Around half the people in the world and as many as 90 percent of rural households in developing countries cook using solid fuels or biomass, everything from coal to wood, dung and agricultural wastes. When such fuels are burned in rudimentary stoves, as is often the case, poor combustion results in high levels of indoor air pollution (IAP). Particularly damaging are particulates, which get into the lungs and may cause respiratory disease, and carbon monoxide. In poorly ventilated dwellings, IAP can be 100 times higher than acceptable levels, which the World Health Organization has designated as 50 μg/m3 small particles and 10 ppm carbon monoxide, both measured over a 24-hour period.

Pollution from cooking fires has been implicated in the deaths of nearly 2 million people a year, mostly due to diseases such as pneumonia, chronic obstructive pulmonary disease and lung cancer, and the toll is especially heavy on women and children. Although a number of technologies that improve cooking performance exist, they often present a dilemma for agencies hoping to use cookstoves as a means to improve health and welfare. Efficient stoves, it turns out, are often dirty, clean stoves are often inefficient and the small number of technologies that perform well across both measures tend to be expensive, require advanced manufacturing techniques and are often non-intuitive to use. The potential availability, affordability and accessibility of any such technology remain necessarily limited.

One technology that can be used to effectively reduce levels of IAP is the smoke hood, which is often constructed from sheet metal and draws smoke upwards and through the roof, drastically reducing the levels of indoor smoke. Smoke hoods can be placed over open fires or improved cooking stoves and can be adapted to suit the country and local community requirements.

Pollution from cooking fires has been implicated in the deaths of nearly two million people a year. The toll is especially heavy on women and children.

Following pilot projects conducted in Kenya, Tanzania and Nepal in 2009, the international development and technology charity Practical Action embarked on the Healthy Hoods project in collaboration with the global Bosch and Siemens Home Appliances Group (BSH) and the Bundeswehr University Munich. This project included the development of an online tool enabling users to input a variety of factors to produce a diagram and dimensions of an optimal smoke hood for their particular situation.

The project aimed to design and optimize smoke hoods for developing countries and establishing construction guidelines, specifically to:

  • Increase awareness of the adverse health impact of IAP and create a demand for the smoke hoods.

  • Demonstrate a sustainable mechanism of market promotion for this technology.

  • Disseminate project learning and knowledge to a wider audience.

This case study examines the experience of implementing the Healthy Hoods program in the Gorkha region of central Nepal. The lessons Practical Action and its partners learned from this experience will enable the program to more widely disseminate smoke hoods in other locations.

Fire and Smoke

The Gorkha region is an area that needs the means to improve its indoor air quality. The region is in the highlands of central Nepal at an elevation of 1,135 meters above sea level, and it has a population of around 300,000 residents. Due to cold temperatures in the region, indoor fires are used not only for cooking but also the heating of indoor spaces. The use of solid fuels and traditionally inefficient cooking stoves in poorly ventilated houses has resulted in IAP that far exceeds maximum levels as recommended by the WHO. This in turn has resulted in increased respiratory problems for residents, especially for women and small children.

In 2011, Practical Action UK and Practical Action Nepal collaborated with Sam Shiroff, BSH’s Senior Sustainability Specialist, and Dr. Liz Bates, an international household energy specialist, and researchers at Bundeswehr University for the Healthy Hoods project. This public-private partnership combined Bundeswehr University’s thermodynamic expertise, BSH’s marketing experience and corporate social responsibility goals, and Practical Action’s technical expertise, for a holistic approach to the problem of IAP.

Smoke hood design

The main objective of Healthy Hoods was to design a smoke hood that would remove significant amounts of IAP, while offering a model that would not interfere with families’ traditional practices and allow for them to place efficient—though not necessarily clean—cookstoves beneath it. The idea was that by using some of the most advanced computerized fluid design techniques it might be possible to dramatically improve the performance of the hood while keeping manufacturing costs low. Moreover, the smoke hood was designed to be simple enough to be manufactured locally and offer adaptations to accommodate local needs and habits.

Prior to this project, Practical Action had already completed field research with an initial smoke hood design. Practical Action learned that such hoods must remove adequate amounts of smoke while allowing for space-heating and for the smoke to be used for curing crops, smoking meat and coating wooden rafters with a layer of carbon to preserve the wood. The initial project achieved some notable benefits, with approximately a 60 percent reduction in smoke and a reasonable acceptance of the technology—by the end of this field test, about 1,600 families from three districts were using the smoke hoods.

The Healthy Hoods project was carried out over a two-year period, beginning in January 2011. It was divided into two phases. The first six months were allocated for testing the technology and carrying out an acceptance study and design modifications, while the remaining time was allocated to scaling-up the optimized smoke hoods. The second scaling-up phase of the project was based on social marketing, fabrication and installation, access to credit and quality assurance.

Testing the Technology

The Department of Thermodynamics at Bundeswehr University designed the optimized Healthy Hoods. Researchers there used fluid dynamics software to model the flow of hot gases through the hoods. Gases in a pipe tend to flow smoothly until they reach points where either the direction or the cross-section of the pipe change. At such points, vortices and eddies can form, and the simulation model mimicked the issues that had been observed in the Nepali households during field tests.

