Dartmouth College was planning to replace the existing oil-fired central steam heating plant with a tree-burning hot water heating plant.

Dartmouth College held several public meetings during which there were numerous objections from nearby residents regarding the up to 16 eighteen-wheelers per day delivering wood chips, and regarding the harmful air pollution of the plant.

Dartmouth College present and former environmental professors also were opposed to the wood-burning plant. They recommend ground source heat pump systems, similar to those in use at various progressive universities, such as Ball State University, which has a campus wide GSHP system that began full operation in 2015.

Dartmouth College has, for all practical purposes, abandoned the tree burning plant that would have lasted for at least 35 years!

Dartmouth College is implementing ground source heat pump systems.

What About Those Particulate Emissions?

Dartmouth College claimed the wood burning plant would be very efficient and have very low particulate emissions.

The below comparison shows the likely PM2.5 emissions of the proposed Dartmouth College wood-burning boilers would be equivalent to 351 high-efficiency, wood-fired, household stoves at one point.

Wood Burning Household Stoves 

The emissions of EPA-certified wood burning stoves are tested under laboratory conditions. The testing bear only a passing relationship to how the stoves are used in the real world.

Method 28 requires the use of wood fuel that has a moisture content (wet basis) of 16 – 20%.

Method 28 requires testing under 4 different burn rates, not just at the rated output.


NOTE: All that during a test burn of several hours, conducted by experts, at steady conditions, in a laboratory, with a prepared fuel sample. Real-world emissions likely would be 2 to 3 times greater.

Studies have shown the performance of EPA-certified wood stoves, especially with catalytic reactors, deteriorate over time.

Thus, the wood stove test data reflect a ‘best case scenario’ of new stove performance under laboratory conditions.

Natural gas and propane fuels, defined by ASTM standards, burn much more cleanly than wood, leading to near-zero particulate emissions. See Appendix.

Wood is largely undefined. It has varying quality, composition and water content leading to varying burn rates and varying particulate emissions.

EPA PM10 Emissions Limits: The EPA mandated PM10 smoke emission limit for wood stoves is based on heat output, a more rational basis than heat input, as it rewards stove efficiency.

Step 1, 4.5 g/h, in effect at present

Step 2, 2.0 g/h, will take effect on May 15, 2020

Table 1 shows a wood stove with an output of 50000 Btu/h (sufficient for a well-insulated/well-sealed 2000 sq ft house in New England), at 80% efficiency, could achieve emissions of 2 g/h, if the flyash portion of the ash is 15.2% or less of the total ash content of the wood; 84.8% would be in the bottom of the stove. The excess air would be 15 to 20 percent.

The table shows a wood stove with an output of 50000 Btu/h (sufficient for a well-insulated/well-sealed 2000 sq ft house in New England), at 50% efficiency, could achieve emissions of 8.5 g/h, if the flyash portion of the ash is 40.2% or less of the total ash content of the wood; 60.8% would be in the bottom of the stove. The smoke emissions of such a stove would be about 2.65 times greater than of the 80% efficient stove, although dilution, due to about 40% excess air, might make the smoke look less dense.

NOTE: All that during a test burn of several hours, conducted by experts, at steady conditions near rated output, in a laboratory, with a prepared fuel sample. Real-world emissions likely would be 2 to 3 times greater.

NOTE: For rating purposes, the EPA uses 8600 Btu/lb of dry wood. Manufacturers of wood stoves aim to have test fuels as close as possible to that value. This would not be the case in the real world.



Click to access strategies.pdf

Table 1/Fuel inputEPA-certifiedEfficiencyHeat outputFlyash fractionAllowed PM10 emission
100000July I, 198850500000.4028.5
90909July I, 199055500000.3917.5
76923May 15, 201565500000.2774.5
62500May 15, 202080500000.1522.0
Ash content, %, dry0.40
HHV, Btu/lb, dry8600

The emissions for the 80% efficient stove would be 1000000/50000 x 2.00 = 40 g/million Btu, or 0.0881 lb/million Btu, based on heat output, or 0.0881 x 50000/62500 = 0.0705, based on heat input. See table 2

Table 2/Conversion of g/h to lb/million Btu
Stove output, Btu/h50000
Stove input, Btu/h62500
g/million Btu40
lb/million Btu (heat output)0.0881
lb/million Btu (heat input)0.0705

Heat delivered could be added to:

1) A hot water circulating loop

2) A warm air circulating loop

3) An open-floorplan space

Dartmouth College Biomass Boiler

Medium-size hot water boilers to heat a college campus, with air pollution control systems, are allowed to have PM2.5 emissions of 0.035 lb/million Btu, but typically have less than 0.020 lb/million Btu, based on heat input. See URL page 1.6-6

Click to access c01s06.pdf

The Dartmouth College biomass boiler has:

A heat output of 54.6 million Btu/h.

