EV Home Charging Typically Draws Less Than Half The Power Of An Electric Furnace

JAN 7 2018 BY MARK KANE 61

In addition to the average annual energy usage, the US DOE’s Office of Energy Efficiency & Renewable Energy has also compared electric vehicle power draw to some other common electric appliances (there must not be a lot of other things to do at the DoE office these days).

In most cases, electric vehicles need to be supplied by up to several kW of power, which is actually below most electric furnaces when in operation, although there are some plug-in models with 10 or 20 kW home systems (such as Teslas with double on-board chargers).

Similarly in Europe, the highest home EV charging units end at ~22 kW (three-phase), such as the case with the Renault ZOE. Higher powers output can still occur, but it is extremely rare anywhere in the world.

Power Draw for a Typical Appliance (source: energy.gov)

If you are looking to purchase an electric vehicle, and are considering what power level to install in your home today – it would be good to have 7.7 kW (32 A @ 240 VAC) or more system on hand, even if your current plug-in choice can take all that juice (you might be able to utilize it in the future). In Europe however, it’s a smart idea to have 3-phase installation, good for 11 kW or 22 kW to be ZOE-proof, or at least future-proof (as currently most models are still equipped with single-phase chargers).

Electric vehicles can be charged at power draws comparable to various household appliances. Most electric vehicles charging at home on a 240-volt level 2 charger will draw about 7,200 watts or less.

For comparison, a typical electric furnace draws about 10,000 watts and a water heater uses 4,500 watts. The power draw for an electric vehicle is limited by either the electric vehicle supply equipment (EVSE) or the vehicle’s onboard charger which limits the rate of electricity the vehicle can accept.

Many first-generation plug-in vehicles have onboard chargers limited to 3,600 watts, similar to the power draw for a typical home air conditioning system, while newer electric vehicles have increased onboard charging rates. Some owners use only a standard 120-volt household outlet (level 1 charging) which has a very slow charge rate and low power draw compared to the level 2 charging. There are some electric vehicles, such as those produced by Tesla, that allow for even greater home charging speeds and higher power draws similar to an electric furnace. While an electric vehicle can draw a considerable amount of electricity when charging, the overall fuel cost for an electric vehicle is lower than a comparable gasoline vehicle.

Notes:

  • Level 1 charging assumes the 12-amp setting is selected.
  • In colder climates, an electric furnace may draw 20,000 watts.
  • For comparison, a 2013 Nissan LEAF is rated at 115 MPGe (miles per gallon equivalent) and a conventional 2013 Nissan Versa is rated at 35 MPG. This results in a cost of 3.8 cents per mile for the LEAF and 6.7 cents per mile for the Versa at 13 cents per kW-hr and $2.35 per gallon of gasoline.

Source: energy.gov

Categories: Charging

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61 Comments on "EV Home Charging Typically Draws Less Than Half The Power Of An Electric Furnace"

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DL

Do many households really have electric furnaces? Coming from an area with plenty of natural gas, the largest electrical draw for me has always been the A/C, at around ~4000W max. Even if I didn’t have gas I’d have a heat pump, not an electric furnace.

Ken

Yes, where I live in the Pacific Northwest, electric heat is very common. We have tons of renewable energy mostly from hydro-electric and the West never built out a deep natural gas or oil infrastructure.

Bill Howland

For the rest of us Ken, please list your per kwh rate, and if Time-of-day is available, please list day and night rates of those also.

If possible, list fixed costs (billing charge, meter reading, fixed taxes) separately, and calculate the per kwh cost the REAL cost you pay from your checkbook (i.e. please include all variable taxes and fees)

Tom
Apparently everyone on this message board lives in warm climates which is obvious or they’d understand the importance of the waste heat produced by the engine in a PHEV during extreme cold. But I digress. Here’s some info for those of you who aren’t familiar with it. 1. Heat pumps are effectively useless in this part of the country. The main part of the cold winters leaves them effectively useless. They simply can’t pull heat out of sub zero air. 2. Electric head is extremely common. Many small towns don’t have the luxury of natural gas or those homes were built before nat gas was cost effective compared to say propane or electric heat. I currently heat my house with propane. Beats the tar out of fuel oil (I made a funny) and since no nat gas available my other choice is electric heat. But using electric heat is sub-optimal for the environment as compared to using nat gas or propane. Your nat gas furnace (if you are able to get one) is way more efficient than any power plant…even the nat gas ones. That’s because you lose 40% approx of the electricity during transmission (I’ve seen various estimates) driving… Read more »
mx

Natural gas turbines are actually less than 50% efficient, gas to electricity.
That’s why wind farms/Battery and Solar/Battery are now providing power more cheaply.
Coal/Electric has dropped to only 30% of the utility grid.

