Wednesday, June 14, 2017

Thermoelectric Wood Stove, Solar Power, and a Floating Cabin!

Guest blog post, by Margy Lutz

Finally this winter, our thermoelectric wood stove generator is fully operational. Following our test runs, we placed the pump to recycle cold water down in the lake water under the cabin. In winter, it gets about 5 degrees C (41 F). That's plenty cold for a good differential between the 300 degrees C on the hot side.

Most system owners don't live in a float cabin four feet with a constant cold water source under the floor. The typical user has to use a recycled liquid (usually including a water/antifreeze mixture) that runs through a radiator for cooling.

In addition, a charge regulator/controller is used to protect the batteries and prevent overcharging. The model that came with our system has lights to let you know the status of the charging process.

Wayne likes to know more about the charge we are getting. He installed an ammeter and a volt meter. The switch in the middle controls the water pump down below the cabin. To maximize the charge to our cabin battery bank, we've installed a separate solar panel and two six volt batteries wired in a series to run the pump.
Living off the grid has its challenges, but having an alternative power sources has made our winters much brighter (pun intended). Do you generate power? What are some of the solutions that have worked for you? -- Margy

Postscript by Ken Adler, AGH Technical Advisor: 

Congratulations to Wayne and Margy on their thermoelectric wood stove. In a follow-up communication with Wayne, he reported that they are no longer using the system because the thermoelectric modules failed. Wayne doesn’t know why they failed, however, the most common reason for failure is overheating.  The modules can also fail if Bellville washers are not used to allow the module to expand and contract during heating and cooling. Wayne also reports,

Even when I was partially (marginally) operational, I produced less than 2 amps at 12V DC (23 watts) to recharge my cabin battery bank. This would have been enough to put a top-off charge on my cabin batteries (normally recharged via my solar system), particularly valuable in the winter when solar power is minimal and my wood stove is operating nearly 24-7. The primary reason for the low amperage was the need for a 1,8 amp 12V (21.6 watts) water pump to feed the cold side of the modules. In many ways, I reside in the perfect test location for this thermoelectric system, since 

I have a nearly infinite supply of very cold water 4 feet below my wood stove. I live in a floating cabin on Powell Lake BC, and the lake is extremely deep and very cold in all seasons. What an opportunity to serve as a source of cold water through the cooling system! The pump only needed to pump the cold water up 4 feet and then outflow back into the lake. Even with this tremendous advantage, I couldn’t get everything fully operational.

Does this make me a non-believer in thermoelectric from a wood stove? Absolutely not — I still believe this is an important future source of electrical power in my cabin, since even a top-off voltage during the solar-depraved Canadian winter would be worth the price. I’d be one of the first in line if a recreational property thermoelectric system was available, and I’d be quick to try again. Thus, I wish you all of the best with your preparation for the 2018 conference. I’ll be following the results closely.

In an earlier post, Wayne reports that he is using three 25 watt thermoelectric generators for a total rated power of 75 watts of output, however, he’s only getting 23 watts of power for his battery. Part of this is due to his pump, which is drawing almost 22 watts of power. If you are interested in building your own thermoelectric wood stove, there are a few improvements that you may want to consider. First, TEG suppliers (see our resources page) now sell more efficient lower wattage pumps. Second, consider starting with a thermoelectric generator rated for 100 to 200-watts. While this is more expensive, if you go with a smaller system much of your power will be consumed by the pumps and/or fans you need to cool the modules. Third, Bellville washers are critical for allowing the modules to expand and contract.

If you are interested in designing a thermoelectric wood stove for our 2018 Wood Stove Design Challenge, please visit our web site for more information. For more information on Wayne and Margy’s life on a floating cabin, please visit their blog at Powell River Books Blog.

For an overview of the potential of thermoelectric wood stoves, click here.

Monday, June 5, 2017

Hybrid Residential Solar and Thermoelectric Power Generation

by Ken Adler, Senior Technical Advisor at the Alliance for Green Heat

Some of you may be wondering about thermoelectric wood stoves and why we decided to include them in the 2018 Wood Stove DesignChallenge, which will be held in November 2018 on the Washington Mall.  Our goal of this competition is to support development and commercialization of a revolutionary thermoelectric wood stove that produces electricity equal to 50 percent or more of the winter time output of a residential solar photovoltaic system. By combining a thermoelectric wood stove and a residential solar PV system and home battery, like the TESLA Powerwall, we can support residential and grid-based distributive power goals, and incentivize greater investment in solar power. 

