filter setup

HEPA home furnace filter reduces PM2.5 emissions

HEPA home furnace filter reduces PM2.5 emissions

There are a number of methods to reduce personal exposure to household air pollution associated with using biomass fuel for the daily cooking and heating taking place in nearly 40% of global households. These most commonly include 1.) Increasing ventilation rates, 2.) Installing a chimney and 3.) The use of cleaner fuels and cook stoves. A recent ARC paper available (free for a limited time) at:

investigates two less-commonly considered methods: 1) Reducing exposure through filtration and capture of PM2.5 and 2) Avoiding making emissions by using made charcoal and retained heat for cooking.

filter setup

The smoke is pulled through the filter and less smoke exits the room

When cook stoves are operated inside an enclosure from which smoke is pulled through an inexpensive HEPA-type furnace filter before exiting to the outside, the personal exposure levels, room concentrations, and external pollution are reduced. To test this method, an enclosure was built from which a box fan pulled the air and PM2.5 through four different furnace filters. The rate of PM2.5 production (mg/min) exiting the filter was monitored with gravimetric measurement under a LEMS emissions hood during the high and low power phases of the Water Boiling Test 4.2.3 conducted on a biomass rocket stove with forced draft.

The average of seven baseline emissions tests with no filter was 7.5 mg/min of PM2.5. The average of seven tests using the highest quality furnace filter (3M 2200) was reduced to 1.5 mg/min and the difference was significant at 95% confidence. The use of retained heat to simmer dramatically reduced emissions of PM2.5 by burning the boil-phase-made-charcoal and using retained heat in the stove while 5 liters of covered water were simmered for 35 minutes.

Refractory Metals at 1,000 Hours in Salty Biomass Combustion Chambers: Big Problems

Energy for Sustainable Development 37 (2017) 20–32, Alloy Corrosion Considerations in Low-Cost, Clean Biomass Cookstoves for the Developing World Michael P. Brady, et al.

Michael Brady and others examined the following:

“Corrosion evaluation under cookstove-relevant conditions was studied by two methods: 1) lab furnace testing and 2) in-situ exposure in an operating cookstove. The lab furnace testing was conducted in air with 10 volume percent of H2O to simulate water vapor release from burning biomass, and direct deposition of salt onto the test samples to simulate the burning of highly corrosive biomass feedstocks. In particular, relatively high levels of salt species are encountered in many types of biomass and can lead to significantly accelerated alloy corrosion rates (Antunes and de Oliveira, 2013; Baxter et al., 1998; Saidur et al., 2011; Okoro et al., 2015). The in-situ cookstove testing was conducted using wood fuel that was pre-soaked in a salt water solution to yield accelerated, highly corrosive conditions.”

“Each day of testing, cookstoves were burned continuously for an average of ~6 h. The average fuel consumption rate was 570 g/h. To determine the range of temperatures that the alloy test samples would experience, a thermocouple was placed inside the chimney of each stove at the same height as the coupon fixture. Typical combustion chamber temperature profiles for the cookstoves, where test coupons were placed, are shown in Fig. 2. The average gas temperature range during steady state in-situ testing was 663 °C ± 85 °C”

“Much faster corrosion rates were observed in the 800 °C lab furnace testing where evaluation of most alloys stopped after 500 h of exposure due to excessive corrosion. Of the alloys tested to 1000 h, only the FeCrSi and pure Ni samples exhibited good corrosion resistance. The FeCrAlY and 310S alloy samples were consumed through-thickness in some crosssection locations.”

“Type 201 stainless steel, type 316 L stainless steel, and the 12 and 20Ni AFA alloys all exhibited relatively poor corrosion resistance in the in-situ cookstove testing, with metal losses in excess of −200 μm after only 500 h of exposure, consistent with the lab furnace trends. The types 310S and 446 stainless steels exhibited moderately worse corrosion resistance, with metal loss values of −190 μm and -230 μm after 1000 h. Despite exhibiting the best corrosion resistance in the lab furnace testing, the pure Ni suffered from −300 μm metal loss after only 500 h in the in-situ cookstove testing.”

“These findings indicate that ferritic FeCrSi alloy compositions in the range of ~ Fe-(13-17Cr)-(2–3.5)Si-(0.2–1)Mn-(0.3–0.7)Ti-(0.1–0.6)C wt.% show promise for use in biomass cookstove combustor components.”

In salty conditions should we switch to the use of refractory ceramic, I wonder?

Dean Still


Protecting Health with Biomass Cooking Stoves

justaIt was great to attend the Global Alliance Forum a week ago in Delhi, meeting and learning from so many colleagues. Dr. Omar Masera presented a paper that summarized a survey of fugitive emissions from plancha type stoves in Mexico. The World Health Organization Indoor Air Guidelines figure that 25% of the total emissions going up a chimney end up inside the house because stoves and chimneys are leaking that much into the room air.

