Musty Smelling Furnace Problem and Solution

You are experiencing a musty or dirty smell from your furnace when you turn it on. You get this each year and may be experiencing asthma or breathing difficulties including sinus problems and these go away or reduce when you leave the home.

Most Common Answer:

Is the filter dirty? When the filter gets dirty the air is blocked by the debris buildup. This causes the air to be sucked into tighter and tighter spaces. This reduces the air your system can heat and reduces the efficiency of your furnace, but more so than this it causes the velocity across those open parts of your filter to speed up. This increase in speed allows debris to be pulled through the filter and be deposited on and in the blower motor, the blower wheel, the heat exchanger and, if you have air conditioning, the evaporator coil.

The smell is usually caused by the debris burning on the firebox. The debris you find on your filter, in your blower motor and on the firebox typically consists of the following:

  • Dead human skin (all of us shed skin year round)
  • Hair
  • Carpet fibers
  • Pet dander
  • Pollens
  • Cooking smoke/greases
  • Dust

Putting all the stuff together and cooking over the top of natural gas flames tends to make a smelly situation. This is the most common smell complaint that we receive.

Will duct cleaning solve this smell problem?

No, it will not. Duct cleaning is largely a farce. Keep your furnace maintained and clean with a quality filtration setup and you will never need duct cleaning. The smell isn’t coming from your ducts. It is coming from your furnace heat exchanger. This means a thorough furnace cleaning. It may also lead to a duct cleaning or duct repair.
You should never, ever have a carpet cleaning company clean your furnace. Cleaning a furnace involves taking it apart, taking the blower motor out and removing the blower wheel, removing the burners, cleaning reassembling and then adjusting the air fuel mixture. These pseudo duct cleaning companies are nowhere near qualified to perform these actions.

Second Most Common Answer:

Your ducts are sucking in contaminated air or making your home suck in contaminated air.
If your ducts are broken under your home or in your attic they can act like an aspirator. The high speed air travel through the duct can actually suck in the air from your attic or under your home every time the blower motor is turned on in your furnace. Think of the commercial for Miracle-Gro lawn food. The plastic cup contains a static liquid. The hose attachment is fast moving water going over an orifice or opening to that static liquid. The faster moving water creates suction and pulls out the static liquid. That is an aspirator. Broken ducting can do the same thing and pressurize your home with dirty unfiltered air.

If your ducts are broken they can also depressurize your home. If you have broken ducting in your attic or under your home the air escaping beyond you insulated heating envelope creates a vacuum in your home. A vacuum must be satisfied. This means to make up for the pressure difference between the inside of you home to the outdoors your home will suck in dirty contaminated air from every crack, crevice, plumbing penetration, electrical penetration and even right through the drywall. The average home that is 10 or more years old here in Southern California is leaking more than 15% of its air in the ducting system. Most furnaces in heat mode are moving around 900 cubic feet of air minute. This means that your home is likely sucking in about 135 cubic feet of unfiltered cold dirty air from outside your home.

Forget About Cleaning Your Ducts Cleaned.

Have them inspected and tested for leaks. We perform State Certified Duct Testing. Give us a call and we can help.

If you are having significant allergy problems when the furnace is running you can read a little more about it here.