You depend upon your furnace to keep you warm all winter, so it can be alarming if it starts making loud noises. Knowing what causes them so know when it's time to schedule a repair is vital. The following guide can help you determine the cause of the furnace noise.
Issue: Start Up Bangs
In most cases, the initial bang you here each time your furnace pops on is nothing to be concerned about. The most likely culprit is the hot air causing the air ducts to flex and pop when the temperature inside them rapidly changes. If it's an exceptionally large bang, then the main duct by the furnace may be the one most affected, possibly flexing more than it should due to a weak joint or panel. Check it over for loose or missing screws and replace as necessary.
This noise can be a concern if it is coming from the furnace itself, especially if you notice that the furnace shakes or vibrates when the bang occurs. A malfunctioning ignition and fuel pan means that too much fuel is being delivered at startup, leading to a small explosion when the furnace ignites the fuel to cycle on. This can be a major fire hazard, so you need to turn off the furnace until you can have it repaired.
Issue: Whistling When Operating
A whistling noise typically has one of two causes. The most likely cause of the problem is if the filter either needs replaced or it wasn't fit into its housing properly. If it has been more than two months since the last replacement, change it out to see if that takes care of the problem. If you have recently changed the filter, make sure it is resting in place properly.
The other cause is that the furnace air is whistling in the ducts. Gaps in a duct where it has worked loose is a likely culprit if the noise just started up. If you can see your ducts, such as in an unfinished basement, you can look for loose ducts and repair them. Otherwise, you need an HVAC tech to inspect the ducts. If the noise has been going on for a long time, then the problem could be your duct system is sized too small for your furnace. The whistling is the result of too much air mass being forced through narrow ductwork.
For more help, contact one of the heating repair services in your area or visit a site like http://www.coeheatcool.com.