Impact of heat or air on range of electric cars?

When you turn on the heat on a gasoline driven car, it just uses the heat of the engine. Air conditioning reduces the mileage a bit for sure. But an electric vehicle must use the battery both to heat and cool. Does this reduce the range–already a problem–significantly?

Here’s a thoughtful post on owning a Tesla Model S for a year. The owner lives in New York State, and reports that in winter, cold weather increases power consumption - and thus presumably decreases range - by around 30%. It’s a combination of passenger heat and the need to heat up the batteries - which means it’s a worse problem for short trips (which are the ones where you don’t care about range as much).

He also notes that when it’s cold, Tesla software “emasculates” his two favorite features: strong, smooth acceleration and regenerative braking. But he still loves the car.

As for A/C, various Googling suggests this costs around 3 kw, which represents roughly a 15% increase in power consumption.


Some of the early electrics used a separate fueled heater. Not sure what the fuel was, but it wasn’t gasoline in the one I was told about. I don’t know exactly what the hybrids do, I assume they can run the engine to produce heat, and charge batteries, but it’s a different situation from a fully electric car.

Ref Xema’s numbers …

Since most people run either the AC or the heater most of the time in most of the country in most cars, electric or IC, perhaps we should stop thinking of those gizmos as accessories or frills and instead start treating them as simply, like rolling friction or transmission losses, part and parcel of operating a car.

Said another way, an IC car gets a 5-10% mileage boost in winter when the AC is off and the heat is free compared to the baseline case when the AC is on. This boost is offset by crappy gas mileage with cold engines, ethanol additives, and general snow-induced traffic, more driving in the dark with more lights on, etc.

An EV gets X mileage in the warm part of the year and 15% less mileage in the winter with the non-free heater running in lieu of the non-free AC. But it doesn’t suffer from cold engines nor ethanol additives. Though it still suffers from snow-induced traffic and short days with long nights just as the IC cars do.

Comparing electric and IC cars is always tricky. Sticking to electric, the battery is simply going to store and discharge less electricity when it’s cold. This is the biggest effect AIUI, and how you can get results like range dropping by 50% or more in some cases, far more than the effect on IC cars. But you aren’t necessarily losing efficiency in energy per mile terms by that cause, just as you aren’t really losing efficiency in energy per mile terms an IC car if winter gasoline has fewer BTU’s per gallon, though losing in $ per mile terms if the gas costs the same. Also back to EV it’s relatively less efficient to generate electricity in a central station, send it through the grid etc just to use it for heat (your car’s heater) than it is to use that same set up to generate mechanical power, so the more the car is a rolling resistance heater the less relatively efficient in principal compared to a car which burns fuel locally.

But there are so many variables between IC and EV to be nitpicking about the heater.

Another item which affects both not so far mentioned is air density, which can be a noticeable effect in highway driving with no snow on the ground or difference in traffic pattern. It’s hard in IC case though to separate from gas energy content if you’re measuring. Another small offsetting one is turbocharged cars’ (more than naturally aspirated ones) slightly better engine efficiency with colder intake air.

Not only do electric cars not have the “cold engine” problem in winter, at least Teslas stay warm when they’re charging, so you don’t have to warm the cabin up at the start of your drive. I think they even try to keep the batteries warm by using some of the electricity. Apparently it uses less power to warm the batteries than it would to let them get cold and lose capacity.

As others have mentioned, there’s a lot of factors that go into summer vs winter performance of IC cars too. Summer vs winter gas is one, as summer gas doesn’t give as good mileage but it reduces ozone and smog pollution that forms in the hot summer sun. An IC engine runs more efficiently with colder air because it’s denser, allowing greater volumetric efficiency of the engine. This is counteracted by increased wind resistance on the vehicle itself though (slow driving would be more efficient in winter than summer, but highway driving would be more efficient in summer, though I have no idea where the speed and temperature crossover point is). Longer warm-up time in winter, which means the engine runs a much richer mixture and also idles at higher RPMs, kills efficiency, even though you’re not using the a/c. Ignoring summer vs winter gas, I tend to get the best mileage out of my car in the spring and fall when the engine doesn’t need to warm up too long, but I don’t need to run the a/c either. Then there’s the whole windows-up vs windows-down situation. :slight_smile:

Speaking as the owner of a 2012 Mitsubishi i-Miev electric vehicle, running the heater or the A/C tends to reduce range by roughly 10-15%.

