There are a lot of reasons why you might want to move your home toward being fully electric, whether it's principles – your home's carbon footprint, dependence on foreign oil – or practical, like rising fuel costs or solar financial incentives. In any case, most of our houses weren't built to take full advantage of modern, efficient electrical systems, so it's worth doing some homework and planning. This is a quick primer on the core concepts so you know where to focus.
If you move to use electricity for everything in your home, you'll be using more electricity than you likely have in the past, so driving the cost of that electricity as low as possible is usually a great move. Here in Massachusetts, we have very high electricity rates, and there are currently some pretty decent incentives for solar installation, so putting solar on your roof can be a critical way to make this all sustainable.
Solar power systems cost a fair bit to install, but cost approximately nothing to run over the years, so this is an investment in the future. Right now in 2022, with Massachusetts' high electricity rates, you can expect a typical solar installation to pay for itself in approximately 5-7 years. Here are some key things to know:
- Check out your roof – Ideally, you have a large, flat, south-facing roof without too many pipes, skylights, or other obstructions, and no big trees blocking it. Every thing on your roof makes it harder to fit a panel, and as we'll discuss below, you want to fit as many as you can. Check out Google's Project Sunroof for a great first-glance analysis of your roof and its potential for solar. Once you know it's viable, consider the condition of your roof – you won't be able to replace or repair your roof in the future without removing the panels, so you want it to be in good shape from the outset. If you've replaced your roof in the last few years, you're probably set. If not, this might be a good time to think about it, and consider air infiltration (covered later below) while you're at it. In general, your panels will be protecting your roof too, so a new roof will last longer as a result. Your solar installer will also give your roof a check, because they have an interest in this too.
- Go as big as possible – In Massachusetts right now, we have net metering, where every kilowatt-hour of power you generate is worth the same as a kilowatt-hour sold to you by the electric company. If you use 200 kWh in a month and generate 150 kWh, you'll only have to pay for 50. If you generate 250, the electric company will credit your account for 50, like rollover minutes on old cell phone plans. In fact, with the current SMART program in Massachusetts, they'll cut you a check each month for even more. So it's generally to your advantage to have as large a system as you can, provided that the panels are generally able to produce decent power (facing south, no trees, etc). Home systems are typically 5 to 10 kW in capacity – ours is about 9 kW, and it covers all our electricity for 9 months of the year, but isn't enough to handle all the heating in the winter.
- Batteries may or may not make sense – Since we have net metering (see above), the utility company basically acts like a big battery for us. The excess power you generate during the day is "sold" to the grid, and then you are getting it back at night when your panels aren't generating anything. So batteries are really most useful for power outages. If you have power outages often, maybe this is worth it. If not, it might not be. Batteries are most worthwhile in areas that have time-of-use metering, where power at night costs less than power during the day – so you can run things off solar and batteries during the expensive hours and use the grid at night. But we don't have that in Massachusetts right now, so it isn't a major factor, and you can generally add batteries later if things change (though it's a little cheaper to do it all at once). You may also be able to use your EV/car as a battery, so consider that option too as a nice cost-saver.
- Things are changing fast – Every year, panel get cheaper and more efficient. We don't know when that's going to stop. But like a computer, you can be pretty sure that what you buy this year will seem lame a few years from now. The only thing to really consider is when that break-even point is, and if you're happy with that, it's a good time to buy.
- There are design options – Some panels look nicer than others. This could be really important to you if, for instance, you're putting panels on the front-facing side of your roof. You can find panels that don't show the grid markings, have nice trim, and so on. We went with Solaria panels.
- Microinverters are cool – Traditionally, all the panels would be wired together and then into a big inverter which makes the power appropriate for your home. This has some downsides, like shade on one panel affecting the performance of all panels. Microinverters use a separate inverter for each panel, so each can operate independently, giving you a nice boost in output. If one panel has an issue (damage, shade, malfunction), the rest will just keep doing their thing. Our panels use Enphase microinverters. Enphase's tracking software, which shows how much you've generated, is reasonably decent too. Quick tip – this tracking software needs to be connected to the internet, and a lot of installers get themselves a bit of extra money by selling you a cellular modem to connect your system to the internet. If you have decent wifi, you can just use that and save yourself a few hundred dollars or more. Need better home wifi? I have some tips for that.
