Sizing Your Furnace

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. In most parts of Canada you will not find these ideal conditions and you will be forced to estimate the capabilities. Here are some guidelines to follow:

Size of Existing Furnace

The size of the furnace existing in the house limits the number of BTU's the house can get. A 100,000 BTU furnace can only send 100,000 BTU's in to the house. Floor heating will reduce heating demand, but only if properly insulated between pad and ground. Forced air systems call for more heat.

Heating System

Properly installed in-floor heating systems help reduce heating demand and can use up to 1/2 the BTU's of forced air systems. As a rule in-floor heating systems use 15-25 BTU's per square foot per hour while forced air systems use about 50 BTU's per square foot.

Caculations

Add the square footage of the basement and the upstairs and any other area to be heated. 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.

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.

Building Age

The older the building the less likely it is to have adequate insulation. New R2000 buildings have lower heat demands on the furnace.

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 sq ft. buildings than it does to heat one 2,000 sq 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. The use of proper and adequate underground insulation around your supply lines from the furnace to the building will help minimize the loss of heat.