Specifically, thermoelectric wood stoves can help solve the problem of low winter time solar PV output in northern climates, where useful solar radiation is limited to 2 - 4 hours per day.

While a thermoelectric wood stove may sound revolutionary, the technology behind the stove has been used since the 1980s in oil and gas field operations, where methane gas provides a low-cost source of heat to power the thermoelectric generator. Wood stoves, like waste methane gas, can provide a free source of heat for the thermoelectric generator.
Alphabet Energy Thermoelectric Generator

Thermoelectric generators are like solar panels, however, instead of turning light into electricity they turn heat into electricity. To generate electricity, one side of a thermoelectric module is heated by the wood stove while the other side is cooled with either an air or water-cooled heat sink. For applications above 100-watts, water-cooled heat sinks are the most common approach because of their ability to extract greater amounts of heat from the thermoelectric module.

60-Watt Water Cooled Thermoelectric Generator

In northern climates like New England, Canada and northern Europe, low winter time solar radiation increases the cost and reduces the efficiency of solar PV systems, and the cost-effectiveness of battery storage systems like the Tesla Powerwall.  According to NREL, solar radiation in northern areas like Vermont peaks at 6.0kWh/m2 in June and declines to 1.7kWh/m2 in December. This means that an average 4,000-watt residential solar system will go from producing 571kWh in June to 191kWh in December--a 66% reduction is solar power output.  This project will demonstrate how a thermoelectric wood stove can cost-effectively supplement a solar PV system.

Building on our experience from 3 previous Design Challenges, we will work with wood stove manufacturers, universities and others to build and test 100 to 200-watt thermoelectric wood stoves that could effectively increase by 50% the winter time output of a 4,000-watt residential solar PV system.   

Thermoelectric generators are currently sold as accessories for wood stoves; however, these accessories are limited in size and efficiency. By integrating a thermoelectric generator into a wood stove we can achieve far greater power output, efficiency, and lower cost. For example, a wood stove with a 150 to 200-watt thermoelectric generator operating 20 hours per day could generate 93 to 124kWh of electricity per month, which compares favorably with the December solar PV output of 191kWh in Vermont.
Russian Thermoelectric Wood Stove 
(not certified for sale in the U.S.)

There are several reasons why now is the time to consider thermoelectric wood stoves. First, the price of the thermoelectric modules, which are a component of the TEG, has dropped substantially because they are now being mass produced in China.[1]  Second, the EPA’s recent wood stove NSPS regulation is helping to make new wood stoves cleaner and more efficient and, coupled with cordwood testing and automated features, a new generation of cleaner stoves could also generate electricity. Third, thermoelectric wood stoves can produce electricity up to 24 hours per day eliminating load management concerns common with solar and wind power. Lastly, the stoves are powered by local wood supplies, making their fuel low carbon and locally sourced.

The 2018 competition on the Mall will demonstrate the role thermoelectric wood stoves can play in promoting solar power, energy storage systems and biomass energy, while also reducing energy costs, supporting climate change goals, and increasing distributive power.   

[1] The cost of a thermoelectric module has fallen below $2 per watt (uninstalled), compared with $3.50 per watt for solar panels (installed).

Sunday, June 4, 2017

Coal Heating in the United States

By John Ackerly & Melissa Bollman
Alliance for Green Heat

This paper was prepared for the Warsaw Stove Summit which brought AGH and scores of experts in coal and wood heating from 19 countries to Poland in May 2017.

The US Census Bureau estimates that approximately 127,000 households used coal as a primary heating fuel in 2015, or about 0.1% of American homes. Residential coal heating dropped rapidly until 2000 and since then has been relatively stable.

More than half of homes using coal heat are concentrated in Pennsylvania and New York, right where it is mined. It appears to be based on cultural traditions and local support for local jobs because its still a very inexpensive way to heat and easy to transport. Most of the United States has no restrictions on coal heating and there have been few attempts to restrict it. Rather, it seems to have gradually died out except in pockets of states where anthracite is mined. Bituminous and sub-bituminous coal is much more widely dispersed but it is used far less than anthracite.

Coal stoves, particularly those fueled with anthracite coal that principally comes form Pennsylvania, typically have less particular matter than wood or possibly even pellet stoves. However, their health impacts may be far worse, as coal often emits high levels of SO2 and oxides from nitrogen.  In addition, coal often has poisonous toxins such as flourine, arsenic, selenium, mercury and lead.  For more on health impacts of coal and wood heating in the US and Europe, we excerpted key parts of a World Health Organization report here.