DL

200 Amp service is the code required minimum in California now for new construction. My very small house is a coastal climate has a 200A main panel plus a separately metered 100A panel for EV charging (again, code minimum).

ziv

I have listened to ASHI home inspectors talk about heat pumps here in Northern Virginia. Some aren’t that knowledgeable but some really know their stuff. One of them had lived in Pennsylvania and his take on heat pumps was that they were useful and efficient below the Mason Dixon Line, but useless as t*** on a boar north of it. As you note, there simply isn’t enough heat in the air to draw on if the temps are below 20 degrees, or thereabouts. But even in the south heat pumps will use their resistance “emergency heat strips” from time to time.

zzzzzzzzzz

1. Not all heat pumps nowdays are the same as in your grandpa times. Some are much better in cold temperatures.

2. Even if they don’t provide full required power at any temperature, it is enough for you that they provide more heat than they use electricity most of the time, when temperature is a bit higher. Well, electric utility may not like this usage pattern, but so far it doesn’t charge extra for it.

3. As a rule of thumb, if HVAC salesman or person starts talking about “rules of thumb” to determine your heating needs instead of doing proper Reg calculations with proper non default inputs, he is moron or fraud, or both.

ItsNotAboutTheMoney

Re 1.

That’s the nub. You buy a heat pump that’s appropriate to your climate, so in a very cold climate:
– you have one that’s good to very low temperatures like -15*F
– you have back-up heating that gets used in the extremes where the heat pump would be inefficient or output would be low.

HeatPumpUser

Ignorant comment. I’ve been using a 2.5 ton, 8.5 HSPF air source heat pump for 16 years (north of the Mason Dixon Line) and it works great for our 2200 sf home. Strips only come on for short periods when the outside air temp is app. 0F or below! Literally 1-2 hours total strip use every 2-3 years. Many recent years they don’t come on at all. A modern, more efficient unit with HSPF of 12+ would obviously be even better. Read up on Quebec, as they’ve been using air source heat pumps there since the 1970s.

FWI- electric heat strips can be turned off during the heat pump defrost cycle in most all thermostats. So it blows 70 degree air for 30-90 seconds ocasioanlly, no big deal. This doesn’t lower the overall comfort of our home one bit.

HeatPumpUser

“Emergency Heat Strips.” As the name implies, for emergency use only, as in some part of the heat pump system failed. Our single stage heat pump compressor and associated heat exchangers, fans, valves, etc are still going strong after 16 years of year round use.

“Auxiliary Heat Strips.” As the name implies, to assist the heat pump in times of low system output (frigid outdoor temps.) or during defrost cycles, if desired by user.

Gasper Gartner

It may be useless if you live somewhere in Siberia, but seriously, you wrote a very long post but you didn’t mention where you live nor did you mention at what temps heat pump losses it’s usefulness.

I have a heat pump for the whole house and I can measure used electricity and produced heat. Around 0°C and 38°C water to the radiators COP is around 2.4, at average daily temps of -8°C COP was stil 1.9.

With average winter under the European Alps I get a yearly COP of 2.6. That means that my house uses up 13,000 kWh/year but it only uses 5,000 kWh electricity per year. When we were burning heating oil we using 1,500 liter at least.

I wouldn’t call that useless.

Steven

By an amazing coincidence, it’s the same temperature in suburban Philadelphia as it is in Siberia.

Guess where I live.