- Consider a couple extras – If you have trees near your roof, and squirrels get up there, consider asking for trim to block critter access, since squirrels love eating the wires, and that usually isn't covered by your warranty. Consider asking for snow guards to help keep snow from avalanching off the roof, which is a bigger deal with the slippery panels than it is with your grippy roof today.
- Get competitive bids – There are a lot of installers. Go on Energy Sage to get competitive bids, and talk to a few of them. See who is doing their homework on your home, get a reference or two from your neighborhood if possible. We used Great Sky Solar, an employee-owned co-op in Cambridge, and had a good collarborative experience with them.
- Consider the warranty – Your installer is going to give you a warranty on your system. Part of this warranty is dependent on the warranty for the panels themselves, and part is for the service of the whole system. A long warranty is great, but warranties are only as good as the company providing it, so consider whether you trust that the installer is going to be around for a while. That said, most solar power system issues occur within the first year after installation – if you get through a summer and winter without an issue, you probably won't have an issue for many years.
- Beware of Tesla – Tesla makes cool products, good-looking panels, nice batteries, decent software, but their service is a pain in the butt. They're unreliable, tough to get in touch with, and have been the source of huge frustration for several friends. Again, once it's all working, you don't have to really deal with them much, but it was too much of a headache for me and I got my deposit refunded, which is too bad. But your mileage may vary, and you may be more patient than I am.
There's a lot to this, so we can't be anything close to exhaustive here, but there are some fundamental differences between HVAC systems using furnaces and electric systems, which (should) use heat pumps.
Heat pumps are air conditioners running in reverse, taking heat found in the air outside (even when it's cold) and dumping it into the air inside. There's not nearly as much heat to work with as a furnace, which is lighting a fire (with either oil or methane/gas), so heat from heat pumps tends to be low-and-slow. Heat pumps usually run all the time during a heating season, speeding up or slowing down as needed to keep the house at a constant temperature, rather than a furnace which lights up and turns off as needed.
As a result, in a heat pump home, everything is a radiator: if your thermostat is at 70 degrees, the heat pumps are trying to keep everything in the house at 70 degrees all the time – the furniture, countertops, doorknobs, all at 70, 24 hours a day. A well-constructed heat pump system is often described as comfortable, with everything feeling nice and even.
This process can be very, very power-efficient. For every bit of energy it uses, a heat pump system can bring three or four bits of heat into the house. A good system, in a good house, can be heated all year with the same amount of power as a hair dryer. In fact, if you turn the thermostat down at night, you're actually going to wind up wasting energy, since heat pumps are less efficient at making big corrections in temperature, and more ideally are just constantly making small tweaks.
Heat pumps used to fail in cold weather, so a lot of out-of-date HVAC pros don't like to use them in cold climates. This has changed in the last decade. Heat pumps from some manufacturers can now operate down to -13F, but you'll want to make sure you buy one designed to do this.
But the low and slow comfort produced by heat pumps is also a bit more fragile than throwing a big fire at the problem with a furnace. The biggest foe of a heat pump is air infiltration, and you'll want to be sure you have a handle on this in your house before using a heat pump.
Importantly, most heating systems in the US have traditionally been oversized for the house. That means that if a house needs (for instance) 100,000 BTUs of heat to keep things comfortable on a cold day, the HVAC contractor might say "well, let's do 200,000 BTUs to be safe." And usually homeowners nod and approve. But oversized HVAC systems are very inefficient and can cause all sorts of noise and comfort issues.
Even a mediocre HVAC contractor should perform, at minimum, a Manual-J measurement on your house, which takes room size, window/door size (and position), materials, and other factors into account to determine the "heating load" of your house. That is, for a given design temperature, how much heat would it take to keep the house at a comfortable temperature? Most HVAC contractors perform a Manual-J using an app on their phone or ipad.
Design temperature is worth paying attention to. Statistially, in Boston, it's above 12.3F 99% of the time, and above 7.7F 99.6% of the time. So if your system doesn't operate at peak efficiency at 5 degrees F, that's not a huge deal, because it's quite rare.
So if your HVAC contractor performs a Manual J that determines that your home requires 50,000 BTUs at a design temperature of 7.7F, you can be confident that a heat pump with a 50,000 BTU capacity at that same temperature will have you covered 99.6% of the time. Having a 75,000 BTU heat pump won't really be helpful to you, and maybe some resistance heat strips (which are very, very cheap to buy) will be the insurance policy you need. See "Backup heating" below.
