Heater
An ICE heats the cabin with free waste heat; an EV has to spend battery energy to stay warm.
By Anthony LimpertASE Master Automobile Technician- Early EVs used resistive heaters (huge energy draw). Modern EVs increasingly use heat pumps (2-3x more efficient), leveraging the A/C circuit.
How a given EV makes cabin heat directly affects its winter range, and heater technology is one of the biggest efficiency differences between EV generations.
Resistive, PTC, and Heat Pump Systems
EV cabin heat comes from three technologies. The earliest EVs used simple resistive heaters — essentially a big electric element — which work fine but draw enormous power straight from the traction pack. PTC (positive temperature coefficient) heaters are the refined version of resistive heating, self-regulating and quick, but still converting battery energy to heat at roughly one-to-one.
Modern EVs increasingly use heat pumps, which run the air conditioning circuit in reverse to move heat from outside air into the cabin. Because a heat pump moves heat rather than generating it, it delivers roughly two to three times more heat per watt than resistive heating — a huge win for winter range. Many heat pump vehicles retain a PTC element as backup for extreme cold, when heat pump efficiency falls off. When diagnosing an EV heating complaint, identify which architecture you have first; a heat pump system is refrigeration diagnosis, while a PTC failure is electrical.
| Technology | Efficiency (COP) | Typical draw | Notes |
|---|---|---|---|
| Resistive element | ~1.0 | 3-7 kW | Earliest EVs; simple, power-hungry |
| PTC heater | ~1.0 (self-regulating) | 3-7 kW | Refined resistive; fast heat, same range cost |
| Heat pump | ~2-3 above roughly 15-20°F | A fraction of resistive draw | Moves heat instead of making it; efficiency falls in extreme cold |
| Heat pump + PTC backup | Best of both | PTC engages in extreme cold | Common modern architecture |
| Range impact of heating | Roughly 10-30%+ in winter | Heat pump cars lose noticeably less | Driver behavior (seat heat vs cabin heat) matters |
Draw and COP figures are generic — verify architecture and specs per model. Identify which system the vehicle has before diagnosing any heating complaint.
- Identify the heating architecture first — PTC, heat pump, or hybrid of both. This one fact decides whether you are doing electrical diagnosis or refrigeration diagnosis.
- For PTC systems: verify HV supply to the heater, commanded duty versus actual current draw, and interlock integrity. A commanded heater drawing no current is a failed element or open HV feed — and it is an HV component, so de-energize before touching it.
- For heat pump systems: this is refrigeration work — pressures, valve operation, refrigerant charge. Check mode-switching valves in particular; a valve that will not reverse strands the system in A/C mode.
- Check for a coolant-loop cabin heater layout: some EVs heat a liquid loop that feeds a conventional heater core, so a failed circulation pump or airlock presents as no heat with a healthy heater.
- Scan HVAC DTCs and actuator data throughout — blend door and mode actuator faults mimic heater failures on every architecture.
- Running refrigeration diagnostics on a PTC car — or electrical diagnostics on a heat pump car. The architectures fail completely differently, and the wrong diagnostic tree wastes the whole visit.
- Forgetting the cabin heater is a high-voltage component. PTC heaters run on pack voltage; opening the circuit without de-energizing is an HV safety violation, not an HVAC shortcut.
- Dismissing a winter range complaint without asking about heater use. A resistive heater at full blast can be the single largest load on the pack — the 'range problem' may be a heating-habits conversation.
Why does a heat pump deliver two to three times more cabin heat per watt than a PTC element?
Because it moves existing heat rather than generating it. The reversed refrigeration cycle pumps heat from outside air into the cabin, so the electrical energy spent runs the compressor rather than becoming the heat itself. A PTC element converts energy to heat at roughly one-to-one; the heat pump leverages each watt into multiple watts of moved heat — until extreme cold shrinks the available outdoor heat and efficiency falls.
A heat pump EV heats fine at 35°F but blows lukewarm at -5°F while a PTC-equipped car heats fine at both. Is the heat pump car broken?
Probably not — heat pump efficiency collapses in extreme cold because there is little outdoor heat to move. That is exactly why many designs carry a PTC backup element for deep cold. The real diagnostic question is whether the backup PTC is engaging; if the car has one and it is not stepping in at low temperature, that backup circuit is your fault to find.
Why does a heat pump deliver two to three times more cabin heat per watt than a PTC element?
Missed one? The reasoning above comes straight from the EVH exam bank, so this is the standard you will be held to.