate (preferably 20A) circuits; heaters are 3800 but we do not use them. Two of them need repair and furthermore, the 2 1500 Watt Vornado mini plug-in heaters I bought are doing much better. Thank you for the comments.
    – Samil Can
    Mar 16 at 1:24
  • Can you get us the 99% design temperature for your area from this document? Mar 16 at 1:31

Blame all those glorified toasters for the fact your service is already oversubscribed

The source of your load calculation problem, quite bluntly, is the 19kW of electric resistance heat fitted to your house. Without it, our load calculation looks like the following:

  • 1250 ft² * 3VA/ft² = 3750VA of general lighting/receptacle load from NEC 220.12/220.14(J), and
  • 3 small appliance branch circuits (2 kitchen countertop, 1 laundry) give us 4500VA of SABC load from NEC 220.52(A)/(B)

which gives us 4838VA of factored general load (using the 35% demand factor for general + SABC loads over 3kVA, as per).

Then, atop that 4838VA of factored general load, we add our heavy appliances:

  • 8kVA for a range under 12kVA as per Table 220.55 Column C for a single range (let us know if your range is bigger than that)
  • 4.5kVA for the water heater, and
  • 5kVA for the dryer as per NEC 220.54

which gives us a reasonable 22338VA, or 93A @ 240VAC, for your house before we add the electric resistance heat. However, that 60+kBTU/hr of resistance heat, by itself, takes up 3800VA * 5 heaters * 1.25 due to continuous load factoring (NEC 424.3(B)). This adds up to 23.75kVA of load, or another 99A at 240VAC; atop that, it's also a NEC violation right now as NEC 230.23(A) requires services to be large enough to handle their Article 220 calculated loads:

230.23 Size and Rating.

(A) General. Conductors shall have sufficient ampacity to carry the current for the load as calculated in accordance with Article 220 and shall have adequate mechanical strength.

The answer to the question you should be asking, but haven't yet, is a heat pump

However, those space heaters just won't cut it for keeping the whole house warm, especially during a cold snap where at-risk piping can easily freeze up and make a mess. As a result of that, homeowners insurers require working central heating systems, and so do the building codes, for that matter. In the IRC, this requirement is found in R303.10 (the Table R301.2 reference is really a reference to the 99% temperature from the ACCA Manual J tables):

R303.10 Required heating.

Where the winter design temperature in Table R301.2 is below 60°F (16°C), every dwelling unit shall be provided with heating facilities capable of maintaining a room temperature of not less than 68°F (20°C) at a point 3 feet (914mm) above the floor and 2 feet (610mm) from exterior walls in habitable rooms at the design temperature. The installation of one or more portable space heaters shall not be used to acheive compliance with this section.

The question then is "how can you heat your house without consuming most of your service?" Fortunately, heat pump technology has made leaps and bounds since the early days; today's mini-split heat pumps can defrost without strip heat and have efficiency ratings that put most of the air conditioners you're used to seeing to shame. Furthermore, you can get them in capacities up to 5 tons (60kBTU) nowadays, with either a single large indoor unit similar to a conventional air handler feeding a full duct system, or multiple smaller indoor units that either feed flat "pancake" ducts or serve single rooms/areas.

So, given that your manual J design temperatures are around 40°F, I'd get someone qualified to run an ACCA Manual J, Eighth Edition calculation on your house, and then have them use Manual S to size a new heat pump from there. This will let you decommission all those costly resistance heaters and enjoy both efficient, reliable heat in the winter and air conditioning in the summer. And when I say efficient, I mean more than twice as efficient as your resistance heat; using a LG LMU600HV as an example, it consumes a mere 32.2A @ 230VAC, or just over 9.25kVA of load. Keep in mind that this is essentially a worst case figure; real-world numbers will be better than this, especially if you can leverage some envelope upgrades (insulation, air-sealing) to knock your heating load down further.

But, those car charger plans also call for a service upgrade

While replacing the resistance heaters with a heat pump gets you back within the realm of what your existing 125A service can handle, adding that 40A or 50A car charger load (really, 32A or 40A times 1.25) to the picture is enough to put you well over 125A of service ampacity. So, in order to cover that, you'll need to have a service upgrade done anyway; the good news is that getting rid of those glorified toasters lets you upgrade to a relatively inexpensive 200A service instead of forcing you into much costlier Class 320 service hardware.

When you're having the electrician put the service upgrade in, make sure that you get plenty of panel spaces; while the extra kitchen branch circuits don't add much load, they do take up a fair few spaces, and nobody ever complains about having too much room in their panel! In fact, I'd go with a 40-space or 42-space panel as a minimum specification for this service upgrade; if you can get a 54-space or 60-space panel, or a pair of 40-space or 42-space panels either fed in parallel from a meter-main or daisy-chained together, that's even better.


You HAVE to do something here

The "elephant in the room" is exactly what you discovered with the load calculation vis-a-vis your toaster heaters. You might want to ignore that elephant in the room, but since you want to do the EVSE upgrade "legit" with electricians and permits, you can't.

No electrician will touch a panel as oversubscribed as this one (except to correct that), and no AHJ is going to issue permits for even more load until the existing load issues are resolved.

"I'll just remove all the built-in house heaters" -- no, you said you wanted to do things to Code. Building codes require houses to have functional, built-in heating systems. If they didn't, the obvious thing would happen: people would just use portable heaters as a substitute. That creates a myriad of safety problems (and policy issues) and that's why it's Code.

Given that baseboard heating is notoriously cheap to install but nosebleed-expensive to operate, we know the builder was cheap. That tells us the builder didn't install any more toaster heaters than the Codes required, so most likely replacement toaster heaters will need to be that size/ampacity. Your calculation was correct, and if you stay with toaster heaters, you'll need 200A of service just for what you have now, and the EVSE will require a bump to a larger 300 or 400 amp service.