But if your contractor is using other shortcuts, like "600 BTUs per foot of basebord radiators", then not only are they not getting an accurate measurement, they're basing the heat load of your house on what someone did decades ago. And then they might round it up further to be safe, and you're just compounding the errors.
Be sure they're doing an accurate load measurement, and this is the first sniff test in finding a reputable contractor. The system likely should be much smaller than your current one.
Lastly, if you're going to be doing any insulation or air sealing work (you probably should, see below), you'll want to do these before calculating the heat load, since they can dramatically improve your heat load calculation, and therefore make the new system even smaller and less expensive.
When we think of comfortable houses in New England during the winter, most people think of insulation. It's important to have a reasonably-insulated house, but when working with heat pumps, it's far more important to avoid having a leaky house. The slow, warm air put out by heat pumps is super happy to GTFO through every crack and crevice in your house. A furnace just keeps pumping fire at the issue, but heat pumps need a tight house to be efficient.
You can think of insulation like a sweater and air sealing as the wind breaker. On a cold, windy day, the wind goes straight through the sweater and you're cold. But the wind breaker, even though it's thin, can help keep you much warmer. You need both for your house here in New England, and most people forget about plugging the leaks, and their house is more like a sweater than a windproof, insulated coat.
How do you know how leaky your house is? A blower door test. This is a tool that gets put over your [front] doorway, and has a big fan that pressurizes your house slightly (50 pascals) to simulate what happens on a windy day. It measures how much air is being pulled in from the outside through every part of your house. You can do it on individual rooms too, but it's usually done house-wide. The resulting statistic represents how much air gets replaced at that pressure, and is expressed in either cubic feet per minute (CFM50) or uses your house's size to calculate the number of air changes per hour (ACH50). ACH50 is a bit more popular and is actually part of the building code nowadays – an ACH50 of 5.0 means that during the course of an hour, air filling five times the volume of your house moves through your walls/ceilings/doors. We worked with Infrared Diagnostics to get our blower door test, and he also did some useful infrared imaging to actually "see" the leaks and help prioritize.
So what's a good figure? Lower is better. For new construction in Massachusetts, code is 3 ACH50 or lower. In other states with older building codes, it's 5 ACH50. A "pretty good house" in the industry is 1.5 ACH50, and a "passive house" is 0.6 ACH50. If you have an older house, there's almost no chance you're anywhere close to these numbers. Our house was 10.5 ACH50 after we'd done a little air sealing work. For heat pumps to do their job respectably, folks generally think that something like 7 ACH50 and below is a good target to start with.
Here are some thoughts:
- If you're replacing your siding anytime soon, you can take the opportunity to make some great progress by installing an air barrier under the new siding. Air barriers are most commonly "house wrap" – this is the wind breaker.
- Mass Save offers free air sealing from their insulation contractors. Unfortunately, none of this work involves a blower door test, so it's just a bunch of guys spraying cans of foam in places they guess might be leaky, and there's no demonstration of good results. Still, it's not nothing, and it's free.
- Without house wrap, air is getting through every seam in your home's drywall. Cracks, outlets, switches, windows, window frames, doors, door frames, joints where the paint is broken... it's a lot.
- The two main tools of air sealing are caulk and foam. Spray foam, good caulk, and a battery-powered caulk gun will be your best friends as you hunt down and fix gaps.
- If you have a fireplace, it's worth giving this some attention, since most fireplaces are pretty air-leaky. A good set of fireplace doors, sometimes marketed as "air-tight," can really help this. They're usually not truly air-tight, but they can be pretty good and dramatically improve draftiness. Even regular fireplace doors, without air gaskets, can be a significant improvement, as long as you keep them closed when the fireplace isn't in use.
Windows deserve some special attention:
- Old windows are old, and usually super leaky. You can add weatherstripping to your old windows and give them a cheap, quick, and not-insignificant upgrade – see this video from Ask This Old House which gives a solid overview.
- If you use spray foam around a window, be sure to use special window foam, which doesn't expand as aggressively. Regular foam can put pressure on the windows and make them harder to use.
- Storm windows help too, and newer storms do a decent job of air sealing.
- We actually got interior storm windows for ours, from Indow, and they have done a pretty nice job. They're clear, custom-made to your windows, and can be easily taken out in the springtime if you want to open the windows up.
- In a pinch, plastic film kits like this one do a fine job and the price is right, and can look practically invisible if you're careful how you put them on.
