How To Purchase An Outdoor Wood Furnace

Outdoor wood furnaces are springing up everywhere. Each year there are more and more manufacturers, and each claims to have the best product available. But which one really is the best?

All outdoor wood furnaces work. There is no such thing as a cold fire. All outdoor wood furnaces produce heat and lots of it. However, all outdoor wood furnaces are not alike.
Outdoor wood furnaces are a major cost; even the “cheapies” are a significant investment. The key word here is investment.

The key decision is whether to make an investment or merely a purchase. Before buying, consider performance, quality, safety and above all, longevity.

Check into the following BEFORE you make your investment:

  • LENGTH OF CHIMNEY
  • CHIMNEY LOCATION
  • CHIMNEY CAPS
  • FURNACE DOOR INSULATION
  • DOOR ANTI-BLOWBACK CATCH
  • TYPE OF DOOR GASKETS
  • TYPE OF DOOR CONSTRUCTION
  • SIZE OF DOOR
  • INSULATED, CAST or WATER-JACKETED DOORS
  • LEGS vs SKIRTING
  • RUST CONTROL
  • LONGEVITY OF STAINLESS STEEL
  • ANTIFREEZE AS A RUST INHIBITOR
  • FREEZE PREVENTION
  • WEIGHT OF STEEL
  • INSULATION TYPES
  • WATER JACKET LOCATION
  • OUTSIDE WATER JACKET
  • SIZE OF WATER STORAGE
  • HEATING CAPACITY
  • EFFICIENCY
  • FLOOR HEATING vs FORCED AIR or PASSIVE
  • HOOKING INTO AN EXISTING PRESSURE SYSTEM
  • TYPE OF WATER PIPE
  • CREOSOTE
  • DEPTH OF FIREBOX
  • ASH REMOVAL
  • SAFETY FEATURES
  • COMPONENT REPLACEMENT
  • WOOD CONSUMPTION
  • WATER EXPANSION
  • HOUSING
  • DRAFT CONTROL–MANUAL, ELECTRIC, FORCED AIR
  • STRENGTH
  • CONTROLS
  • TESTING

Firewood Facts – Burning the right wood

Measurement of Wood

A standard cord of wood has a volume of 128 cubic feet and is 4 feet high, 4 feet wide and 8 feet long. Face cords, or short cords, do not have standard measurements and volumes cannot be determined; thus this term should not be used to purchase wood.

Number of Trees Required to Yield One Standard Cord

Diameter of Tree Measured at Chest Height  Deciduous Coniferous
7 15 20
8 11 13
9 8 10
10 5 8
12 4 6
14 3 3.7
16 2 2.5
18 1.5 1.9

 

Heating Value of Wood

When burning wood it is essential to have the wood as dry as possible in order to produce more heat per pound of fuel, thereby obtaining a higher heat value and also reducing trouble with creosote.

Air-dried wood contains approximately 20% moisture and will yield about 5,800 BTU’s per pound. Green wood containing about 60% moisture will yield only 4,100 BTU’s per pound. The heavier the weight of dry wood, the more BTU’s per cord.

Heating Value per Air-Dried Cord in BTU’s

White Oak 30,600,000 Poplar 17,260,000
White Elm 24,500,000 White Pine 17,100,000
Tamarack 24,000,000 Basswood 17,000,000
White Birch  23,400,000 White Cedar 16,300,000
Black Ash  22,600,000 White Spruce 16,200,000
Manitoba Maple  19,300,000  Balsam Fir 15,500,000

Seasoning Wood

Wood is considered seasoned when the moisture content is 20%. The diameter makes a big difference with respect to drying. To ensure uniform rapid seasoning, pieces over 8″ should be split once and those pieces over 12″ should be quartered.

Wood cut during the fall and winter and piled in the open should be well-seasoned and ready for burning the following winter. Unsplit wood requires 9 to 12 months to season thoroughly. The moisture content of split wood will be reduced to about 35% in three months’ time, if dried during the late spring and summer months. This wood has 86 to 90% as much heating value as wood of the same species that is thoroughly seasoned. Fresh cut wood has a heating value of around 70% of that of seasoned wood.

Therefore the value of thoroughly seasoned wood will offer significantly greater heating value. In addition, seasoned wood is lighter to handle and causes a lesser problem with respect to creosote. Even though an outdoor furnace equipped with a forced air draft fan will easily burn green wood, it is not recommended due to creosote and lack of heat.