For instance, the model found that if the front opening of the smoke hood is too large relative to the cross-sectional area of the flue, then gases can escape under the lip of the hood. The model also showed that vortices can form along the bottom corners of the hood, allowing smoke to escape at such places. Smoke hoods that had already been installed had exhibited this, with smoke marking the top edges and bottom corners of the smoke hood, and households complaining of smoke “blowback” on windy days.

Small changes in various key measurements were made to address these issues. Using mathematical modeling, the researchers in Munich optimized the ratio of the size of the opening to that of flue and created a lip along the vertical edges of the front opening to eliminate the vortex and to add stability to the hood. Fitting a cowl to the top of the flue reduced many of the issues associated with blowback on windy days. (Although an H-shaped cowl is more efficient many households preferred a smaller cowl which is not as efficient but removes sufficient smoke.) Finally, leakage between the smoke hood flue and the roof was resolved using a “skirt” of steel from the roof down to the joint.

Over the course of the design optimization, smoke reduction increased around 65 percent. However, science aside, it was critical to engage the local community in the design of the hood. Only the end users can know which issues are most important to the community, and which smoke hood design would best meet their needs and achieve the greatest acceptance.

Science aside, only end users know which issues are most important to the community, and which hood design would best meet their needs and achieve the greatest acceptance

Researchers developed and proposed different designs of smoke hoods, each varying across parameters such as size, shape of stake (either rectangular or round), and shape of cowl (single cap, double cap or H-shape). Mixing and matching these variables resulted in 32 different improved smoke hoods that were fabricated locally and installed in eight village development committees (or VDCs). This was a relatively small study due to high transport costs.

The project identified 50 potential local manufacturers and provided them a seven-day intensive training in the production of smoke hoods. That was followed by on-the-job mentorship to include skills in entrepreneurship and business management.

The trained manufacturers work in teams of three to five people. Since the fabrication of a smoke hood is relatively easy, the workplace can be set up wherever it is required, and most have been set up close to the user communities. The local cooperatives support the manufacturers by providing temporary space for the workshops.

It takes one full day for a skilled three-person team to manufacture and install a smoke hood. The team receives around NPR 1,500 (US$17) per hood, which provides an income of NPR 500 per person per day, a good income in rural Nepal. To diversify their businesses, the manufacturers also produce a variety of household items, including grain storage bins and trunks.

A local quality control group, including representatives of the local cooperative, users and the local government, was formed in each village to check on the end product. Warrantee cards were issued by the manufacturers with a free one-year maintenance service guarantee. Quality indicators of the product were developed and efforts were made to standardize smoke hood design based on local needs. Periodic monitoring of product quality and after sales services were conducted by trained staff.

After installation of the smoke hoods for testing purposes, an acceptance study was carried out through a team of consultants. Based on the recommendations generated from that study, further modifications were made to the design.

Creating Demand

Following the initial technology testing and acceptance study, the Healthy Hoods project used a demand-based approach to create a market for the optimized smoke hoods technology. Due to a low awareness of the problem of IAP in the local communities, that approach required extensive time and effort.

The project launched awareness campaigns to train approximately 25,000 people on the danger posed by IAP and used FM radio broadcasts and monthly meetings of cooperative members to disseminate IAP-related information. It taught techniques for drying wood fuel, reducing personal exposure to smoke and the time spent for cooking, using pot lids for cooking efficiency and adopting better hygiene. The project disseminated educational materials on health and the economic impacts of indoor smoke to 5,017 households and trained 96 Female Community Health Volunteers, 50 teachers, and 1,350 students on the adverse health impacts of IAP. All of this was done with the close cooperation of local health service centers.

Monthly meetings were the most effective approach in creating demand for smoke hoods. Another successful approach was identifying community leaders as early adopters and convincing them to install smoke hoods at their respective homes. This provided an opportunity for the community to observe the benefits of the new technology and that in turn triggered an increased demand in the project areas.

Creating awareness of the problem wasn’t the only means to build demand. A Healthy Hood costs about NPR 6,000—a large sum for a poor family to pay upfront. One of the major goals of Healthy Hoods was to establish sustainable financing so that the project was not dependent on subsidies. A revolving fund mechanism was organized by nine local cooperatives in order to provide loans to households for smoke hood installation. A deposit of NPR 1,000 per household was required to order a smoke hood, with the remaining NPR 5,000 granted as loan from the cooperative. The terms and conditions of the loan are very similar to a standard loan system, with the exception of the interest rate, which is 5 percent or less, compared to a standard rate of 18 percent.

About 5,000 households have been granted loans totaling NPR 4,003,200, and repayment rates are regular and as per the guidelines provided by the project. At the end of January 2013, approximately NPR 588,800—14.71 percent of total disbursed loan—of loans repayments had been collected and the cooperatives were successfully using the revolving fund for the scaling-up of smoke hoods and other income generating activities.