As mentioned above, if you have a reasonably level of insulation, air sealing is king. But you still need to get to a reasonable level, and a lot of older homes have literally no insulation (that was true of ours).
What's a reasonable level?
- Ceilings & Attics – Code is R-49 in new construction, and this is probably where it's most important, so get whatever you can. Foam insulation is about R-5 per inch, so that'd be 10" of foam, while loose cellulose is R-3.5 per inch, so that'd be around 15". If your attic doesn't allow that sort of depth, just fill with whatever space you have.
- Walls – Code is R-20 (in general), and that's going to be tough to do in an old house. Dense-pack cellulose is nearly R-4 per inch, so if you have 2x4" wall framing, you'll get something like R-10 to R-12 if it's done well.
- Basements – Code says basement walls should be R-15 and basement slabs should be R-10 (yeah, you insulate the slab floor these days!). Mass Save doesn't cover most of this sort of stuff, but they do cover insulating the rim joist, which is where your foundation/basement walls meet the wood framing for the rest of the house. Getting the rim joist insulated and air sealed can make a really big difference!
There are a few different materials you can use, each of which is great for different purposes:
- Fiberglass batts – This is the pink, itchy stuff. It delivers about R-3.5 per inch. There's usually a better option than using this, but this is cheap and ubiquitous.
- Mineral wool batts – This is the upgrade pick over fiberglass. It's slightly better insulating (R-4 per inch), isn't as irritating, fits tightly between studs, provides decent soundproofing, and is much, much easier to work with. If you have walls open, you can totally do this yourself with a bread knife and a measuring tape.
- Cellulose – This is a pretty good, pretty cheap insulator. It's best used in attics (loose, just dumped on the attic floor, which gives R-3.5 per inch) and blown into walls from the outside (dense-pack, which gives R-4 per inch). It requires some special machinery to install (a big blower), and would certainly be a part of most Mass Save projects.
- Rigid foam – This is like styrofoam, which was used for coffee cups and take-out for a reason. It's light and insulates pretty well, and actually provides its own air sealing. There have been some improvements over styrofoam, but the principles are the same. You can use this almost anywhere, but it's perhaps most useful on the outside of the house, where you can sheet it up against the outside walls, under the siding, and get both air sealing and extra insulation all at once (assuming you do a good job taping the seams). Polyiso provides R-6 per inch (though slightly less when it's particularly cold), XPS and EPS (EPS is better for the environment) provide R-5 and R-3.6 per inch respectively. Sometimes you can find used rigid foam insulation, which can be perfectly great to re-use, and the price is right!
- Spray foam – There's the simple spray foam you buy in cans from Home Depot for air sealing (R-5 to R-6), which is pretty good, but would be tough to use for larger areas. Then there's the stuff you see on HGTV, a two-component, closed-cell spray foam that provides R-6.5 per inch over a larger area. Closed-cell spray foam can be expensive, but it also provides its own air sealing. This isn't usually very DIY friendly, but you can get the kits yourself if you really want to.
More thoughts:
- Most of the time, you'll want to use Mass Save for this. There are steep discounts on insulation work, and while it doesn't cover spray foam, it can help get you up to a reasonable level. Again, the contractors aren't always doing their best possible work for Mass Save, but the price is right.
- Generally, an insulation contractor will remove a row of siding, cut holes into your outside walls, and blow in cellulose under a decent amount of pressure (dense-pack).
- There are a bunch more details to this, especially for bigger projects – like, if you're using rigid insulation on the outside of the house, you need at least R-7.5 (2x4 framed walls) or R-11.25 (2x6 walls) of exterior rigid insulation to make sure you don't have moisture issues. If it's a big project, consult someone who knows what they're doing to make sure the plan makes sense.
If you have ducting in your home, the process can be hypothetically pretty simple. The air conditioner unit outside your home can be replaced with a heat pump model (which is a premium option, but not ridiculously expensive). Depending on your system, you may want/need to replace the air handler inside, or even add a great filtration module to improve indoor air quality. You can keep your existing furnace in place as backup heat, or remove it if you don't need it.
If you don't have duct work – perhaps you have radiators like a lot of homes in the area – there are three main options for heating:
These are those high-up-on-the-wall units you've seen more commonly over the last few years, especially in businesses. They're called "splits" because the compressor is outside – a large fan in a box on the side of the building – and the air handler is inside. The compressor heats (or cools) a refrigerant and pumps it indoors, where the air handler unit passes your room's air over the coils containing the refrigerant and blows it out. Minisplits are most popular for air conditioning, but the heat pump models are perfectly great at heating too.