Who heats with coal and why?

Homes that heat with coal tend to be concentrated near anthracite coal mines and in homes with lower or mid level incomes. In the wealthier and more urban counties of Pennsylvania that are within 100 miles of anthracite mines, virtually no households heat with coal. High use of coal heat does not correlate with high use of wood heat. Both coal and wood are favored by rural, lower-income populations but coal appears to be favored near anthracite mines, and wood is favored in nearby, rural counties, according to data from the US census. The highest percentage of homes heating with coal at the county level is about 13%.

A prominent 2008 New York Times article reported that residential coal heating was on the rise, but rise was modest, and petered out a few years later. That rise corresponded with a major recession from 2007 – 2009 during which rates of wood heat soared far higher than coal. The New York Times also reported that an additional 80,000 homes use coal as a secondary heat source and the US Census reported 104,000 used it as a secondary heat source in 2005. Only 4,000 homes use it to cook with and 22,000 used it to heat domestic hot water in 2005, according to the US Census.

In 2015, the top five states for residential coal heating were Pennsylvania, New York, West Virginia, Kentucky, and Indiana. Over 50% of US homes that heat primarily with coal are located in Pennsylvania, where anthracite coal is mined.

The primary benefits of heating with coal, compared to wood, is 1. it burns for longer periods of time, so less reloading is needed and a home can easily stay warm overnight; 2. Like pellets, it can be delivered in bags on pallets by a forklift, and does not need the time consuming splitting, stacking and seasoning that cordwood needs; 3. It is even more inexpensive per BTU (assuming you don’t cut the wood yourself); and 4. It is a very dense fuel, and takes up half the space that the same amount of wood takes, per BTU.

The downside of heating with coal is 1. The odor, which most people find moderately unpleasant; 2. The black dust which is harder to clean than dirt and wood pieces from cordwood; and 3. Its hard to light, requiring most people to start the fire with wood, before switching to coal.

While the above pros and cons are widely agreed upon, other less tangible factors play a role. Coal has increasingly gained a stigma as a dirty, non-renewable fuel, whereas wood is regarded as far more environmentally friendly (even though particulate matter from wood can be equally high). On the other hand, the dwindling economic prospects of coal towns and counties tends to make those populations want to support the fuel to combat what they often see as an unfair bias against coal.

Coal and coal stoves

Coal stoves are either stokers or batch. Stokers automatically feed coal pellets (much like pellet stoves) into the stove, require electricity and only use anthracite. Batch stoves are loaded by hand and can take anthracite or bituminous.

Most coal used for heating in the US is anthracite but anecdotal estimates by experts say that no more than 25% is bituminous, primarily in areas where its abundant.

The EIA stopped collecting data on residential coal consumption in 2008. In 2007, the EIA reported that US residents consumed 353,000 short tons (320,171 metric tons) of coal, which represented only 0.03% of the nation’s annual coal use (1.1 billion short tons or around 1 billion metric tons). The overwhelming majority of course (93%) of US coal is used to generate electricity.

Usually coal is sold in 40 or 50 pound bags or by the ton. Coal may be sold directly to consumers from the mine, a fuel supplier, or a hardware store. Blaschak is one of the largest suppliers of bagged anthracite coal and sold 374,000 tons in 2014. Forty pound bags of anthracite coal (any size) from Pennsylvania usually run $6-$8. A ton of anthracite typically costs between $190 and $210 per ton, before delivery charges (which can increase price to $250-$300). One fuel seller, Central Maine Coal, sells about 200 short tons (181 metric tons) of residential coal per heating season.

Bituminous coal is usually considered a better coal for blacksmithing than heating, but can be burned in some coal stoves and is often only $80-$100 per ton.

Institutional heating with coal is somewhat relevant to residential coal heating and data indicates that institutional coal heating is declining much more rapidly that residential heating.

According to the EIA, US educational institutions consumed 700,000 short tons (634,900 metric tons) of coal in 2015, down from 2 million short tons (1.8 metric tons) in 2008. Twenty of the 57 US educational institutions that used coal in 2008 reported not using it 2015 due to sustainability initiatives. It is likely that most of the coal consumed at educational institutions is used to generate heat. Most US schools no longer heat with coal. Recent (2015-2016) news articles report that only five public schools heat with coal in West Virginia and four schools heat with coal in Cumberland, Maryland. One of the Maryland schools uses 517 tons of coal annually at a cost of $120 per ton.

