A better environment with electrical preheating

- International studies show benefits from electrical preheating for air quality and the environment.

An increasing number of international studies reveal that cold starts is the main cause of harmful emissions from cars. This is true even for the newest cars on the market. These emissions contribute poor air quality in the cities, which in turn impact the health of everyone living there. The good news is that the same studies show that electrical preheating is an effective tool in combating cold starts and it’s effects.

One recent study on the effect of cold starts, performed by researchers at Berkeley, Carnegie Mellon, University of California and MIT, show that modern petrol cars release the same amount of harmful emissions in the first 30 seconds after a cold start as in 300 kilometers of driving with a warm engine.

Another test, performed by VTT – the independent state research institute of Finland, found that electrical preheating can reduce harmful emissions by as much as 71% in sufficiently cold conditions.

See reports:

Furthermore, the Swedish Road and Transport Research Institute (VTI) concludes that significant cuts in emissions can be achieved through increased use of electrical preheating.

The consensus is the same in Norway, where both the Institute of Transport Economics (tøi) and the Norwegian Automobile Association (NAF) recommends the use of electrical preheating to lower emissions.

What is a cold start:

Whenever an engine is started temperatures below +10 centigrade without prior heating, it is considered a cold start. Under these conditions emissions will always be elevated, but they become progressively higher as temperatures get lower. A cold started engine will emit considerably more at -10 degrees than at +10 degrees.

Car on winter road

How cold starts lead to increased emissions:

To understand why the impact of cold starts is so great, one must first understand its effects.The total increase in emissions after a cold start is a result of several factors. All of these factors play an increasing role as the temperature gets lower.

  • Cold makes the oil too viscous. The lack of proper lubrication leads to increased friction, and a less efficient engine. This in turn leads to increased fuel consumption and emissions.
  • A cold engine is supplied with more fuel by design. This elevated consumption is maintained until the engine reaches optimal operating temperature.
  • The catalyst must be warm to function properly. The catalyst removes harmful particles and gases from the exhaust, but it only works properly once it has been heated by the exhaust. The increased infusion of fuel into a cold engine is partly designed to heat the catalyst more quickly.
  • The battery is drained in the cold and is recharged through additional fuel consumption. If the battery is not adequately charged before you start driving, it needs to be recharged by the generator. Since the generator is run by burning extra fuel in the engine, this naturally leads to increased emissions. With cold weather, short drives, frequent use of comfort functions like defrosters, seat heaters and fuel heaters, the batteries in many cars are continuously being drained and never fully recharged. With the generator running continuously, emissions increase.

How electrical preheating lowers emissions:

An electrical preheating system consists of an engine heater, an interior heater, a battery charger and app control, all of which contribute to lowering emissions.

The engine heater heats up the engine and motor oil, ensuring that the engine is well lubricated, leading to reduced friction and optimal efficiency.

The interior heater raises the temperature in the cabin to a comfortable level. This melts the ice and snow of the windows and reduces the need for power hungry comfort functions like defrosters, seat heaters and fuel heaters.

The battery charger ensures that the battery is always charged before you start driving. In combination with the reduced use of comfort functions, this means that the battery requires less charging during driving. Less fuel used to run the generator means lowered emissions.

The app control system helps you make sure that no excess energy is used to heat the car. The user can easily program the system to heat the car in time for regular departure times. The system automatically determines when to start heating based on the outside temperature.

Massive reductions with electrical preheating:

In the test performed by VTT in Finland, regular Euro 5 petrol og Euro 6 diesel cars were tested against identical models outfitted with DEFA’s electrical preheating system WarmUp. The test considered the first 20 minutes of driving after a cold start at -20 degrees. Some important findings are presented below:

Petrol EURO 5 Co2 (g/km) PM (mg/km) NOx (g/km)
Cold start 306 152 0,35
Preheated 253 12 0,17
Reduction 17% 92% 52%


DIESEL EURO 6 Co2 (g/km) PM (mg/km) NOx (g/km)
Cold start 254 <1 0,97
Preheated 198 <1 0,60
Reduction 22% 0% 38%

Key findings:

  • Electrical preheating can reduce the emissions of PM from petrol cars by up to 92%. PM is very harmful to health and a primary driver of poor air quality in the cities.
  • Electrical preheating can reduce the emissions of NOx from petrol cars by up to 52% and from diesel cars by up to 38%. Even though the percentagewise decrease is larges for petrol cars, the effect in g/km will be larger for diesel cars (-37 g/km vs. -18 g/km), since they emit more NOx. .
  • Electrical preheating can reduce emissions of Co2 from petrol cars by up to 17% and from diesel cars by up to 22%. The effect will be slightly larger for diesel cars, even though they emit less Co2 (-56 g/km for diesel vs. -53 g/km for petrol).
  • In addition, emissions of HC and CO are almost entirely eliminated by preheating.

All in all, the test shows that electrical preheating can reduce the total amount of harmful emissions by up to 71% and fuel consumption by up to 24% under the conditions tested.

Massive reductions in emissions are possible:

At the last count performed by Statistics Norway (SSB), there were 2,6 million private cars in Norway. 47,6% of these were diesel cars, 49,7% were petrol cars and only 2,7% were low or zero emission cars. In addition, there were 450 000 vans and small trucks,  92% of which were diesel powered. The average age of Norwegian cars was 10,5 years, higher than the average in countries like Greece, Romania and Hungary. As much as 22% of the cars were 15 years old or more. Older cars on average emit more than newer cars.

However, new cars also emit more than we would like to think. In 2015 the Institute of Transport Economics in Norway released a report titled Emissions from new vehicles – do they keep what they promise?

The report reveals that Euro 6 approved diesel cars emit 4 to 20 times as much NOx during city driving than the requirements for the type approval. The report also reveals that emissions from these vehicles on average are 4 times higher than the average for busses and heavy trucks with Euro VI og Euro 6 diesel engines.

These numbers make abundantly clear that more measures have to be taken to reduce the emissions of NOx and NO2 from private cars. Increased use of electrical preheating would have a large positive impact on air quality and public heath in urban areas.