Monday, October 1, 2012

“Hello, iStove”: How much can lambda sensor technology improve burning efficiency?

Lambda sensor system (Reprinted from

The introduction of innovative emissions control technology revolutionized the automobile industry, making cars safer, greener, and more efficient. Now, some boiler manufacturers are saying goodbye to the clunky, soot-filled burners of the past, and are integrating the same lambda sensor devices used in automobile engines into new state-of-the-art clean-burning wood boiler. Economical and carbon-neutral, these eco-friendly lambda heaters could help make wood-burning cool again. Goodbye low efficiency – Hello, iStove.

What is a lambda sensor?
A lambda sensor is a small electronic device that measures how much oxygen is in a gas or liquid. Lambda sensors have been used in a variety of applications since their development in the 1960s – from monitoring breathing in scuba diving to measuring soil oxygen content – but they are most well-known for their use in car emissions control technology. Lambda sensors help cars optimize the fuel combustion process, allowing engines to work as efficiently as possible with the least emissions. In lambda wood heaters, the sensors are used in a similar way to reduce fuel waste and minimize emissions during burning.

How does lambda sensor control work? 

Lambda sensors are key components in the feedback control systems that regulate combustion. Like car engines, wood stoves burn fuel (biomass) in the presence of oxygen. The ratio of air to biomass fuel (“air-to-fuel ratio”) in the stove’s combustion chamber determines how efficient the burning will be. If there is too much air in the chamber, burning will produce high levels of noxious nitrous oxide pollutants. If there is too little air, combustion will be incomplete and the stove will release wasted fuel in the form of hydrocarbon particulates and harmful carbon monoxide gas.

Feedback control fine-tunes the combustion process by varying the air-to-fuel ratio in the chamber so that burning is optimized. A lambda sensor measures the oxygen concentration of the exhaust stream leaving the stove (a measure of how much excess air is in the combustion chamber) and sends the information to a controller or micro-processor, usually as a voltage signal. The controller calculates the current air-to-fuel ratio and varies the amount of air fed into the chamber based on the real-time data from the sensor. These two components working together keep the stove running continuously at near-optimum efficiency, regardless of the species and moisture content of the fuel wood or the boiler temperature.

Lambda boiler manufacturers
Lambda boilers have been on the market since the 1980s, but in recent years more companies are focusing on the residential market and have released newer models featuring upgraded technology and a cleaner aesthetic, including British manufacturers Pevex and Attack, Swedish manufacturer Effecta, and Austria’s Fröling (Effecta and Fröling also distribute to the US). These boilers all boast improved designs and smokeless operation, with running efficiencies often over 90% LHV (normal wood stoves have efficiencies ranging from 60-90%). If lambda control is turned off or is defective, the boilers operate as conventional boilers without the increased efficiency. Prices for the boilers can average about 20% more than non-lambda boilers, typically ranging from $8,000 to $14,000, but often more, depending on model, market and desired energy output. To our knowledge, no wood stove is yet using a Lambda sensor, but it is likely just a matter of time until we see these higher efficiency stoves on the market.


  1. Posted by Marc Caluwe:
    Lambda sensor controls are definetaly a big improvement.
    In cars this technology is used in combination with catalytic combsutors.
    In my opinion they should be used in biomass applainces in a similar manner: Lambda sensore in combination with catalytic afterburn and/or elctrostatic "filter".
    This way you can cover high burn, low burn and anythng in between.
    Just a lambda sensor by itself has limited cleaning possibilities.
    Marc Caluwe

  2. A new product to the market, made right here in the USA is the Woodmaster Flexfuel boiler which uses lambda technology to achieve >95% efficiency -- a gasification boiler that can burn cord wood or pellets.

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