Tom
I just thought I’d point out some of the ignorance one this site from commenters. So far we have ignorant comments such as: 1. Electric heat? unpossible! 2. All you need is a heat pump. That’s like 1000% efficient. Uh huh. 3. Nobody lives in those places anyway. This isn’t Siberia. But these same people tend to whine and whine and whine and complain that 1. NO WAY would anyone EVER buy a Nissan until they have thermal management! To do so is just stupid! I mean it gets like 140 in the summer where I live. 2. Electric cars are 100% efficient. Why don’t you drive one? There’s no math anywhere on the globe that says it’s not best to drive BEV. The internet told me so. I don’t need thermodynamics, physics, or electrical engineering to tell me otherwise. 3. Pffftt….rooftop solar is DEFINITELY the way to go and Waaaayyyy cheaper and more efficient. All of those are abjectly false for a very large chunk of the United States not to mention other habitable places such as Europe. 1. Here’s a clue. Not everyone lives in the desert. In fact a very large chunk of people in the US… Read more »
Gasper Gartner

You wrote:
“1. Heat pumps are effectively useless in this part of the country. The main part of the cold winters leaves them effectively useless. They simply can’t pull heat out of sub zero air.”

Define the sub-zero air, is that bellow 0°C or bellow 0°F?

If bellow 0°C then I disagree, heat pump is more than useful and very effective under that conditions.

If bellow 0°F then I question how many people and how many days per year are actually living in that kind of conditions.

Bojan

Maybe he meant 0 Kelvin.

If the peak load of the house is 30kW, consider insulating it better (or, like, at all). Don’t blame heat pumps for not meeting the needs of your wasteful lifestyle.

With a house like that, an electric car won’t significantly improve your environmental footprint.

I will however agree that a Volt-like hybrid car makes sense in cold climates. Ideally, though, it would use a renewable fuel rather than gasoline.

Cecil T

I think you’re probably talking some sense here but I haven’t had the time to read your two novels.

I think the overall point is that the only way to extract energy from fossil fuels is by burning them, and the primary byproduct of that is heat. So fossil fuels become extremely efficient at heating things, that’s fundamentally what they do.

Doing anything else with fossil fuels, like transport or electricity for lighting or computers or whatever, fossil fuels are terribly inefficient, and almost any other source is generally superior.

But you’re saying in the north where it’s cold or at least not hot for half the year or more, some variant of a hybrid makes sense to utilize what would otherwise be wasted heat or excessively hard to generate in other forms. It’s a compromise between transport and heat. That’s a reasonable assessment.

Am I getting what you’re saying?

Pushmi-Pullyu
@Tom: Interesting post with lots of good info, thanks! I do have one quibble with this part of your post: “Your nat gas furnace (if you are able to get one) is way more efficient than any power plant…even the nat gas ones. That’s because you lose 40% approx of the electricity during transmission (I’ve seen various estimates) driving down the total loop efficiency to 60 % or so compared to greater than 90% for a nat gas furnace.” It’s not the actual transmission of the electricity which drops the efficiency by 40%. Transmission losses over power lines average only about 7%, at least in the mainland USA. I think what you’re referring to is the efficiency lost in burning natural gas at the power plant, which at best (for a combined cycle plant) is about 60% efficient, as you said. I’m not sure there’s much point in comparing electric heat efficiency to the efficiency of using natural gas or other fuels, as what an electric furnace does is convert all the energy to heat. In heat engines (for example, in a gasmobile’s engine) or electric motors that would count as 0% efficiency, since all the energy is lost to… Read more »
ffbj

It’s usually only in mild climates as it’s not very efficient.

Roy_H

Electric heat is the most efficient (near 100%), just not the cheapest.

DL

Heat pumps are well over 100% efficient my friend, because the MOVE heat, not generate it directly.

ffbj

Yes, but they are expensive, require lots of space, and do not do well in extremely cold climates. For milder climates they are fine.

@Roy-H Electric is never 100% because the electricity it uses is generated by burning coal or ng, or hydro, all involve loss, and further in transmission. Ng loses nothing in transmission since it is burned at the source of the heat creation, therefore it’s always more efficient than an electric furnace, unless you are creating that electricity at the source which would be like what industrial electric furnace does.
Modern gas furnaces can reach into the 90% for efficiency, but then you must add blowers motors to move the heat around. GFA.

Older gravity furnaces don’t require blowers but are only about 40% efficient.

Link

That’s only true for air based heat pumps. Using geothermal or ground water as energy source for the heat pump is very efficient even in a very cold climate.

Obviously it’s also more expensive to build, but by saving up to 75% (maybe even more) of the electricity compared to electric resistance heating it’s almost always cheaper in the long run.