Number of smoke hood installations per month

A total demand of 834 smoke hoods was received during the two-year project period, not including the 32 hoods installed for testing purposes. At the start of the project, installation of smoke hoods was slow, though this increased dramatically at the midway stage, but decreased towards the end of the project. However, the local cooperatives continue to receive further loan requests for the installation of additional smoke hoods, with the number expected to increase in the future.

Indoor Air Pollution Monitoring

To gauge the success of the smoke hoods, the project needed to measure the improvement in indoor air pollution after installation. The project monitored the levels of particulates and carbon monoxide over a 24-hour period using equipment placed inside the kitchen, 1.3 m away from and 1.3 m above the stove, ideally attached to the kitchen wall. For particulate matter, the main tool adopted was a gravimetric measure, where PM 2.5 particles were collected on a filter and weighed. GasBadgePro single gas monitors were used to measure levels of carbon monoxide.

Continuous measurements were taken to account for variations in total emissions throughout the day. The results showed that levels of IAP were found to be significantly reduced after intervention with the installation of smoke hoods reducing levels of both particulates and carbon monoxide. Specifically:

  • PM2.5 (24 hours average) 753 μg/m3 with traditional stove and 118 μg/m3 after smoke hood intervention.

  • Carbon monoxide (24 hours average) 32.13 ppm with traditional stove and 2.25 ppm after smoke hood intervention.


Following the installation of smoke hoods, user households experienced a drastic reduction in smoke levels inside the kitchen. The IAP survey results show that there was a reduction of IAP by about 82 percent after intervention. Installation of smoke hoods in 834 households contributed to improved respiratory health of approximately 1,670 women and children in the project areas. Within a few months, users noticed improvements in their health and in particular a reduction of respiratory problems in children, with less frequent headaches and eye problems. Cleanliness is another benefit of the smoke hoods noted by users.

An outcome of the project’s education campaign is that more than 55,000 members of the rural population are now aware of the dangers of IAP and how to combat it. In addition, it was noted that due to increased awareness, a few households have also started to look for other low-cost options for cooking, such as mud improved stoves.

There have been some positive add-on outcomes that don’t directly relate to the improvement in indoor air quality. The rural population in the project community is now better educated on the provision of revolving funds and microfinancing. Instead of subsidies, soft loans were provided to customers to buy and install smoke hoods through local cooperatives. The project provided seed money as a grant to local cooperatives to run the revolving funds and provide capacity-building training to local cooperatives so that they could manage the funds. Reports indicate that the local cooperatives in the different villages are running the revolving fund satisfactorily, while fund mobilization is good and repayment rates are acceptable.

More than 55,000 members of the rural population became aware of the dangers of indoor air pollution as a result of the education campaign; a few households have started looking for low-cost options for cooking.

The nine local cooperatives involved in the scaling-up of indoor smoke-alleviating technologies are now able to work with a range of technologies which contribute to improving indoor air quality. Additional benefits include an increase in cooperative membership and an increase in knowledge of management skills, which has improved overall performance, including developing connections with various district stakeholders.

Of the 50 local artisans initially trained to fabricate and install smoke hoods, 23 have adopted smoke hoods supply businesses, with the hope that these manufacturers will establish or expand on smoke hood manufacturing workshops. And a market-based institutional delivery system was established to ensure quality and a continuous supply of smoke hoods. Local quality control mechanisms have been established to ensure high quality is maintained via warrantee cards.

Scaling-Up, Replication, and Future Directions

Key components of the scaling-up phase

Since the smoke hoods have a long lifespan, the need for manufacturers to install them will gradually diminish over time, as many of those trained to do installations are restricted by the physical distance between themselves and new markets. A solution from Practical Action is to manufacture the smoke hoods in a central workshop and train local builders to assemble “flat-pack” versions of the hoods. This would allow less skilled people to install the hoods wherever they might be needed, but not leave the original manufacturers unemployed once all the villagers had them in their homes, as the manufacturers would have smoke-hood construction as part of a set of skills rather than just one specific skill.

One issue with scaling up the project is that since smoke hoods are not stoves, it has proven difficult to raise their profile within the international arena and convey the fact that a smoke hood plus an improved stove can be a very effective combination, or that a smoke hood on its own can contribute to improved indoor air quality. The name has recently been changed to “hoodstoves” in an attempt to define the technology in a single word, but the challenge of raising their profile is ongoing.

This case study was written by Min Bikram Malla, Elizabeth Bates, Sarah Matthews and Mattia Vianello.

Min Bikram is a project manager working on indoor smoke alleviation projects funded by UKDFID, USEPA/PCIA, GACC and Bosch Siemens in Practical Action Nepal Office. He holds a Master's degree in Economics from Tribhuvuvan University of Nepal.

Elizabeth Bates is a household energy specialist. A mechanical engineer, she worked for Practical Action as a project manager before becoming an independent consultant.

Sarah Matthews is a water, sanitation and hygiene expert at Practical Action with experience in community based research/participation in remote areas.

Mattia Vianello is an energy consultant at Practical Action focusing on the role of energy access as enabler for development. He holds a MSc in Science and Technology Policy and Management from the University of Edinburgh.