No matter what you do, when it is 68° F inside your house, and 0 degrees outside your
house; the cold will suck the heat out of your house. It will pull at a certain rate through
the exposed walls and ceilings, through the windows and floors. This is known as heat transfer.
The cold air is also trying to sneak into the building through every little crack in every
nook and cranny. This is known as infiltration. Your heat, on the other hand, is trying
to escape through every nook and cranny. This is known as exhilation. It's as if the house
was breathing. Breathing both air and temperature in and out.
The total of all this leaking and losing at a specific low temperature for your region,
is known as the heat loss. This total will be calculated in btu's per hour, and the heating
system will need to produce and distribute this same amount of btu's per hour to maintaint
your 68° F room temperature. As most rooms differ from one another, each room's heat
loss must be determined. The total loss of all rooms added together will determine the size
and design of the heating system.
In simple structures, the mere replacement of this lost heat is sufficient; but in complex
houses with open floor plans and multiple levels, the flow of heat within the building becomes
a factor. Heat rising from the first floor to the second, increases the demand on the first
floor while decreasing the demand on the second.
The formula used here is a combination of three ingredients developed to reflect the internal
conditions of a modern structure. It combines industry accepted standards of heat transfer
with the old fahioned tin knocker "cfm method" of computation ; blended together
by 25 years experience designing and installing heating and cooling systems. The result
is an estimate of comfort.
In the heat loss calculation, all windows are created equal, no matter which direction
they face. Disallowing for wind factors, similar types of glazings lose heat at the same
rate. On the other hand, when calculating heat gain, windows facing east and west gain more
heat that those facing north and south. This results in larger quantities of air being distributed
to rooms with east and west facing windows. This air is necessary for cooling but not for
heating. In the more northern climates, where heating is a priority, enter all window areas
as east and west shaded, regardless of which direction they
face. This will restore the emphasis on a balanced distribution system rather than one weighted
toward solar radiation.