The i-Miev has a range meter right on the dashboard, showing estimated miles remaining. You can watch it change when you switch the climate controls on and off. Suppose you’re driving home and the range meter says 42 miles but you know that you’re 30 miles from home so you figure you’ve got 12 miles to spare. Now you switch on the A/C and oops the range meter suddenly drops to 36. So there goes half of your margin. In three years of driving the EV, there have been a handful of times when I had to turn off the climate controls in order to extend the range of the vehicle.

But speed has a bigger effect on range than climate controls does. At 60 mph, you’ll only get half the range that you’d get going 30 mph. Also, start-and-go traffic will eat into the range more than slow-and-steady driving will.

95% of the time, I don’t even worry about it. I rarely go more than 10 miles from home and the car has an emergency reserve of about 10 miles after you hit “E”. It’s not a big deal for me.

You can, of course, do exactly this with your gas/diesel vehicle, by plugging in an engine block heater.

And it’s striking how good gas engines now are at starting when cold. It’s been many years since one of mine took more than a few seconds to start in any temperature above -15 F.

Yes but those are uncommon anywhere but the far north, especially for gasoline vehicles (they’re more necessary for diesel), and they’re an extra expense. Keeping the vehicle parked in even a moderately conditioned garage helps too, at which point you wouldn’t need a block heater, but if you do need one and you’re parked outside you’re unlikely to have anywhere to plug it in.

And yes, while it’s not difficult to start a car in the cold nowadays, it still runs rich for quite a while, and today’s more efficient engines take longer to warm up. Unfortunately it’s very difficult to research any statistics for that because pretty much all the search results turn up articles about idling your car to warm it up (which overall you shouldn’t), and that’s a lot of chaff to sift through.

I have a unheated but insulated garage, built about 10 years ago. Even when it’s 0F out, or even -30C, the biggest problem is the big puddle that forms under the cars from melted snow from the wheel wells. I have to dig out the shop vac and empty out about 2 or 3 loads of water.

I have a newer BMW. Even in the showroom they plug them in; it even came with a power cord. there’s so much electronics, with GPS, computer, remote assistance, fancy entertainment system, alarm, etc. - that leaving it sit for an extended period (weeks) can kill the battery. I have experienced the situation where leaving the vehicle on the street at -20C all day means when I get in, it warns me about low battery due to combination of extremely col battery and drain during the day. It says assorted “optional” electronic functions have been turned off. Once I’ve been driving a while and the battery warm up, all is good. My wife’s hybrid Camry has never hinted at a battery temperature problem in the same situation. I suspect the insulated garage is the handiest part of this arrangement. Of course, a hybrid has the best of both worlds - heat and spare power.

There was a newspaper article by I believe a New York Times reporter testing an early Tesla who ended up being towed in the winter because of these battery, heater issues and a resulting significant cut in the range of the vehicle.

Volt owner here: During the most extreme weather, I’ve lost about 20% of my battery range. Most days though I’m above 95% efficiency. It should be noted that ICE cars also lose range during cold weather.

This is a particular problem with newer (IC engine) BMW’s, not that it’s totally absent in other makes but you hear about it alot with BMW’s. Happened to ours too, where it turned out eventually to be (or cause?) a battery and ‘smart battery cable’ problem. Fortunately they replaced both under warranty, sometimes dealers give a hard time about short life batteries. But no cold weather since then.

It’s apparently that the arrangement of charging the battery partly from regenerative braking energy (yes on a regular IC car, not a hybrid) is so fine tuned to optimize energy use the car is marginal at charging its own battery by normal working of the alternator on trips less than a couple of hours. And it almost always leaves the battery less than fully charged to have room for energy gathered regeneratively. Our problem started in the winter season but then the big draw downs of the battery might have hastened its demise. Or maybe the ‘intelligent battery cable’ was always defective, or a weird accident we had* damaged one or both. Anyway Bimmer forums are full of stories of the same general problem.

*the automated garage we park in somehow popped the car’s trunk, which then got caught in the mechanism, fortunately insured, but battery is in the trunk and the problem coincidentally or not started not long after, the car’s second winter, first winter no problem. Now use the trunk disengage switch. :slight_smile: It’s a great car overall though, excites my IC Luddite side and I’d never turn it in for an electric (I know a Tesla S could beat its ass in a straight line, don’t care, no interest).

He also found that failing to charge it, going on impulse drives off his scheduled path, and ignoring the alerts on remaining battery life were problematic as well.

In some cases it can be quite substantial as well. I use my car for primarily driving back and forth to work and while I can get roughly 550 km on a tank in the summer, I rarely get more than 350-400 in the winter. That’s with a heated garage and plugged in at work so minimal warm up. I should point out that N.Alberta gets pretty chilly in the winter, though.