Wood Doctor® Specs

Easy Rule of Thumb Solution
Once you pass the halfway mark on square footage, consider moving up to the next size of outdoor furnace. Over-kill never hurts; it will allow more time between fills. You do not want to regret buying a small unit that is maximized.

The size of an outdoor furnace must be matched to the requirements. While over-sizing is acceptable, under-sizing is not. All manufacturers use either a BTU rating or square footage capabilities. Since BTU's in wood vary, the only true way is to state maximum heating capabilities in square feet. The key word here is that the stated capability is the maximum under ideal circumstances. Here are some guidelines to follow:

Base Calculations
Start your calculations by using 75% of the stated maximum square footage. This is usually a safe place to start under most conditions. When you exceed this amount, be very careful in your calculations. Upgrade to the next size of furnace long before you reach the maximum heating capability.

Ceiling Height:
Calculations are based on having 8-ft. ceilings. If for example the ceiling height is 12 ft., then add 25% to the square footage. Also allow for any vaulted or cathedral ceilings.

Basement & Upstairs:
Add the square footage of the basement and the upstairs and any other area to be heated.

Windows:
The more windows, the higher the heat loss, so be sure to take this into consideration. Check for these features and adjust accordingly: gas filled, single pane, double glaze, triple glaze, coated glass, roof line windows, location of windows, air leaks.

Insulation:
Find out the type and R value of the insulation.

Building Age:
The older the building the less likely it is to have adequate insulation.

Geographic Location / Lot Location:
Is it on top of a cliff, out in the middle of a field, in the trees, on the shore of a lake, facing north? All of these will have a bearing.

Heating System:
Floor heating will reduce heating demand, but only if properly insulated between pad and ground. Forced air systems call for more heat.

Type of Building:
Garages, barns and shops usually take more to heat than homes. Add 25% or more on to the demand. And add another 25% more per garage door. Are the other doors insulated or single - it all adds up.

Number of Buildings:
It takes approximately 25% more to heat two 1,000 ft. buildings than it does to heat one 2,000 ft. building due to perimeter areas and underground heat loss.

Distance From Furnace to Buildings:
The longer the distance, the greater the heat loss and the larger the furnace size required.

Installation:
The use of proper and adequate underground insulation will have a bearing on the size of the furnace.