Tips for folks considering mini-splits:
- In Massachusetts, you'll certainly want models designed for cold weather. We have Mitsubishi models with Hyper Heat and they have done a fine job for a few years now, and operate down to -13F.
- You can hypothetically put one air handler unit in each significant room of your house, which is nice for allowing each room to have its own temperature control. Typically, one outdoor unit can handle up to 4 indoor units. We did this, and it generally works fine, but it turns out that these units aren't as efficient as single outdoor/indoor paired unit. If you have an open floor plan, a single unit can generally handle the whole floor, and the tech will be more efficient. Bedrooms are trickier here.
- If you have an unfinished basement or attic, you can actually consider adding some minor ductwork to a minisplit unit to get the best of both worlds. Have a single outdoor unit power a large air handler in the attic, then have ducts in the attic that run to each bedroom. You can do the same thing upwards from the basement. Efficiency that works for multiple closed-off rooms.
- While the units high up on the wall are the most common, there are floor units too, which are arguably more efficient for heating purposes. We have one floor unit and several wall units, and I wish we had more floor units. These look no more obtrusive than a radiator, and shoot the air down at the floor to rise up, rather than wall units which shoot the air downward from above. Heat rises, so...
- Work with your contractor on how the linesets (outdoor piping) is run so that it looks aesthetically the way you like. Perhaps running it alongside a downspout from your gutters can make it less noticeable, or perhaps you can focus them on one particular side of your house.
If you're edgy and modern, you can look into these new air-to-water heat pumps, which have existed for a while in most of the world, but are just starting to get used in the US.
With an air-to-water heat pump, you can basically just keep using your radiators like you do now, but the water will be heated by the heat pump rather than a furnace. Normal heat pumps can only get water up to 130F, which usually isn't enough for the cast-iron radiators we have in older houses in New England, but the newer CO2 heat pumps can go up to 150-180F, which does the trick.
Most commonly, these function like mini-splits, where there's a compressor outdoors and a unit indoors to heat the water. You can also use these for hot water.
You'll definitely want an experienced professional involved in this, since it's relatively new.
If you don't mind tearing up walls or using parts of closets, it might be worth exploring adding ducting to your home, in which case you can just treat it like a ducted house. You'd also be able to get rid of your radiators in this case, which might free up some space.
Heat pumps stop working in two cases:
- There's no electricity
- There's not enough heat in the air
The thing most people don't realize is that your oil or methane (gas) furnace doesn't work without electricity either. So if there's a power outage, you won't have heat either way. You probably don't have battery backups right now for your furnace and haven't cared about it, so it's probably not worth caring too much more about that now. But if you decide to have solar with batteries (or an EV that works as a battery backup), then you'll be better off than you are now – but since electric heating uses a lot of electricity, this might last you a few hours. In the event of a multi-day power outage, you won't have heat during that time.
But if it gets too cold (below -10F or so), that can get dicey with heat pumps. Here are the thoughts:
- It's pretty rare to get that cold. The last day it was below -10F in Boston was in 1957, when it got to -12 for one day. In the last 130 years, there have been 9 years that recorded a day at or below -10F, and none for (as mentioned) 65 years.
- For ducted homes, traditional air conditioner/heat pump combo units often come with resistance heat strips for situations where the heat pump can't keep up. These aren't as power efficient, but the idea is that they'd be fairly rarely used.
- Those heat strips are basically a space heater, so if you have mini-splits, you can have space heater or two on hand for these worst-case scenarios.
- The better insulated and air sealed your home is, the longer it will retain the heat it's already produced. So if you're in good shape on that front, your home might stay warm (or at least tolerable) more easily.
You may have a domestic hot water (DHW) system that is powered by your furnace (either oil or methane/gas), or you may want to replace your stand-alone methane (gas) hot water heater. There are two main options today, and one option on the horizon in the next few years:
- Resistance instant water heater – This uses resistance heat (hot coils, like a space heater) to heat water as it passes through. These can be reasonably small (mounted to a wall), tankless, and usually heat water on-demand when you turn on a faucet. Even though they're on-demand, it takes quite a lot of electricity to heat water quickly, and if you need to power multiple showers at the same time, it can take a beefy heater to handle it all. You'll work with a plumber and electrician to figure out the size you need and wire in a dedicated circuit to handle it. This is just about the most expensive way to heat water, and I generally wouldn't recommend it unless space was your top consideration.
