Cleaning ideas for 6" Dia. Combustion Air Ducts

I am not a ME so there is much of which I am ignorant in this area. I need some solutions for my home’s combustion air ducts and how to clean them. The central unit ducts/plenums were recently cleaned but their system and equipment didn’t lend itself to cleaning the combustion air ducts. Have any of you done this or have ideas?

There is one 90 degree elbow in each 6" Dia. duct. The duct for the gas hot water heater is about 2’ off the cement. The furnace duct is much higher so snaking something through it would be easy.

Those ducts were not filtered so I put a coarse filter on the inlets outside and finer filters on the outlets in the basement. I had to cut those from a pre-made filter. Those have helped tremendously. However, I would like to clean those prior to winter, if possible.

Thank you in advance for your ideas.

There are combustion air ducts, which bring fresh air in for the combustion process. They are generally fairly clean since the are only handling fresh air from outside; maybe fairly dusty if you live in a dusty environment. They should have a ¼” mesh or window screen mesh at the bldg. entrance to keep bugs, etc. out. They should terminate near the heating units, in the Mech. Rm., in a vert. run down to be near the floor, or right into the heating unit, with an open end. Terminating them down into a five gal. bucket, 2/3rds the depth of the bucket tends to reduce the cold air movement into the bldg. unless the furnace is running.

There are exhaust ducts and chimneys which take the combustion products out of the bldg., usually without any mech. power assist, just properly sized and heat rising to exit the bldg. If the water heater and the furnace are gas fired, the flues should be fairly clean, if the burners are properly adjusted. Fuel oil is a little less clean burning, and coal and wood produce the most flue residue. Wood can cause creosote, which clings to the chimney liner and can cause chimney fires. You can see all this stuff, and the need for cleaning, if you look down the chimney with a flash light.

They make round (ball or cylindrical) wire brushes for cleaning the flues. A rope (or rod) on each end, and you just pull them back-n-forth as you progress through the flue. Or, tie the brush to the rope at the bottom of the chimney and pull it up and drop it down in the chimney. It is really messy work, and you would like some forced air from a window fan (or several fans), or some such, blowing into the house (pressurizing the house) so this air exhausts out of the house through the flues you are working on. It is best if you can take the flues apart at the elbows, cleaning them by hand, and otherwise be working on straight runs of duck work. There shouldn’t be a filter in the exhaust flues. It might get plugged and cause carbon monoxide problems in the bldg. There might (by code) need to be a spark arresting screen (and squirrel stop) on the top of the chimney.

dhengr, I am wondering how the bucket helps in any way.

Lacajun, chimney and duct cleaning brushes products are readily available at most hardware stores. There are also companies that specialize in this service everywhere.

For 90 degree elbows it is usually easier to pull the brush through rather than push with a rod or something like a sewer snake. You can get a pull cord through with a vacuum cleaner and a wad of newspaper.

The bucket calms/stills the air movement around the open end of the duct, sorta trapping the colder air movement. Otherwise, the cold air from outside tends to settle to the floor, and spread out, and draw in (allows in) more cold air. These combustion air ducts are often larger than needs-be, because the Mech. guy happens to have that size duct for other things too. You can often see the air flow with smoke or some such. That’s why all construction guys used to smoke. :blush: Most older houses have enough natural air leakage so it is doubtful that combustion air ducting is needed. The ultimate of course, in cost and mech. complexity, is the newer, powered heat exchanger fresh air system. A problem which can occur is the use of too powerful exhaust fans in the kitchen or bathrooms. These can tend to reduce the natural chimney flow at the heating units, or even draw the CO inward. Thus, the need for CO detectors, particularly on newer tighter construction which sometimes actually happens.

The first chimney cleaning I did was back in the early 50’s, on five wood burning cabins. We used a 3” dia. oak log, 18” long, with burlap rags tacked onto it. Just dragged it up and dropped it down the chimneys 8 or 10 times, and then cleaned them out at the floor clean-out doors. My old man made me do it, because when I was all done, I could just go take a swim and clean up. He also told me the dirty chimney were my fault anyway, since it was also my job to cut the firewood and keep it stocked at each cabin.

That is what I thought you were suggesting. Problem is that it will not work. There is heavy cold air in the duct which will fall into the bucket and overflow it onto the floor. It is like putting an inverted bucket over a chimney, The smoke will fill the bucket and overflow around it.

I’ve not found a company that will clean those air ducts. I just paid a company to clean the rest of the system so this is something I think I can do.

The ducts are super dirty because they’ve never been cleaned. We’ve had a lot of particulate, dust and ash, and smoke in the air. I recently learned that I have mold spores on that side of the house that are the same molds found in the house and basement. The mold levels in the house are within normal range. My genes may be unable to handle them. Those are being analyzed now.

Putting filters on the inlets and outlets has greatly reduced the dust in the house. Dusting is not something I enjoy but have to do because of allergies. Anything I can do to get more miles from my dusting efforts will be good for me.

Thank you for the ideas.

Something here + a shop-vac with a HEPA filter shoud do the job.

Thanks, MintJulep. I looked at those over the weekend. They seems to do a really good job on vents and that’s probably the way I’ll go.