Global Hydronics Outdoor Furnaces, Wood Furnaces, Coal Furnaces, Boilers, Coal Stokers

The type of wood burned, whether hardwood or softwood, is important for energy efficiency.

Hardwoods have less resin and burn slower and longer. Softwoods burn quickly. In addition to the type of wood, the seasoned length of the wood influences the fuel efficiency. Seasoning the wood refers to the allowed drying time before burning. Moisture reduces the wood's fuel value and wood needs to be dried at least 4 to 6 months before used.

Species	Density (lbs per cubic ft)	Weight Per Cord (lbs)	BTU's Per Cord (millions)	Recoverable BTU's per Cord (Millions)	Units needed to produce 1 Million BTU's
Apple	48.7	4100	26.5	18.55	0.054
Aspen	27	2290	14.7	10.29	0.097
Balsam Fir	26.3	2236	14.3	10.01	0.10
Basswood	24.8	2108	13.5	9.45	0.106
Beech	44.2	3757	24	16.8	0.060
Black Ash	35.2	2992	19.1	13.37	0.075
Black Spruce	29.2	2482	15.9	11.13	0.090
Box elder	32.9	2797	17.9	12.53	0.080
Cherry	36.7	3121	20	14	0.071
Cottonwood	24.8	2108	13.5	9.45	0.106
East Hop Hornbeam	50.2	4267	27.3	19.11	0.052
Elm	35.9	3052	19.5	13.65	0.073
Hackberry	38.2	3247	20.8	14.56	0.069
Hemlock	29.2	2482	15.9	11.13	0.090
Hickory	50.9	4327	27.7	19.39	0.052
Jack Pine	31.4	2669	17.1	11.97	0.084
Norway Pine	31.4	2669	17.1	11.97	0.084
Paper Birch	37.4	3179	20.3	14.21	0.070
Ponderosa Pine	28	2380	15.2	10.64	0.094
Red Oak	44.2	3757	24	16.8	0.060
Red Maple	34.4	2924	18.7	13.09	0.076
Sugar Maple	44.2	3757	24	16.8	0.060
Tamarack	38.2	3247	20.8	14.56	0.069
Yellow Birch	43.4	3689	23.6	16.52	0.061
White Ash	43.4	3689	23.6	16.52	0.061
White Oak	47.2	4012	25.7	17.99	0.056
White Pine	26.3	2236	14.3	10.01	0.100