Coal stove companies

Most coal stoves are made in Pennsylvania except for one big producer, Hitzer stoves located in eastern Indiana. Sales of coal stoves are reported to average 4,000 to 7,000 a year, but in 2008 they may have topped 10,000. In comparison, about 140,000 wood stoves are sold each year. There are about a dozen companies making coal stoves and one notable trend is that the larger wood stove companies are getting out of the coal stove business. Vermont Castings, Harman and Moreso used to sell coal stoves and now don’t. The one company that still focuses on both fuels is US Stove Company, based in Tennessee. Coal stoves cost about the same as wood stoves and range between $2,000 - $3,500.

Stove policy

Coal stoves remain exempt from EPA emission regulations. Coal stoves have never had a certification program at the EPA or at any state level, although the federal government and some states have indicated an interest in developing emission regulations. Regulation would likely drive up the cost of coal stoves and may reduce sales of coal stoves but other strategies may reduce their use faster and more economically. But without emission regulations, there is little data on coal stove emissions from various types of coal stoves, and there is little incentive for stove companies to try to produce cleaner stoves. Tests conducted in the 1980s suggested that wood stoves emitted higher levels of particulate matter than anthracite stoves, but lower levels than bituminous stoves (Houck, 2009). Of course, wood emits fewer other toxic chemicals than coal.

One significant policy change in 2015 was the ban on advertising dual coal/wood use in stoves unless the stove was certified with wood, and the company also tested for coal emissions and provided that data to the EPA. To our knowledge, no company has done this so no stove should advertise the ability to burn wood and coal any more.

The EPA is currently funding research on coal emissions and has developed an unofficial, draft test method at Robert Ferguson’s lab. However, this is being undertaken only because of an EPA program to change out coal stoves on the Navajo Indian reservation, not because it has any apparent mandate or serious plan to start regulating coal stoves.

It is unlikely under the Trump administration that any certification program would be initiated by the EPA, and the only state with enough coal stoves to justify the effort would be Pennsylvania, which is unlikely to do so.

Restrictions of the use of coal stoves

Unlike the United Kingdom, there has never been any national effort in the US to reduce reliance on coal stoves. Krakow, a major Polish city is banning coal stoves in 2019, after a multi-year effort to provide subsidies for alternative heating sources.

Two states – Washington and Oregon – effectively ban them because they only allow stoves that meet specific emission requirements, but those states would have very little coal heating anyway.

Many air districts that have poor air quality and high particulate matter levels employ temporary burn bans apply to coal stoves and well as wood stoves. A few jurisdictions, such as Fairbanks, Alaska, offer homeowners financial incentives to recycle their solid fuel burning appliance (including coal stoves) or replace it with a less polluting appliance (coal stoves are not eligible). However, most change out programs only remove old wood stoves and do not allow coal stoves to be replaced with wood stoves. A Pennsylvania county offered $200 to trade in old wood or coal stoves, but that program has been suspended.

Oregon is the only state where it is illegal to sell a coal stove, or any other uncertified solid fuel burning appliance. Oregon also requires uncertified solid fuel burning appliances, including coal stoves, to be removed and destroyed when a home is sold. According to the latest (2015) Census data, only 143 homes rely on coal for primary heat in Oregon.

At the local level, there may be a number of cities or counties that do not allow coal stoves, but the only one we could find is Summit County, Colorado that forbids the installation of a coal stove (uncertified solid fuel burning device) in a new home or as a replacement unit for an existing non-certified stove.

Key sources

Dr. James Houck, “Let’s Not Forget Coal,” Hearth & Home Magazine, December 2009, pp.

World Health Organization, “Residential heating with wood and coal: Health impacts and policy options in Europe and North America,” 2015.

Tom Zeller, “Burning Coal at Home Is Making a Comeback,” New York Times, Dec. 26, 2008 

Friday, May 12, 2017

A Response to James Houck’s Indictment of the NSPS

A stove being tested at
Omni lab, where Jim
Houck used to work.
In the May issue of Hearth & Home magazine, James Houck wrote a lengthy criticism of the 1988 and 2015 NSPS,  Straight Talk”, in which he took the “gloves off ... to tell it like it is.” It is essential reading for anyone who wants to better understand the science and politics of regulating wood stoves.

