Impacts of wood species and moisture content on emissions from residential wood heaters

Figures & data

Figure 1. Crib wood species total PM (a) emission factors (g/kg) and (b) emission rates (g/h) (Hearthlab Solutions 2017).

Table 1. Characteristics of cordwood stoves used for species and moisture tests.

Stove #	Construction Type	Firebox Size	Emission Controls	EPA Certification
Stove 6	Steel	2.2 ft^3 (0.062 m^3) Medium	Non-catalytic tube	Step 1
Stove 7	High mass*	1.9 ft^3 (0.054 m^3) Medium	Hybrid – catalytic and non-catalytic	Step 2
Stove 15	Steel	0.8 ft^3 (0.023 m^3) Small	Non-catalytic tube	Step 2
Stove 23	Cast iron	1.8 ft^3 (0.051 m^3) Medium	Non-catalytic, optional catalyst	Step 2 (with and without catalyst)

*High mass stoves are designed to trap heat and release it slowly into the building’s living space. The thermal storage is usually provided by a large mass of a dense material.

Table 2a. Cordwood stove species tests.

Stove	Protocol	Species
6	ASTM E3053	Red Maple Red Oak
		Beech
6	IDC	Red Maple
		Red Oak
7	IDC	Red Maple Red Oak Spruce
		Poplar
15	IDC	Red Maple Red Oak
		Beech

Table 2b. Tests evaluating impact of MC (%, dry basis) on cordwood stove performance.

Stove	Protocol	Species	Dry Mean	Dry SD	Wet Mean	Wet SD
6	IDC	Red Oak	21.4	0.5	28.1	0.2
7	IDC	Red Oak	21.2	0.4	28.7	0.3
23-No cat	IDC	Red Maple	21.1	0.3	27.0	0.7
23-cat	IDC	Red Maple	21.2	0.1	27.2	0.6

Figure 2. Distribution of MCs in fuel pieces used in moisture experiments (error bars represent 95% confidence intervals).

Table 3. Summary of IDC cordwood protocol.

Segment	Fueling and Operating Parameters
Start-up	Cold Start, kindling density – 1 lb/ft^3 (16 kg/m^3) max, starter fuel-3 lb/ft^3 (48 kg/m^3) Air fully open. Burn 75% of load, by weight.
Reload 1 High-fire	Load density – 7 lb/ft^3 (112 kg/m^3), small cordwood pieces, random loading pattern. High air setting. When 50% is burned, switch to lowest air setting. Burn 90% of load.
Reload 2 Maintenance	Load density – 5 lb/ft^3 (80 kg/m^3), random loading pattern. Lowest air setting. Burn 90% of load.
Reload 3 Overnight	Load density – 12 lb/ft^3 (192 kg/m^3), mix of small and large cordwood pieces, loaded in one direction to maximum volume. Lowest air setting. Burn 90% of load.

Table 4. Pellet composition and tests.

Pellet#	Pellet Type	MC%	Ash %	Number of Tests per Stove
				Stove 10	Stove 11	Stove 13	Stove 14
1	Eastern White Pine	3.3–4.2	0.21	1	1	3	1
2	Douglas Fir	5.6–6.2	0.30	1	1	1	1
3	Douglas Fir	2.3–3.1	0.16	3	1	1	1
4	Hardwood	5.0–5.9	0.50	3	1	1	1
5	Hardwood	4.8–5.8	0.48	1	1	3	1
6	Hard-soft Mix	4.2–5.0	0.52	1	1	1	1
9	Douglas Fir	6.8	0.23	3	0	3	0

Table 5. Effect of fuel MC on emissions and efficiency – mean [range].

Stove	Fuel	Emission Rate (g/h)	Emission Factor (g/kg)	Overall Efficiency (%), HHV basis
6	Seasoned Oak (21%)	13.4 [10.4–17.1]	6.9 [5.2–8.9]	61.6 [61.0–62.6]
	Wet Oak (28%)	34.1 [26.7–41.2]	18.0 [13.7–22.4]	57.1 [56.8–57.5]
7	Seasoned Oak (21%)	2.2 [1.4–3.3]	1.4 [0.9–2.1]	68.8 [67.8–69.9]
	Wet Oak (29%)	3.4 [2.6–4.7]	2.4 [1.9–3.1]	67.9 [67.8–69.5]
23 No Cat.	Seasoned Maple (21%)	7.6 [4.9–11.4]	8.2 [2.7–13.6]	60.8 [55.2–66.1]
	Wet Maple (27%)	4.9 [2.9–6.4]	3.1 [1.6–4.3]	63.2 [60.4–66.2]
23 Cat.	Seasoned Maple (21%)	4.0 [2.7–6.1]	2.5 [1.7–3.5]	n/a
	Wet Maple (27%)	5.5 [3.5–8.7]	4.4 [1.9–7.6]	n/a

Figure 3. (a) Comparison of PM emission rates (g/h), (b) emission factors (g/kg) and (c) HHV efficiencies (%) in wet and dry fuel (average, minimum, and maximum).

*Stove 23 Cat efficiency available for only one run with each fuel type.

Figure 4. Comparison of Stove 6 (a and b) and Stove 7 (c and d) wet and properly seasoned (dry) wood emission rates and emission factors by IDC phase (average, minimum, and maximum).

Table 6. Stove 6 ASTM E3053 PM emission rates (g/h) by fuel species.

	High Burn Phase	Medium Burn Phase	Low Burn Phase
Maple	2.4	4.8	4.6
	14.6	n/a	n/a
Oak	9.7	6.7	9.8
	4.0	n/a	n/a
Beech	3.3	5.5	7.3
	3.0	n/a	n/a

Figure 5. IDC runs with different fuel species for Stoves 6, 7, and 15: (a) PM emission rates, (b) PM emission factors, (c) HHV efficiencies (average, minimum, and maximum).

Figure 6. (a) PM Emission rates and (b) emission factors by stove and pellet (where available, error bars indicate minimum and maximum).

Figure 7. Stove 11, 15-minute running average TEOM PM rate with soft and hardwood pellets.

Figure 8. PM EF vs. pellet ash content for three soft and three hardwood pellets.

Hearthlab Solutions. 2017. Wood species testing using crib and cordwood in a pre-NSPS residential wood heater. EPA Contract No. EP-D-12-001. Accessed April 1, 2021. https://www.nescaum.org/documents/epa-hq-oar-2016-0130-0010-1.pdf/

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Data availability statement

The data that support the findings of this study are available from NESCAUM upon reasonable request to NESCAUM’s Executive Director.