David Cary

Lots of space? Since most of us (in the US in modern houses) have a/c, there is zero extra space.

Modern heat pumps do fine down to zero degrees. Most people do not consider zero degrees mild – F. Mind you, the are generally still more efficient that heat strips down to more like -10 but it gets really close.

Minn, MT, Dakotas, Maine – those would be a little cold for a heat pump. Combined they represent 5% of the US population probably? The vast majority of the US does absolutely fine with a modern heat pump.

That being said – comparing to electric “furnaces” is pretty silly. That is a heat form used in relatively few houses in the US.

The bias against heat pumps is borderline ridiculous in an EV forum. Repeats the kind of FUD that others use against EV’s.

Mikael

What is extremely cold climates for you then?
There are air source heat pumps with positive COPs down to -35 degrees.

And for cold climates you would of course do ground source heat pumps if possible.

John in AA

“Heat pumps are well over 100% efficient”

Only for colloquial (ab)use of the word “efficient”.

Pushmi-Pullyu
Thank you! I twitch every time I see someone claiming that heat pumps are “over 100% efficient”. Ummmm… no. Nothing can possibly be more than 100% energy efficient, by definition. What heat pumps do is move existing heat around, and in the process of moving that heat can (and usually do) use less energy than the energy contained in the heat that is moved. Now, I have read enough to know that people who sell and install heat pumps do blithely talk about them being “more than 100% efficient”, but all they’re doing is demonstrating their lack of understanding of thermodynamics. BTW there is one type of heat pump system which actually is adequate even in regions where it gets really cold in the winter: Ground source heat pump systems, also misleadingly labeled “geothermal heat pump” systems. They use loops of pipes buried deep underground, “ground loops”, buried deep enough that the ground temperature is stable year-round. However, that kind of system is a lot more expensive than a normal home heat pump HVAC system. But those building a new home should really look into that. According to the Wikipedia article: “Setup costs are higher than for conventional systems, but… Read more »
John in AA

I’m told air-source has gotten a lot better since I formed my bad opinion of it — good enough for year-round use in Michigan — but I’m not currently motivated to investigate further.

John in AA

And yes, if I were building new I’d install geothermal. Probably with radiant heating in the floor.

mx

If it’s built into a zero-energy home, it’s the best choice.
No exhaust from heat production, no air intake, no exhaust venting.
That’s why there should be a US push for Zero Energy Homes.
These homes have almost 90% less heat demand in the first place.

philip d

One thing they don’t cover is duration of this power use. So on a hot summer day your AC might be using 3-4 kW nonstop over a 12 hour period or intermittently equaling a total of 12 hours over a 24 hour period. A car charging will use maybe 7 kW over a 4 hour period on average for daily charging.

So if everyone is running their AC at the same time there is more power being loaded on the grid than when people are charging their cars at random times and for only around 4 hours at a time. Even though car charging has a larger load it is for a shorter duration and will have less overlap with other people charging.

zzzzzzzzzz

Heat pumps typically have resistance heat strips as backup. 5-10 kW. As temperature gets lowest before dawn and head pump power is reduced and can’t cope, both heat strips and heat pump may operate together.

Using words like “typically” or “average” in this context sounds very fishy though. It is peak load during cold spell that matters. Either grid has enough diesel (yes diesel) and nat. gas gensets/turbines, and transformer power to supply everybody, or not.

Steven

Welcome to the suburbs of Philadelphia, where many developments are electric only.

If you want gas, it will be propane, and you’ll have a tank or two on the side of your house. If you want oil, same thing.

Sorry, but PGW (Philadelphia Gas Works) doesn’t come out this way, unless you’re willing to pay for the feeder all the way back to the main.

L'amata

Believe it or not. If a home is well insulated, and electricity is cheap, electric furnaces can be pretty efficient since they have No Chimney & there is Zer0 heat loss.

DL

A heat pump is still the better choice.

Bojan

In extremely well insulated houses, a case could be made that the energy savings from using a heat pump over an electric heater would be insufficient to cover the larger cost of a heat pump.

However, space heating is not everything. Hot water use is independent of how well a house is insulated and in very well insulated houses, heating water uses up more energy than heating the house. Because of that, I would agree with you in recommending a heat pump for well insulated houses, too.

David Cary

Have to call out the misuse of the word efficiency.