- Heat pump water heater – This uses an air-source heat pump (like we talked about in the HVAC section) to draw heat out of the air and put it into the water. This isn't a quick process, so HPWHs are attached to a water tank. Unlike a traditional tank water heater, where larger models are less efficient because they need to keep heating all that water, since heat pumps are slow and gradual, the larger tanks actually act like a sort of battery for the system, storing the generated heat relatively efficiently with the help of a lot of insulation around the tank. Many HPWH models are "hybrids" and have a resistance heater built in as a backup in case you're running low and need hot water in a hurry. You'll need a decent amount of air space for the heat pump – if it's in a closet, the closet door will need ventilation to the main space – and the heat pump will make the air slightly cooler (generally by a degree or two). The heat pump will also act as a dehumidifier, so it can be a nice benefit if you have it in your basement. If you do keep it in your basement, and your basement gets cold during the winter, the heat pump won't be as efficient, though it should work fine down to the 40s. You'll want to make sure your basement doesn't run the risk of freezing if the heat pump drops its temperature slightly.
- CO2 heat pump water heater – In a few years, we should have readily-available versions of heat pump water heaters similar to mini-splits, where the compressor is outdoors and heats a refrigerant (CO2 in this case) to provide heat to water, even up to 180F, quite efficiently. You can get one of these today from ECO2, but there'll be more and better competition soon.
If you're replacing a methane (gas) dryer, you have two main options:
The standard electric option, these have been around for decades. They use resistance heat to heat the air in the drum, drying the clothes, and venting the warm moist air outside. Resistence heat is relatively inefficient, but it's an effective option in this case. You can get these in any size, with normal ones being in the 7-10 cubic foot range.
You'll need a dedicated 30-amp circuit and breaker for your electrical dryer, wired to a 220-volt outlet. This is pretty ordinary and standard.
Just like a heat pump for your home, these dryers act like an air conditioner in reverse, dehydrating the drum and drawing the water out that way. There's significant efficiency to this (50% or more!), though it's not quick. Heat pump dryers are typically smaller than electric dryers, at around 2-3 cubic feet, and can fit into a smaller/shallower space. They can take up to twice as long to dry clothes, and since they aren't heating them as much, they don't do as tidy a job at removing wrinkles.
Aside from the efficiency, another benefit is that these dryers generally don't have to be vented to the outside. So you can put these in more flexible locations than a traditional dryer.
You'll generally need a dedicate 20-amp circuit for a heat pump dryer, though some are designed to share a 20-amp circuit with an efficient washing machine. You'll also need to run a small water line into a drain so it can expel moisture. Your washing machine needs to be drained too, so this usually isn't a huge deal.
Most modern ovens are electric anyway, so you'll probably just be thinking about the cooktop here.
However, you might want to consider a countertop oven anyway, since large ovens take a lot of time (and energy) to heat themselves up. If you usually do small-to-midsize meals, a countertop oven can be a really nice convenience. We used the Breville Smart Oven for about ten years before replacing it recently with an Anova Precision Oven which can handle a small turkey and has a bunch of nifty features.
Back to cooktops:
- Methane (natural gas) cooktops are a huge contributor to poor indoor air quality, and a leading cause of asthma.
- Regular electric cooktops are pretty inefficient and use a ton of electricity. They're inexpensive though, so if that's what your budget calls for, there are good options.
- Induction cooktops are the future. They're reasonably efficient, make boiling water very quick, and reduce the risk of burns and fires. You can buy a portable induction hob for $50-100 and try it out for yourself to see how you feel. We bought this one and it's pretty great.
- If you're replacing a methane (gas) cooktop with induction, you'll need an electrician to run a line. Usually this is a 30, 40, or 50-amp breaker, right alongside the one for your oven.
Lots of folks have EVs now, so I won't write too much here, other than to say that it's a pretty big electricity consumer. So you'll want to make sure you have a main panel that has enough juice to allow you to charge it reasonably quickly. Generally, if you have a 200 amp panel, you'll be okay.
Some cars also have the ability to act like a battery in the event of a power outage, so consider working with an electrician to take full advantage of that if possible.