It’s starting to rain here in Oregon and on my daily drive to work smoke is pouring out of chimneys again while the indoor air stays clean as the draft in the chimney puts the emissions outdoors. These chimneys are well built and are maintained so almost no smoke pollutes the home. The chimney is located several feet above the peak of the roof to encourage the pollution to drift away from the windows and doors. Without chimneys the high levels of smoke emitted from these heating stoves would make living indoors very uncomfortable.

The five plancha cooking stoves in the study were also not very clean burning (Tier 1 for PM 2.5 for high and low power) but results from 54 tests showed that fugitive emissions into the room were only 1% of the totals resulting in Tier 4 for Indoor Emissions of PM 2.5 and CO (Medina, et al., Development Engineering Volume 2, 2017, pages 20-28). Why have chimneys, the historical, relatively inexpensive, and most practical technology to protect health, not become a most popular intervention? At ARC we try to combine clean combustion and superior heat transfer efficiency with a chimney so that the stove brings a synergy of improvements to the consumer.


Methods to Improve WBT Repeatability

At the InStove HEARTH conference Sam Bentson gave a talk about how to make WBT laboratory test results of rocket stoves more repeatable. The presentation is available here, and the accompanying video may be viewed here. Thank you to InStove for organizing a great event.

InStove HEARTH Conference

Our friends at InStove are hosting a stove conference next weekend. We hope to see you there. Click below for the schedule, and read on to learn more.


Household Energy and Renewable Technology for Humanity Conference to take place in coming weeks
Thursday, August 17th to Sunday, August 20th in Cottage Grove, Oregon, InStove and Burn Design Lab will co-host the annual “Household Energy and Renewable Technology for Humanity” (HEARTH) conference. HEARTH brings together: implementers, funders, researchers, volunteers, and other interested stakeholders in the international, community-based development sector.
Each day of the event covers a specific theme: Thursday is dedicated to discussions between funders and nonprofits; Friday focuses on program development and collaborative partnerships; Saturday covers renewable energy and cookstoves; and Sunday concentrates on resilience and disaster preparedness. Camping on the InStove campus is free to attendees, any or all days, and the event immediately precedes the 2017 Solar Eclipse (free viewing glasses will be available to all participants and their families). Childcare is provided. Register at:
dean, kirk, dennis cat pee 2016 crop

Most Commercially Successful Stove in your Area?

ARC is involved with many cook stove projects around the world. Mostly we assist with technical information to improve emissions and performance and to set up stove laboratories. Once in a while we help commercial projects to manufacture stoves, get carbon credits, or write business plans. Each year we host at least one hands-on conference, “Stove Camp“, during which inventors and policy makers learn from each other to advance the state of the art of biomass cook stove technology. Could you help us to get a feeling for the ‘big picture’ of the commercial stove market so that we can better direct the creative energy during our next Stove Camp? We very much appreciate your help!


Stove camp attendees


We hope that you might take a moment to inform us about stoves sold in your country.  Could you provide responses to the following questions in a reply to this email? THANK YOU!!!

1.)    Where are you located?

2.)    What type of stove is purchased most often?

Charcoal Stove

Rocket Stove


Plancha stove

Institutional stove

Coal stove

Other stove

3.)    Can you estimate how many stoves are sold?

4.)    Where are the stoves purchased?

5.)    About how much does the stove cost?

6.)    If you were going to sell a stove in your region what are the two most important features it should have?

7.)  Would folks purchase a stove with a chimney?

THANKS AGAIN!        All answers are private, of course.




Dean and Sam

Clean Burning Biomass Cookstoves: A Quick Summary

Clean Burning Biomass Cookstoves: A Quick Summary

  • The stove body and interior (including the combustion chamber) is low mass and insulative. The heat from the fire goes into the cooking process and is not diverted into the stove.
  • The heat transfer efficiency is close to optimal resulting in over 40% thermal efficiency. One successful technique is to combine moderate firepower (2.5kW) with very small channel gaps (6mm) around the pot. Burning less wood results in fewer emissions.
  • Emissions are reduced by increasing combustion efficiency. An appropriate amount of wood gas is made. The rate of reactions is controlled by adjusting the primary air or by metering the fuel.
  • A zone of mixing of air, gases, smoke, and flame is created using jets of secondary air. The jets of secondary air can be powered by natural draft in a Top Lit Up Draft stove or by forced draft in both Rocket and TLUD stoves.
  • Increasing the velocity of the jets of air can improve the effectiveness of the zone of mixing.
  • The cooling effect of the secondary air jets is not allowed to decrease thermal efficiency below 40%.
  • The amount of flame, air, and wood gas entering the zone of mixing is adjusted until close to optimal combustion efficiency is obtained.
  • Emissions in the exhaust stream can be further reduced with a catalyst.
  • Removing the emissions from the living space in a chimney is mandatory in the United States. The ARC stoves have chimneys to comply with new WHO guidelines.
  • The prototype stove moves through an iterative development process by testing one change at a time under the emissions hood. The Water Boiling Test and the Controlled Cooking Test are both used to evolve a stove that is clean burning, fuel efficient, and cooks as well or better than the local model.
  • The cooking function of the stove is designed by local users. The market viability of the product is determined by field testing involving stakeholders such as distributors, manufacturers, funders, consumers, etc. Market testing precedes and informs manufacturing.
  • Reducing adverse health effects requires the new stove to be a successful intervention. The intervention involves many infield factors that influence the effectiveness of the whole package. Identifying these factors begins the process of creating the successful intervention.
  • The stove is only one part of the successful intervention! A recent study in Malawi (commentary, article) of a clean burning stove found no decrease in PM exposure related illnesses, but less than 50% of the stoves were in use.