Cost effective – sure.

Chimney losses on a modern NG system – ha!

MM
Good article for perspective, and for the realistic wiring demands for an electric car. Most of our people are less than 100 miles away, during a short visit, I ask them if they have a wall plug close by for me, I describe the load as a 1500 trickle charger, equivalent to a smaller plug-in heater. They have a couple of DCFC’s close by, I charge to 85%, drive a couple of miles to my destination and it does the slow finish to 100% without me having to wait for it. Our house went all electric, our biggest demand does come from our car, but only because we modernized all of our appliances and insulated our home. With our solar panels dashboard it describes exactly our energy use, our mini-split heat pump has never drawn more than 1700 watts in the coldest of winters to heat a 2,000 sq ft home. Overall, how much power used to charge a car depends on where you went with it, our 40 mile commute ended, we now really only need to charge once or twice a week, we’re lucky to have a fast charger installation finishing up close by our grocery store, it… Read more »
MM

“Around here” Seattle.

EV-A

This “limitation” is outdated. There are great solutions on the market for that.

I’m using an energy manager (example: https://maxem.io/en/) for exactly that purpose, so I’m always getting the maximum available energy from solar and/or grid, without having to worry about the fuses.

Roy_H

Typical clothes dryer about 5500W, stove with all burners & oven about 7500W.

Sch

+1

ItsNotAboutTheMoney

Yes. We have oil heat still* so our biggest loads are our electric stove and the dryer.
Our Volt is nothing. Even if/when I replace the Prius with a BEV just a bit of smarts with charging should keep our peak down.

* will need to be replaced; want to have heat pump plus fuel back-up

mike w

Good idea. I lived in Pittsburgh for a while. My house was dual fuel. Heat pump for mild weather and a outside thermostat automatically switched to gas heat when the temperatures got too low for the pump.
But this raises a good point. No matter where you live you still have a spring and fall season so heat pumps can provide very economical heating during those season.

Bojan

Having two heating sources increases your initial investment, though. In modern, well insulated houses, the savings on running costs from having two systems likely won’t cover the extra investment.

Bill Howland

Yeah looks to me like the only reasonable way to use any substantial amount of electric heat is to use the ‘cold weather’ Mitsubishi heat pump systems, which, although not Energy Star rated due to mediocre hot weather efficiency, in cold climates such as mine here in western NY state, those units are the only products that can compete with low Natural Gas rates.

Saying resistance electric heat is 100% efficient is rather the same issue as saying an electric car is 98% efficient. Has no real relation to practicality.

My home is quite substantially insulated with good window seals, and more than adequate insulation, yet resistance electric heat would be quite a burden to pay for.

I’d certainly hope Ev’s cost less to recharge.

David Cary

“more than adequate insulation” – you probably need to rethink that.

I know of people who build in IA – much colder than you – and get electric resistance down to $30 a month.

Your electric rate is probably a bit high so NG is generally a good financial choice but realize that NG is always dirty and electric isn’t. So much hydro near you that is infinitely cleaner than fracking.

Bill Howland

David Cary how could you possibly know what you’re talking about. My gas bill last month was $56. And that is with 8 gas appliances in a 2200 sq ft house. Unlike John Doe I do not pay $2000 year for electricity. I pay $188.04 and that is ENTIRELY billing charges – or less depending on whether I have made MORE than 100% of my usage in Solar. The first year I had the solar system I made 300 % of my usage so in future years I took steps to minimize the overage, since it just ends up being a windfall for the utility.

$30 a month which you claim in Iowa doesn’t float around here since that would only allow $112 for usage, or less than 90 kwh per month on average… My weather is colder than Iowa’s.

vdiv

Random datapoints. The yesterday I drove around quite a bit and the car used 40kWh to recharge overnight. That same day (24h) my home HVAC used 33kWh for the two stage heat pump and 34kWh for the 10kW resistive heater, some was certainly used for defrosting the heat pump.

It was freaking cold, -13°C to -7°C with 15-20 km/h wind.

Sch

But remember when our friends from USA are talking about sub-zero temperatures, they mean sub 0 degree Fahrenheit, which is -18 degree Celsius.