A heat input of about (54.6 x 10^6 x 1/0.7, seasonal efficiency) = 78.0 million Btu/h

A heat input about (78.0 x 10^6) / (62.5 x 10^3) = 1248 times greater than the heat input of the 80%-efficient wood stove in table 1.

The Dartmouth boiler would have PM2.5 emissions of about 78.0 million Btu/h x 0.02 lb/million Btu = 1.5600 lb/h, based on heat input.

The 80%-efficient wood stove would have PM10 emissions of 62500/1000000 x 0.0705= 0.00445 lb/h, based on heat input. See table 2 and 3.

Wood Stoves Equivalent to Dartmouth Biomass Plant: The Dartmouth biomass plant emissions would be equivalent to 1.5600/0.0044 = 351 high-efficiency, wood-fired, household stoves at one point. See table 3.

Table 3/PM2.5 Emission EquivalenceOutput, Btu/hInput, Btu/hHeat input basisPM2.5 emissions
Btu/hBtu/hlb/million Btulb/h
Dartmouth Biomass54600000780000000.02001.5600
Efficiency0.7PM10 emissions
Household wood stove50000625000.07050.00445


Heat Loss due to water vapor produced by burning hydrogen

2 lb H2 + 16 lb O2 —> 18 lb H2O

Carbon in 100 lb of dry wood is 48 lb

Hydrogen in 100 lb of dry wood is 6 lb

0.06 lb H2 + 0.48 lb O2 —>  0.54 lb H2O

Heat of vaporization is 1058.2 Btu/lb water

Evaporation loss = 0.54 x 1058.2 = 570 Btu/lb*

LHV = 8600 – 570 = 8030 Btu/lb, dry

* Excludes heat loss from fuel inlet temperature to chimney outlet temperature.

That heat loss disappears via the chimney. Thus, the maximum possible boiler efficiency could be 8030/8600 = 93.4%, if all other losses were ignored. See Appendix of URL


Real World Conditions

Dartmouth: Dartmouth College would have a certificate stating the allowed PM2.5 emissions are 0.035 lb/million Btu, based on heat input, and the tested emissions, when the boiler was new, were 0.020 lb/million Btu., based on heat input. The chimney would visually show only condensed water vapor.

However, during the year, ambient temperatures and building heating loads would vary from hour to hour each day; the fuel, trucked in from as far away as 90 miles, would have varying quality, composition and water content; and the plant would be aging. Those factors would cause the plant to become less efficient and the PM2.5 emissions/million Btu to significantly increase. Yet, it is likely, the chimney would visually show only condensed water vapor.

If a short chimney, to reduce visual impact, the dispersion of flue gases would be near zero during wind-still conditions, which frequently occur at night throughout the year; smoke would stay near the ground. If a tall chimney, say 150 ft or more, there would be greater dispersion.

Households: The metal “hang tag” on the household stove would state EPA-certified PM10 emissions at 2 g/h or less, based on heat output. However, the household people operating the stoves are not the experts performing the EPA certification tests. The household people likely would feed the stove, on an irregular basis, with whatever quality cordwood/wood pellets they could obtain. The cord wood may not be as dry as recommended, etc. Also, the emissions/million Btu would be significantly greater during start-up and burn-down operation, which could occur each day.

Summary: The new boilers at Dartmouth and households likely would have 50 to 100 percent greater emissions than the test values. Only time would tell if the noses of people living near the Dartmouth plant would become sufficiently irritated to cause complaints. The Dartmouth plant is planned to be at the location for about 35 years.


Old Wood Stoves versus New Wood Stoves

Old wood stoves, pre-1990, not EPA-certified, have seasonal heating efficiencies of about 50%, and have real-world PM10 particulate emissions of about 20 – 40 g/h, i.e., they are dirty smokers!

New wood stoves, EPA-certified, have seasonal heating efficiencies of about 75%, and have, under carefully proscribed laboratory conditions, PM10 particulate emissions of less than 4 g/h at present, and less than 2.0 g/h after May 15, 2020. Relatively few wood stoves, foreign and domestic, would meet the 2020 requirements.

