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How do older Model 3s generate cabin heat?

srs5694

Active Member
Jan 15, 2019
1,544
2,067
Woonsocket, RI
When I bought my Model 3 in early 2019, many reviews and general discussions claimed that the Model 3 relied on a novel method of generating cabin heat: The claim was that they scavenged waste heat from the electronics and motors; and if more heat was needed than would normally be generated, the car would run the motors in a deliberately inefficient manner so as to produce more heat. The claim was that this method of generating heat was more efficient than using resistive heaters, which many other EVs used, although it was less efficient than heat pumps, which a few EVs used.

Once Tesla added heat pumps to the Model 3 (and Model Y, which has always shipped with a heat pump, IIRC), the claim about older models suddenly changed. Online discussions and auto reviews suddenly claimed that the older Model 3 had been using resistive heaters all along. References to heat scavenging dried up.

I've never seen any discussion about why these claims so suddenly changed, and now I'm wondering which claim was true: Does my 2019 Model 3 use resistive heaters, does it use a heat-scavenging system, or does it use both? Also, if it uses heat scavenging, how efficient is that compared to resistive heaters and heat pumps?

I'm curious about this because I've gotten questions about how EVs generate heat at EV events, and with National Drive Electric week coming up, I'd like to have my facts straight.
 

Tam

Well-Known Member
Nov 25, 2012
11,828
10,863
Visalia, CA
When I bought my Model 3 in early 2019, many reviews and general discussions claimed that the Model 3 relied on a novel method of generating cabin heat: The claim was that they scavenged waste heat from the electronics and motors; and if more heat was needed than would normally be generated, the car would run the motors in a deliberately inefficient manner so as to produce more heat. The claim was that this method of generating heat was more efficient than using resistive heaters, which many other EVs used, although it was less efficient than heat pumps, which a few EVs used.

Once Tesla added heat pumps to the Model 3 (and Model Y, which has always shipped with a heat pump, IIRC), the claim about older models suddenly changed. Online discussions and auto reviews suddenly claimed that the older Model 3 had been using resistive heaters all along. References to heat scavenging dried up.

I've never seen any discussion about why these claims so suddenly changed, and now I'm wondering which claim was true: Does my 2019 Model 3 use resistive heaters, does it use a heat-scavenging system, or does it use both? Also, if it uses heat scavenging, how efficient is that compared to resistive heaters and heat pumps?

I'm curious about this because I've gotten questions about how EVs generate heat at EV events, and with National Drive Electric week coming up, I'd like to have my facts straight.

Before the Model Y, all Tesla were using resistive heaters. Of course, they could use waste heat from the drive unit, battery... but in winter, I doubt there's enough "waste" heat from those components to heat your cabin. Thus, the cabin needed resistive heaters and now the heat pump.


cabin-heating-slide-1-gb.jpg
 
Last edited:

stopcrazypp

Well-Known Member
Dec 8, 2007
13,044
9,339
When I bought my Model 3 in early 2019, many reviews and general discussions claimed that the Model 3 relied on a novel method of generating cabin heat: The claim was that they scavenged waste heat from the electronics and motors; and if more heat was needed than would normally be generated, the car would run the motors in a deliberately inefficient manner so as to produce more heat. The claim was that this method of generating heat was more efficient than using resistive heaters, which many other EVs used, although it was less efficient than heat pumps, which a few EVs used.

Once Tesla added heat pumps to the Model 3 (and Model Y, which has always shipped with a heat pump, IIRC), the claim about older models suddenly changed. Online discussions and auto reviews suddenly claimed that the older Model 3 had been using resistive heaters all along. References to heat scavenging dried up.

I've never seen any discussion about why these claims so suddenly changed, and now I'm wondering which claim was true: Does my 2019 Model 3 use resistive heaters, does it use a heat-scavenging system, or does it use both? Also, if it uses heat scavenging, how efficient is that compared to resistive heaters and heat pumps?

I'm curious about this because I've gotten questions about how EVs generate heat at EV events, and with National Drive Electric week coming up, I'd like to have my facts straight.
I think people misunderstood how it uses heat from motors and electronics to heat the battery, not to heat the cabin.
Here's a patent related to that:
Tesla New Patent To Use Electric Motor Waste Heat Mode To Heat Battery

The older Model 3 had no way to put heat from those sources into the cabin.
 
When I bought my Model 3 in early 2019, many reviews and general discussions claimed that the Model 3 relied on a novel method of generating cabin heat: The claim was that they scavenged waste heat from the electronics and motors; and if more heat was needed than would normally be generated, the car would run the motors in a deliberately inefficient manner so as to produce more heat. The claim was that this method of generating heat was more efficient than using resistive heaters, which many other EVs used, although it was less efficient than heat pumps, which a few EVs used.
I’m pretty sure this is in reference to heating the battery since unlike the S/X of the time and other EVs, there is no dedicated battery heater. The cabin heater was a resistive heater as far as I’m aware.
 
in early 2019, many reviews and general discussions claimed that the Model 3 relied on a novel method of generating cabin heat: The claim was that they scavenged waste heat from the electronics and motors; and if more heat was needed than would normally be generated, the car would run the motors in a deliberately inefficient manner so as to produce more heat.

That's how the battery was and is heated, not the cabin.

The cabin was always heated via resistive heater (and seat heaters.)

(I have a 2018.)
 

STS-134

Active Member
Aug 8, 2021
1,455
2,322
SF Bay Area
Old Model 3 thermal management system:


New Model 3 (and all Model Y) thermal management system:




BTW, I suspect that this isn't an entirely exhaustive list of operating modes. I suspect that if it's really hot outside, the liquid cooled condenser, radiator, and drive unit are kept in one loop, and reject heat to the atmosphere, and the battery + chiller are kept in another loop to keep the battery cool, and the cabin evaporator removes heat from the cabin. This way, relatively hot glycol coming from the radiator will not be fed directly to the chiller which would not be efficient because the compressor then has to pump all of that heat back to the liquid cooled condenser.
 
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