But let’s take this a bit further and examine some of things that Jim Houck did not mention that also have implications for the future of wood heating in America. Houck states his premise is right up front:

“The 1988 NSPS was bad.  The 2015 NSPS is bad.  They are bad technically and they are bad for the hearth industry.  Certainly they have and will provide some environmental and health benefits, but they are poorly written, they have loopholes, they have cost the hearth industry dearly [and] they have allowed gamesmanship. [...] The blame cannot be put on regulators alone: those in the hearth industry also share some of it.”

Jim goes on to explain why we are going down the wrong path.  The 2015 NSPS essentially adopts the same test method as the 1988 one: a method based on grams per unit of time, not grams per unit of fuel, or better yet, grams per unit of heat.  He also very clearly shows how both the EPA and industry have ignored basic science by, for example, claiming that certified stoves reduce pollution far more than the data shows.  The best data shows an average decline in PM of nearly 50%, yet the EPA often claims its 75% and industry 90%.

The key question is, can manufacturers make genuinely cleaner stoves regardless of the EPA regulations?  Put another way, do manufacturers have the expertise and innovation necessary to take stoves to the next level despite poor regulations, or does the NSPS retard innovation and require that stoves continue to be designed according to faulty parameters?  There are good arguments on both sides of this debate. 
The lead author of the 2015 NSPS
was Gil Wood, at right, who retired
the day the final rule was published.
Two of the greatest threats to stoves burning clean in homes are things that Houck never mentioned: tuning primary air for cribwood, not cordwood, and the EPA requirement that stoves burn at a low burn rate.  Together, those requirements almost guarantee that cordwood stoves in homes are likely to produce smoke at their lowest burn rate.

Jim Houck does not mention the upcoming switch to cordwood testing laid out in the newest NSPS.  Nor does he mention that the cordwood test method will include a cold start.  Granted, emissions will still be measured in grams per hour and the process of getting to cordwood testing is fraught with scientific, political and legal potholes.  But industry, the EPA and other key stakeholders at least see the need and value of getting there.

Houck’s article is about non-catalytic stoves.  The testing, repeatability and other issues can be very different with catalytic and pellet stoves.  Together, pellet and catalytic stoves make up one third or more of stove sales.  It should not be anathema to recognize that other technologies can achieve greater repeatability in the lab and greater consistency between the lab and the living room.  Otherwise, it makes it sound that all biomass heaters are far dirtier in the homes than in labs which is not true with pellet stoves and boilers. If consistency is the goal, we need to focus on technologies which can do that best, including automated stoves that use sensors to regulate primary and secondary air.  Homeowners can never keep track of changing combustion conditions like an oxygen sensor can.
Automated stoves that help
ensure the stove gets enough air
during key parts of the burn
cycle can greatly reduce PM in
in real world use.
It’s also worthwhile looking at regulatory frameworks in other countries to see if better stoves emerge where they test using grams per unit of heat and avoid other pitfalls of our NSPS.  Looking at non-cat wood stoves produced by various European countries, New Zealand and elsewhere, I think we can pretty safely say that our non-cat stoves measure up very well, if not better than stoves from those countries.  Part of the answer is because regulations in those countries allow for a different set of loopholes and types of gamesmanship. 

The bottom line is that it appears that despite all the failings of the NSPS, it still may be one of the best regulatory systems anywhere for conventional wood stoves.  Europeans have advanced wood and pellet boiler technology faster than the US because higher heating fuel prices and policies promoting renewable energy have led to a greater demand for efficient technology. 

Houck says that the 1988 NSPS was bad and notes that hundreds of companies went out of business because of it.  But it did result in a new generation of cleaner stoves that appear to be about 50% cleaner.  Houck recalled that we are now saddled with the legacy of the 1988 test method thanks to one stubborn regulator who strongly advocated it and subsequent bureaucratic inertia.  Making radical changes to the NSPS is difficult for the EPA, due in part to its lack of resources—a condition which is likely to get worse under the current administration.  In fact, the lack of resources at the EPA could hobble the stove industry even more than the new regulations.  As it is now, there is only one official who does enforcement, which includes approving lab certifications.  If that person’s time were to be cut back even more, it could pose serious economic consequences for manufacturers trying to get stoves to market for the heating season.

In 1988, the EPA almost adopted a test method using the Condar, a very small portable dilution tunnel that uses larger filters.  Some data from the Masonry Heater Association shows that by simply using a larger filter to catch PM, the repeatability of testing can be significantly improved (powerpoint).  But any radical change to test methods would likely have to come from a transparent process driven by an institution that has the funding and credibility to carry it out.  
Extensive round robin testing in Europe
 coordinated by BeReal should expand our
understanding of repeatability.

