Homes with duct work leak up to 25 per cent more air than homes without such a system, according to some experts. Thus, a home with duct work may use 25 to 40 per cent more heating and cooling energy.
The reason is that an air moving system creates pressure differences within the house as well as in the duct work itself. In addition to normal leaks, the pressurization draws outside air into crawl space ducts, forces air out through cracks in the house shell and in the supply ducts, or pulls outside air in through cracks in the house shell and in the return ducts.
To get a warm-air system to work efficiently, make sure that the house shell and all the ducts that pass through unheated spaces are properly sealed. Also, be sure that there are enough return ducts for your system. If all return air comes from one location or if the house has two stories and no return duct from upstairs, add another return duct.
You can distinguish between supply and return ducts by touch when the furnace is on as supply ducts feel warm while return ducts feel cool.
Adjusting a blower switch: Ignition of the burner starts a new cycle, but useful heat is delivered only when the blower operates. You can save on your heating bill by setting the fan to come on earlier in the cycle and to run longer after the burner shuts off.
Take the cover off the blower switch on the side of the furnace, and shift the lowest of the three set points (fan off) down slightly, lower the middle set point (fan on) by exactly the same amount and then run the furnace through a test cycle.
Adjusting the blower speed: Increasing the speed of a furnace’s blower may boost heat distribution, or it may worsen the problem — try it and see.
You can adjust a belt-driven model to increase the speed of the fan. To do this, normally the pulley on the motor would be larger than the pulley on the fan. It is best to leave these adjustments to a certified heating and cooling contractor.
Balancing heat distribution: To provide even heating, adjust the dampers in the supply registers or the dampers in the ducts so that each room receives sufficient heat relative to its size and exposure. Also, make sure that the amount of return air to the furnace fan is equal to the amount of air being delivered to the rooms.
This can be attained by installing wall registers near the floor just above the baseboard and ducting the return air register to the basement or crawl space, and then tying it into the main return-air duct going to the furnace.
Every room of the house, with the exception of the bathroom, should have a return air. The bathroom should be vented by a ceiling fan, controlled by a variable-speed switch. The venting pipes from the ceiling fan to the underside of the roof in the attic should not be metal but should be a Micro-Air-Duct.
This duct pipe is made from compressed fibreglass covered with an exterior foil coating. The pipes are made in sections of 24 and 36 inches. Ends of each section are made in such a way that the end of one pipe will fit inside the end of the next pipe. All joints should be sealed by using a foil tape with an adhesive back made specifically for this purpose.
Never vent any ceiling exhaust fan into the attic. It must be vented through the attic and out the roof or through an outside wall. There should be a spring loaded-back draft damper over the outside end of the pipe that will close as soon as the fan switch is turned off. This devise is made especially for this purpose and is the only type that should be used.
More information can be obtained from your local heating contractor.