On average, their real-world emissions likely would be at least double those values, due to daily start-ups and burn-downs, variations in wood quality, variations in stove cleanliness and other maintenance, etc.

Technological advances have improved real-world seasonal efficiencies by about 50%, and reduced real-world emissions from about 20 – 40 g/h in 1990 to about 4 g/h or more, in 2020.


Larger Wood Burning Plants

Wood chip moisture content is about 45% to 50%, as delivered to the boiler. 

The wood chips are fed onto a travelling grate. They are dry after a few feet of travel.

The EPA testing method for larger biomass boilers is extremely detailed, trying to cover all the bases to avoid cheating by manufacturers.

The EPA PM2.5 emissions are “based on heat input to boiler” for medium and larger capacity boilers.

The EPA has been trying to have it “based on heat output from boiler”, as that would reward efficiency. The industry is opposed, because it would make their boilers look “dirtier”.

Residential Wood Burning Appliances

The EPA PM10 emissions are “based on heat output of the stove, or hot water boiler” for residential wood burning appliances, a more rational basis than heat input, as it rewards boiler efficiency


Particulate Emissions of Wood-Burning Appliances


– In the 70s airtight air-heating cordwood stoves and water heating furnaces emitted about 40 grams/hour of PM10

– Per EPA, all wood stoves manufactured after July 1, 1988 must emit less than 8.5 g/h (5.5 g/h, if catalytic type). Existing inventories of non-approved wood stoves may continue to be sold until 1990.

– Per EPA, all wood stoves manufactured after July 1, 1990 must emit less than 7.5 grams/h (4.1 g/h, if catalytic type). Existing inventories of non-approved wood stoves may continue to be sold until 1992.

– Per EPA, all wood stoves manufactured after May 15, 2015 must emit less than 4.5 g/h. Existing inventories of non-approved wood stoves may continue to be sold until December 31, 2015

The 2015 revision also includes several types of biomass heaters which were previously exempt: pellet stoves; indoor and outdoor wood-fired hot water heaters; wood-burning forced-air furnaces; and a type of previously unregulated wood stove known as single burn-rate stoves. 

– Per EPA, all wood stoves manufactured after May 15, 2020 must emit less than 2.0 g/h. Existing inventories of non-approved wood stoves may continue to be sold until December 31, 2020

This final phase would lower the emissions limit to 2.0 g/h as measured by existing test protocols using dimensional lumber “cribs”, or 2.5 g/h as measured by a still-in-development procedure using cordwood.




Table 4/TypeDatePM10, g/hPM10, g/h
Wood stoveJuly 1,19888.55.5, if catalytic
Wood stoveJuly 1,19907.54.1, if catalytic
Wood stoveMay 15, 20154.5EPA step 1
Wood stoveMay 15, 20202.0EPA step 2


Pellet Furnaces versus Fuel oil, Natural Gas and Propane Furnaces

Pellet furnaces, EPA-certified, are a major improvement over fireplace inserts.

However, their pollution is far worse than of furnaces burning low sulfur fuel oil, natural gas, and propane. See below sections.

Having near-zero net energy buildings, instead of energy-hog buildings, would greatly reduce any burning.


Burning the Clearcut Harvest for Heating and Generating Electricity in Vermont

People often say: Burning wood is renewable and the CO2 should not be counted, because it is absorbed by new tree growth.

All that is true, but when would the CO2 be absorbed by new tree growth?

Burning wood adds carbon dioxide to the atmosphere.

That carbon dioxide is removed from the atmosphere, only if the forests regrow and keep that carbon sequestered in biomass and soils.

Regrowth takes time.

Regrowth is not certain. Fire, insect damage, additional harvesting of the same area, or forest conversion to other uses (e.g., agriculture, development, recreation, such as skiing) will limit or prevent biomass regrowth and thus reduce carbon absorption. See MIT article in this URL


Burning the Clearcut Harvest in Year 1: If our clearcut harvest had been burned in year 1, the combustion CO2 would start its absorption in year 1 + 35 = 36, after its 35-y “C neutrality” period. See note.

C release due to biomass decay would still be ongoing for about 55 years after year 35. 

Ourcombustion CO2 would just hang around in the atmosphere until the time of its absorption. 

All the other sinks already are busy absorbing other CO2. 

No spare sink is available for ourCO2. 

Ourcombustion CO2 cannot push other CO2 aside by claiming a holier than thou pedigree.