Universities or labs could develop of a better test method, but stoves do not have the same level of R&D support from Congress, DOE or other potential major funders that other renewables have. In Europe, there is more public funding and the BeReal project is doing far more extensive round robin testing than what Houck describes in the US.  Some agencies and groups prefer to see stove technology stagnate and have its market share wither, due to antipathy or ambivalence toward this complicated creature that can be affordable to homeowners but too often noxious to neighbors.

We will never know what would have happened if the regulators had written better test methods.  Perhaps todays’ stoves would reduce PM by 60 or 70%, instead of the 50% that Houck cites.  We also don’t know how much better stoves will be 10 years from now after the 2015 NSPS plays out.  It appears that few stove manufacturers will go out of business this time around, partially because many of them also rely on profits from their gas stove lines.  But will the stoves really be cleaner in the hands of average homeowners?
Ben Myren, owner of one of the EPA
approved test labs, is a leader in
developing cord wood testing.  Here
he starts a cord wood test at the 2013
Wood Stove Design Challenge.

The NSPS is supposed to be updated every 8 years, so theoretically there will be regular opportunities to improve the testing process.  If we can get to cordwood testing in the next 5 years, possibly the next NSPS could move to testing grams per unit of heat.  Litigation over this NSPS may bring some relief to some boiler and furnace manufacturers and others, but it may have the opposite impact on support for wood heating among civil society in general. 

Attitudes of the general public that shape policies at all levels of government, our media, the non-profit sector, etc., will have to change if wood heating is really going to be a growing renewable energy technology.  We have hosted the Wood Stove Design Challenge, with the next one scheduled for November 2018, to see if we can focus attention and resources on genuine technological advances that make stoves cleaner in homes.  Public opinion will only change when stove technology changes and stoves become cleaner not just in the lab, but also in our communities.  The 2015 NSPS alone will not get us there, for all the reasons Jim Houck outlined, but it is still possible to get there.

#    #    #

A response from Scott Nichols on boiler repeatability

Scott Nichols, owner of Tarm Biomass that distributes European made boilers sent in a response to this blog and we reproduced it below.  Scott is also on the Board of Advisors of the Alliance for Green Heat.

I agree with a great deal of what Dr. Houck wrote.  The single biggest problem with emissions from wood burning is that old stock remains in the market.  

Inherent test variability for appliances designed to burn firewood is also a problem without a doubt.
Scott Nichols has been a leader in
installing modern, automated boilers
in institutions and homes in New England.

Of course, my world is now the boiler world and the some of the testing used for boilers solves several of the problems inherent with wood stove testing.  I’ll mention some of the differences, as It may spur some ideas as you think about testing for woodstoves.  

For instance:

1)      The partial thermal storage test method is a cold to cold test, which is more indicative of both worst case and standard conditions.
2)      Boiler PM is reported in lbs/MM Btu, which eliminates the appliance size conundrum that Dr. Houck mentions at length. 


1)      Boilers very often include lambda technology, which enables the boiler to react to real time stack conditions by adjusting combustion air to optimize combustion.  Lambda technology improves cleanliness by helping the appliance to accommodate various wood moistures, volatility of the fuel, size and shape of the fuel, draft, and other factors in real time.
2)      Some regulators are already thinking about how to encourage lambda technology because they know that outside of the lab, such technology can more closely provide results as tested in laboratories.
3)      Boilers are built much more robustly than stoves and usually do not use catalysts that deteriorate over time.  They therefore tend to produce as tested results for a longer period of time. 
4)      Thermal storage allows for what is effectively single burn rate operation.  In a laboratory that can result in 4 test runs in which the boiler operates identically from run to run at full output.  This enables more comparable data for each test even though each run is weighted differently.  
5)      Round robin lab testing of one of our boilers has been underway for months.  That testing has been funded by NYSERDA.  We don’t know the final results yet, but it is important to note that people are thinking about repeatability and are putting money behind learning more.  Initial results, before we were removed from the viewing process, indicated that repeatability was a problem. 

Problems with wood boiler testing that wood stoves don’t have:

1)      Boilers are tested in room temperature laboratories.  Outdoor boilers are therefore provided an efficiency advantage because jacket heat losses in the laboratory do not reflect the real world. 
2)      Wood fuel used in outdoor boilers is always the temperature of the outdoors in the real world, not room temperature.  If you put 150 pounds of wood in a boiler and it is 10 F outside, combustion will be substantially different than if that wood is 60 F warmer in a laboratory.