From “Clean Burning Biomass Cookstoves” found for free at

Dr. Tom Reed: The Father of Clean Burning?

Dr. Tom Reed: The Father of Clean Burning?


Well, Tom is certainly one of a small group including Paal Wendelbo and Ron Larson who started making “Tier 4” stoves in the 1980’s. I think of Tom when I light his wonderful forced draft TLUD camp stove which I do to demonstrate a simple ‘no smoke’ stove. Tom’s webpage says,”  In 1972 Tom Reed became concerned about the energy and fuel futures of the U.S. and began working on alternate fuels on the side while working at MIT in the field of solid state research. He was the first person to use alcohol blends during this period and when he wrote “Methanol – A Clean Fuel for the 21st century”, for Science magazine, it changed his career. In this article he said that for the short term methanol would be made from natural gas, but in the long term biomass could supply our needs forever.

Looking out of the ARC office windows, the rural Oregon road that curves past the campus is lined with 100 foot tall trees and the forest, even after decades of logging, is immense. Learning how to cleanly combust wood seems important here in the US as it does in other countries. Sustainably harvested energy is only amazing if it does no harm when burned and complete combustion opens a carbon neutral alternative that may be necessary in all sorts of applications.

How close is the complete combustion of biomass? Pellet stoves, industrial burners, and forced draft in general gets pretty close. Scrubbing the remaining emissions gets closer. In the cook stove world progress has been faster than I imagined as back yard R&D coupled with university analysis, supported by the DOE and EPA, inches science closer to the zero emission goal. As I envision the steps needed to complete the understanding leading to complete combustion, I’m thinking that reaching the goal is almost inevitable, with thanks to true believers like Dr. Tom Reed who helped to start the ball rolling.

catalyst box

How to Install a Catalyst in an Existing Heating Stove

How to Install a Catalyst in an Existing Heating Stove

catalyst box

When starting a cold stove the catalyst is disengaged from the gas stream by pulling on a steel rod. A green light will indicate when the stove gases are above 600F. The catalyst can then be engaged by pushing in the rod.

In one experiment in the ARC lab the installed catalyst reduced the emissions of PM 2.5 in a simple steel box stove made in Mongolia to about 1g/hour which meets the 2020 EPA Heating Stove Standard.

The following is a summary of a January/February 1983 article from Mother Earth News that describes design principles for installing a catalytic converter in a wood burning stove:

  • Ceramic or metal catalytic converters are coated with platinum and/or palladium and/or rhodium.
  • A catalytic converter can reduce the ignition temperature of carbon monoxide and hydrocarbons from upward of 1300°F to the 500-­700°F range.
  • Once the smoke passing through the catalyst reaches that threshold, it will oxidize as long as the combustibles in it are well mixed with a sufficient supply of air.
  • After it is “lit,” the converter will produce enough heat to maintain ignition, even though the temperature of the incoming “wood gas” may drop slightly below 500°F.
  • The basic concept can be applied to just about any roughly cubic metal (steel or iron) wood burner.
  • Since the converter must reach a temperature of at least 500°F before it “lights off,” a location close to the fire will insure that the unit starts working as soon as possible and continues to do so throughout the burn.
  • It is strongly suggested that a baffle arrangement is incorporated, diverting flame, residues, and ash, since eliminating the baffle could result in drastically shortened catalyst life.
  • There must be adequate oxygen at the catalyst, however, it was determined that specific provisions for secondary air weren’t needed. Under all burn conditions, there was always an adequate air supply remaining at the converters.
  • Hotter air (both primary and secondary) means better performance. Well­ warmed primary air encourages efficient primary combustion, and hot secondary air is vital to maintaining ignition temperature at the catalyst.
  • A well­ sealed, strong bypass valve is mandatory. Even though the cell structure of the catalyst is relatively open (in comparison with that of the automotive variety), the unit does restrict natural draft to some extent, particularly when the catalyst isn’t lit. For that reason, there must be a valve that allows you to shunt smoke around the catalyst while a new fire gets going and whenever the stove’s doors are opened.
  • As we’ve already mentioned, the single most important precaution is to always bypass the converters when the doors are opened. Furthermore, that same valve will have to be open while you’re getting a fire going.
  • And should the catalyst go out for some reason, we’ve found the thermometer to be the only easy way to tell.
  • After the charge of wood burns down — but not out — you can open the bypass, add more fuel, and then close the bypass immediately.
  • Materials such as coal, wood pellets, paper with colored ink, tires, plastics, and treated or painted lumber, may “poison” the catalyst and render it ineffective.