Ourcombustion CO2 needs to be absorbed by ournew tree growth, so ourwood burning can be claimed to be “renewable”.

Year 2: The combustion CO2 of year 2 would have its own clearcut area, with new tree growth, and NEP, etc., and would start its absorption in year 2 + 35 = 37, its “C neutrality year”. 

Year 40: The useful service life of a woodchip plant usually is (very optimistically) about 40 years. The CO2 of year 40 would start its absorption in year 40 + 35 = 75, its “C neutrality year”. 

Time Period to Absorb Our Combustion CO2 in Vermont

Carbon is about 50% of wood, by weight. 

A standing forest is about 50% water, by weight

The Vermont aboveground carbon was 72.53 metric t/ha, in 2015, latest numbers per USFS. See table 2

Wood chips for combustion would be {73.53/(0.5 x 0.5)} x 0.85 = 250 metric t/ha (or 101.17 metric t/acre), if 85% of all aboveground biomass were removed. 

The rest (slash, underbrush, dead wood, etc.) would be left to decay on the forest floor.

Combustion CO2 emissions are about 1.0 metric t/metric t of as-harvested (wet) wood chips.

Combustion CO2 emissions would be about 250 metric t/ha

In Vermont, the absorption period of our combustion CO2 would be about (250 metric t/ha) / (2.421 metric t of CO2/ha/y) = 103 years. See table 1 

Remember, the absorption of our combustion CO2 would start after the “C neutrality period”.

NOTE: If Vermont had planted/fertilized/managed forests the 2.421 would be greater, say 3.0, and the absorption period would be shorter, but the below category “Additional CO2 emissions” would be higher. 

There would appear to be a free lunch, if “Additional CO2 Emissions” were ignored, as is often the case. 

See next paragraph.

Additional CO2 Emissions not Related to Burning Wood

CO2 emissions occurred due to tree stand maintenance, fertilizing, harvesting, cutting, chipping, pelletizing and transport, about 10%, if burning wood chips, about 15%, if burning wood pellets

CO2 emissions also occurred due to setting up and maintaining in good working order the A to Z logging sector infrastructure. 

CO2 emissions also occur due to operating the heating or power plant and, if applicable, its hot water/steam distribution system

That CO2, not related to forest regrowth and combustion, should be counted, just as any other CO2. 

Very often that CO2 is simply ignored.


Vermont, and likely other NE states, has been losing forest area since 2000 due to logging and encroachments. See URL

Click to access ru_fs164.pdf


Comparison of Non-Certified and EPA-Certified Furnaces

Here is an example of an EPA-certified pellet furnace, which complies with the 2.0 g/h required by EPA by May 15, 2020.

On a cold day, at a fuel input of 62,500 Btu/h, and an efficiency of 80%, it would deliver 50,000 Btu/h to a standard 2000 sq ft house in upstate NY, or VT, or NH, etc., and emit PM10 of about 48 g/day. See bold values in table 2.

A pre-1988, uncertified cordwood furnace would emit about 10 times more than the example pellet furnace.

Table 5Not certifiedEPA-certifiedEPA-certifiedEPA-certified
PhasePhase IPhase IIPhase II
Furnace typePre-1988 cordwoodCordwood/pelletCordwood/pelletPellet 
Fuel heat inputBtu/h100000769236250062500
Pollution/hPM10, gram/h20.
Pollution/dPM10, gram/d4801084848
Heat outputBtu/h50000500005000050000


Test Results of Residential Water Heating Boilers and Air Heating Furnaces

Here are some results of PM and efficiency testing of various heating units, using various fuels, performed by engineers of the Brookhaven National Laboratory and the EPA. See URL

Click to access 71376.pdf

PM10 Tests: The PM emissions were based on MJ of fuel input. The results of the tests were:

1) Gas-fired units have the lowest PM emissions averaging 0.011 to 0.016 mg/MJ

2) Regarding fuel oil units:

– Ultra low sulfur fuel-oil-units have PM emissions of 0.025 to 0.060 mg/MJ

– Low sulfur fuel-oil units have PM emissions of 0.49 to 0.510 mg/MJ

– Typical sulfur No-2 fuel-oil units have PM emissions of 1.320 to 2.100 mg/MJ

3) Pellet stoves have PM10 emissions of about 25 mg/MJ; even the cleanest ones in 2020 would be off the charts dirtier than all fuel oil and gas units, i.e., about 1852 times worse than gas. See table 6.