That is an expensive proposition since it involves changing so much stuff. As such, it may actually be cheaper than that to upgrade your high-draw appliances. Not only save a great deal on every electric bill going forward, but also possibly avoid the expense of a service upgrade.

So... I know you didn't bargain for such a daunting project as changing to a completely different heater tech OR getting 200A service just to keep your occupancy permit... but aren't you glad you asked now? LOL well no obviously, but it is better than the other scenario: planning out the EVSE project, getting well into it, and then getting blind-sided by this. Getting blind-sided mid-project usually means desperately rushed choices, second choices, and much greater overall expense, as contrasted with a smart, pro-active approach.

I would rather put those tools in your hands. That's what we do here.

Stop using the plug-in heaters

They're dangerous. And they were never intended to be run unattended. Read the UL-approved instructions; they say that flat-out. They are highly prone to starting fires, and their fire protection strategy is you in the room smelling the smoke. Use them for accent heat when a room is a bit too drafty.

"But they're more efficient" no, they are not. The one redeeming quality of ALL toaster-heaters (the wall units and the portables) is they are ALL 100% efficient. They turn electricity into heat.

(by the way, roll that video back to the start if you want more about those portable heaters).

How can they be 100% efficient? Entropy. Heat is the ultimate, unavoidable destination of all uses of electricity. Whether it's a 1500 watt blender, 1500 watt laser printer, or 1500 watt (actual) grow lights... all of them add 1500W of heat (5120 BTU/hr) to the room. Your heater just cuts the corner and goes straight to entropy, rather than mining Bitcoin first. They don't have vents and there's nowhere else for the heat to go.

"But they do save money" actually you're just running the rooms colder... you could do the same thing on the built-ins just by turning down the thermostat. It doesn't feel so bad because you're aiming the portable heater at yourself. Here in my computer hutch, 700W boils me out of the space - but it doesn't barely heat the room.

"But the built-ins have expensive, complicated problems" -- they can't possibly. They are too simple. A brand new 2000W Cadet baseboard heater is $57 at Menards, and guess how efficient it is?

Got it in one :)

Electric toaster heating is dirt cheap (to buy, and the most expensive to run). That's why it was installed on the house in the first place... though I guarantee you the AHJ did not approve that load calculation.

Going heat pump? Keep going...

I know you view your house as "tiny", but it's a dynamo (well, the exact opposite) of high-draw electric appliances. It's clear you don't even have gas coming into the building. This is typical "all electric" housing stock circa the 1950s when "cold fusion" was just around the corner, and electricity would be "clean, safe and too cheap to meter". Seriously - they actually believed that, and were building houses with that mentality. It's still in full force in places like Ontario, Washington, North Carolina or Ukraine which have a glut of hydro or nuke power. They even have electric rate plans which are extremely favorable to such houses.

Toaster heating is "cheap-o" from the builder's perspective, but it is the most expensive heat possible from the owner's perspective. Any other heating tech will save you a ton of money, which is why we are discussing it. If you do not pay for your electric bill, then nevermind...

But you can take ThreePhaseEel's "heat pump" concept and keep going with it, and maybe get the headroom on your existing 125A service to run the kaboodle including EVSE.

Heat pump aka "condensing" dryers -- these take advantage of the fact the goal of a dryer is to dry clothes, not heat clothes nor eject hot air from the house. They replaced the dryer's heating element with a dehumidifier. They are tumbling the clothes in very dry air, and pumping the condensed water down the washing machine drain. The process heat (inefficiency i.e. entropy) from the dehumidifier also warms the clothes somewhat. Instead of running 5500 VA (actual) like normal dryers, these come in at 2400 VA. (almost enough to run on a 120V).

Note the condensing dryer doesn't have any outlet - everything stays inside the room (except for the condensate going down the drain, and that'll be cooler-than-ambient). So heat energy has nowhere to go, and it actually warms the laundry room.

Heat pump water heater. These do the "heat pump" trick, again, with water heat. However, unlike the dryer, they do have an outlet: the mass of water in the heater. Therefore they do steal heat from the utility room, making it very cold. In cold weather, your home's heating system must "make that up". In hot weather when you want air conditioning, you get a "free ride"! Really! You remove the heat from the house when the hot water goes down the drain. But again, they use a great deal less energy directly, and that affects your load calculation favorably.

Unfortunately, they don't make heat pump ranges. But they do make gas range/electric ovens, and the reason to consider that is that ranges don't need exhaust vent stacks, so no construction and roof penetration needed. It also uses comparatively little gas, so the normal truck-filled outdoor propane tank will last a long time.

You can compare the upgrade cost of some or all of those appliances to the cost of a service upgrade.

  • Great answer, as usual. My only comment is that at least in my area (Maryland), all-electric houses were not a 1950s thing. They were a 1970s "oil crisis" thing. I grew up in one of those houses. Everywhere else in the neighborhood (it was a unique house replacing a very old one) has natural gas - we didn't. Even though natural gas was from the USA, it got lumped with oil from Saudi Arabia to force all-electric houses. Absolutely crazy. Did eventually get natural gas - about 20 years later. Meanwhile my house has natural gas but had (like most in my neighborhood) electric cooktop because Mar 16 at 19:04
  • electric was the "new & shiny" thing in the 1950s - when I redid my kitchen pulled gas line from literally right underneath the kitchen so I could be cooking with gas. (And separate oven, so still electric oven - best of both worlds.) And yes, when I was growing up we froze in the winter because the baseboard heaters were way undersized. Mar 16 at 19:05

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