I had a Chevrolet Volt and drove 10.5 miles each way to work and the car only used 5.5kw per day in the winter the heater drew another 1/3, my 40gal electric heater used more power, ~ $40 per month where the volt was around $22 at N VA dates.

guyinacar

So one PHEV consumes less than six hand-held hair dryers. Got it. And one Frisbee is shorter than six billiard balls. Not sure what any of that proves. But, hey, our tax dollars at work.

Now, if you nice DoE regulators would like to do something truly bold and useful (something on which the mocha-latte, Greenpeace brake-for-whales crowd and the long-gun, MRE survivalists might all agree), how about laying down a safe DoE national standard for grid-tie two-way EVSEs with proper grounding? Then we can charge our (x)EVs when the grid is up, or heat/cool the house when the grid is down. Like, we can do it for for days.

Better yet, DoE, why not smash some skulls together and make the NEC, the ISO grid(s), the local utilities, and all the car companies agree that there shall be a clear and singular standard, to be promulgated across industries, and without NFPA copyright? How about that?

Put some teeth in it this time.

Bill Howland

Since most VOlt owners charge at the 1.45 kw rate, and MOST hair dryers for sale in North America draw 1.5 kw, this means that – not 6 or 7 hair dryers – most VOLTS out there recharge at less strain to the wiring that one hair dryer does. Of course the VOLT is plugged in a bit longer.

Doug Bostrom

We don’t drive a heck of a lot (well actually it’s ~30 miles per day if I do the math) but even so I’ve been surprised to find the recharging cost of our vehicle to be essentially unnoticeable when buried in the monthly bill. We deep-sixed a final swath of ~40 incandescent bulbs that were typically in use for a few hours per day at roughly the same time as purchasing the car so perhaps it came out as a wash. In any case, there was certainly no dramatic increase in our bill.

SteveSeattle

What kW power rating is really necessary from your home charging station?
My Volt draws about 3.5 kW for 4 hours and that is enough to replenish all the energy I need to do a 40 mile commute. Do I really need a higher power EVSE even if my future car can charge at 10kW?

Bojan

Very much agreed. Home charging does not need such high power outputs. Just because the car’s charger can take it doesn’t mean you need to supply that much power. The car will be sitting there for the whole night while you sleep, so it’ll has plenty of time to trickle charge and you can save yourself the expense of upgrading your power connection.

Alaa

10 kW for a furnace is way too much. A heat pump will be max 3 kW.

Here is a link to a heat pump that will take 2.6 kW of electricity and produce 12 kW of heat, thus a coefficient of performance of 4.5

https://mobi.renewableenergyhub.co.uk/uploads/products/17699/product_brochures/EHS_IDU_and_ODU_Mono_for_Europe_50Hz_Ver1_4_TDB.pdf

HeatPumpUser

Definitely a USA/Canada specific statistic for 10 kW electric resistance heat strips in air handler (ducted heat/AC). Our heat strips are 5 kW and 10 kW in two stages- 5 kW or 15 kW, depending on need. Strips almost never come on, as air source heat pump takes care of heating needs 99.9% of time.

Even more ridiculous are instant hot water strips designed for the whole house and to replace a hot water tank. 25-35 kW. Take that electric grid!

HeatPumpUser

I have a standard 50 gallon, 5 kW electric water tank inside home. My neighbor has 30 kW instant electric hot water strips, which was installed when old tank leaked. Tank may have leaked due to his use of water softener that quickly destroys the sacrificial rod that protects painted steel in tank from corrosion.

John Doe
I live in Norway, and the main (and in reality only) source of heat is electric. I have a heatpump unit that contains two water tanks. One for tap water, and the other for floor heating. The unit contains a fan unit for the ventilation system, that is also where the heat pump unit is located. It takes hot air, that is on its way out of the building, and “recycle” the heat. If the air going out to the heat pump unit is 25 degrees C, it is 4-7 degrees C when the heat pump has done its job. That heat in converted to hot water in the two tanks. The two tanks also include a regular electric heating element, but that has not been used ever. No need, since the unit works so well. I also chose to have some radiators in the house, that is connected to the same system. If you choose you can connect solar heating (from the roof) to this system. If you have a wood or pellets over with a water heating unit – that can also be connected to the system. My system is not very advanced, and I can regulate how… Read more »
(⌐■_■) Trollnonymous

I have a Juicebox 60a and I charge at 40a continuous……….ok, 39a really.