Wipe down the Comfort-Aire furnace's ventilation grills, found on the sides of the appliance, if you find the heater's output decreasing. Use a damp rag and wipe thoroughly to remove dirt, grime and dust that can get trapped as the device blows out air. These may be blocking one or more of the vents, limiting the heated air output. Use caution if wiping a running furnace, as the surface areas may be warm or hot to the touch.
Check that the furnace is plugged directly into a reliable power source and not an extension cord if you notice low heating performance or if the furnace shuts down unexpectedly. Overloading an outlet with additional high-powered devices is also discouraged, as the furnace needs full power to run well.
Inspect the furnace's rubber hosing if your Comfort-Aire model uses a separate boiler to connect to the heating box. A cracked or broken tube can cause a severe loss in heat and poor performance. Replace any hosing as needed, referring to your specific model's user manual to find the appropriate part numbers.
Check that the intake area is free from cold drafts, as this forces the furnace to work harder. Most Comfort-Aire furnace systems draw air in from an intake valve, which should be oriented toward a shielded area rather than an area near a door, window or poorly insulated wall.
Clean the intake valve if you notice loud humming or noises from the furnace. This may indicate that the valve has become clogged, causing the internal mechanisms to spin on a lower volume of air, which can increase stress to the system. Use a damp rag and wipe clean, being careful not to push any debris deeper into the valve.