NOTE: Cordwood stoves were not tested.

Older cord wood stoves have about 5 times the PM and PAH of EPA-certified pellet stoves.

New cord wood stoves, EPA-certified, have about 2 times the PM and PAH of EPA-certified pellet stoves.

Table 6/ Household ApplianceHot water boilerWarm air furnaceTimes worse than gas
Particle size PM10 and smaller PM10 and smaller 
Natural gas0.0160.0111.0
ULS fuel oil, 15 ppm0.0250.06014.6
LS fuel oil, 500 ppm0.4900.51050
No. 2 fuel oil, 2000 ppm1.3202.100588
Wood pellet; 3-stove average25.00025.0001852


Carbon Content of Wood: The carbon contents in heartwood of softwood and hardwood species were determined. C in kiln-dried hardwood species ranged from 46.27% to 49.97%, and in conifers from 47.21% to 55.2%. Heartwood is the older harder non-living central wood of trees that is usually darker, denser, less permeable, and more durable than the surrounding sapwood.


The average higher heating value, HHV, of the more resinous softwoods is about 9,000 Btu/lb of dry trunk wood, and for the less resinous hardwoods about 8,300 Btu/lb of dry trunk wood. The EPA selected an average value of 8600 Btu/lb of dry trunk wood.

Wood Chips for Burning: Wood chips are made from whole trees that are fed into very large chippers. It is a noisy sight to behold. A large crane grabs an 18-inch diameter tree, feeds it horizontally into the big hopper, and within about a minute the entire tree has become wood chips that are blown into a 40 ft trailer!!! The trees are low quality trees, and often are misshapen, sickly and dead trees.

Whole tree wood chips consist of about 50% carbon and about 6% hydrogen, and have a typical heat content of 4785 Btu/lb at 44% moisture content, or 4785 / (1 – 0.44) = 8545 Btu/lb, HHV, dry. See URLs

CO2 emissions of wood, per EPA, are (1000000/8600, HHV) x 0.50, C fraction x 44/12, mol. wt. ratio = 213.18 lb/million Btu.

CO2 emissions of dry wood chips, per BERC, are (1000000/8545, HHV) x 0.50, C fraction x 44/12, mol. wt. ratio) = 214.6 lb/million Btu



Click to access 274491.pdf


The 44/12-molecular weight ratio is calculated as follows:

The combustion equation is C + O2 –> CO2. 

Molecular weight of CO2 = 12 lb C + 32 lb O2 = 44 lb, or

12/12 ton C + 32/12 ton O2 = 44/12 ton CO2

Click to access WDBASICS.pdf

NOTE: The higher heating value, HHV, is determined with a calorimeter in a laboratory. Fuel is fed in at 59F and combusted with pure oxygen, i.e., no excess air, until combustion is complete. Heat is extracted from the products of combustion, which could be 500F, to reduce their temperature to 59F. Any water vapor due to combustion of hydrogen in the fuel, 2 H2 + O2 -> 2 H2O, is condensed and cooled to 59F. The laboratory tests are performed with pure oxygen to achieve near 100% completion of reactions. Such measurements often use a standard fuel temperature of 15C or 59F. Needless to say HHV is a fantasy number, as far as the real world is concerned. See URLs.



NOTE: The lower heating value, LHV, is determined during laboratory tests by subtracting the heat released due to condensing the water vapor, i.e., LLV = HHV – condensation heat released.


Approximate Composition of Woodsmoke, by weight %. See URL page 14

Click to access rwc_pm25.pdf

The more-efficient stoves would burn more CO and methane and likely would use a lesser percentage of excess air during steady burn mode.

The ashes in the bottom of the stove usually contain various unburnt carbon compounds; the grayer and finer the ash, the less carbon.

Table 7/Woodsmoke composition%, by wgt%, by wgt
– Organic compounds90.0
– Elemental carbon10.0
– Inorganic compounds<1
Volatile organic compounds0.1
– Methane50.0
– Other organic compounds50.0


Old Inefficient Stove vs New Efficient Stove

Older stove:

Air inlet, not pre-warmed, reduces combustion

Primary combustion chamber

Gases cool in the flue before they have a chance to fully combust, forming smoke and creosote

Newer stove:

Pre-warming chamber heats combustion air

Primary combustion chamber

Secondary combustion air is introduced above the fire

Extra chamber increases time for the gases to combust

Catalytic converter breaks down any remaining hydrocarbons, releasing more heat

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