Outside Air Source
This air vent may alleviate smoking problems.

If you are having a problem either keeping your fire lit or having smoking problems, installing an outside airsource may be beneficial. Keeping a fire lit takes different factors including air and fuel for burning. The products of combustion include water vapor and carbon monoxide, so being sure that the fireplace will vent properly is very important to the safety of the home as a whole. One way to improve air flow is to install an outside airsource. An outside air source is a vent that provides fresh air to feed the fire.

For years building codes in most parts of the country have required these to be installed during new construction and most homes already  have them.They look like a small rectangle iron grate, and most often located on the back wall of the firebox , these normally slide to the right and left to open or close Their is a verity of styles found  around the country some being round in shape. They to supply air from the outside so as not to rob  air from the living space of the home. My experience is that many don’t open as they have been rusted shut or the homeowner is not familiar with how and when to open or close them. We have all  sealed our homes up as tight as an envelope with air tight windows, doors, weather stripping, and attic insulation and our appliances are air starved.  That is why building codes require outside air to be supplied to all  gas  fire appliance including fireplaces, hot water heaters, and furnace equipment

A fire that burns well will actually increase draft. In order for a chimney to draft properly, there must be a good air flow from the firebox to the top of the chimney. The fire in the firebox warms the flue system so that the products of combustion will flow up and

Fireplace Smoking Problems
Installing a SmokeGuard is simple.

out of the chimney. If the flue system is too cold the outside air coming down the chimney may be heavier than the products of combustion coming up the chimney which can cause a smoking problem. If installing an outside air vent does not solve your problem, a less intrusive repair would be to install a SmokeGuard which makes the size of the firebox smaller so that the products of combustion may be vented more efficiently.

An outside air source can make getting a fire started in your chimney easy even for beginners. With ample outside air and a good set up of kindling and good, seasoned wood, anyone can get a nice fire burning. One thing I will caution you about when it comes to outside air sources is to watch them being painted over. Whether the vent is an outside air source or simply a vent on the front of a wood stove feeding the fire in the stove with air from the room, if you get the area painted be sure that the air vents are not painted or sealed shut. This can cause problems, especially if it is a vent on the front of a wood burning stove that requires the air in order for the wood to fully combust.

Having an outside air source installed is generally not a costly process, but consulting a professional over where to systematically place the vent is recommended. The professional The professional should  discuss with you both indoor and  outdoor variables such as other competing appliances in the home, large hills, trees, or other obstructions that possibly may be a factor for a sluggish draft.

Clay Lamb

Clay Lamb

Clay Lamb is a Cincinnati Chimney Sweep contractor and the executive producer of the YouTube channel, podcast, and blog Ask the Chimney Sweep. He is also an award-winning educator and public speaker in the chimney and fireplace industry.

AsktheChimneySweep.com….Educational Videos

AmChimney.com….American Chimney Cincinnati, OH

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Clay Lamb

8 thoughts on “Outside Air Sources

  1. I just read through this article and was wondering, we have and woodburning stove insert and when we turn on kitchen or bathroom fans they draw the smoke back down the chimney into the house. Would opening this vent help with our problem? We realize our home is pretty air tight and we usually open a window before using the fans but sometimes it’s not enough.

  2. We have big problems with a lot of cold air coming inside the house thru the outside air intake door and the chimney trap door.
    Would it help to put a big piece of non-combustable insulation inside the bottom vent-type doors (under the firebox) where the outside air intake door is ?

  3. I have a masonary fireplace. I have to crack a window to get it to draw well. I raised the fire grate up and installed a smoke deflector and it helped. I want to install a 4 inch pipe in the fire box for air. Will this work ? If so where should I put it in the fire box?

  4. Greg, A big congrats goes out to you on all that you have done. It is obviously a serious negative pressure air in balance in your home. As far as the outside air source I’m somewhat surprised that you don’t already have one of these in your fireplace. May I suggest going to a local brick supplier in your area, or even go online to investigate these vents. Different Mfg. have different requirements for the positioning of their outside air vents. Some are 3′ round, while another manufacturer may produce a vent about the size of one of the firebricks found on the back wall of your fireplace. As far as saying this will solve your problem, would depend on the severity of the negative air pressure issue. I have seen negative air problem resolved by the homeowner simply changing out their expensive furnace air filter to a much cheaper filter, (replace more ofter) that allowed the proper air balancing to be pulled from the room within the home “evenly”. Due to the much thicker “filter mesh media found in the expensive filter, this would not allow air movement from within the cold air room vents and started to down the chimney, located in the basement.

  5. I have a masonry corner fireplace with ash dump in the center of the fire box floor. I would like to raise the floor of the firebox and convert the ash dump as the source of outside air. The dump entry is 7.75×4 inches or 31 sq inches. Will this be large enough? Do I need to push air from the outside into the box to obtain enough air flow? The firebox dimensions are wxhxd 35x23x22
    I plan on installing ceramic glass doors that are “air tight”.

  6. Thanks for all the stats but here’s the problem. I think you obviously agree you have an air balancing problem within the house otherwise you wouldn’t be seeking an outside air source. Most outdoor air sources are too small to start with, but much bigger you’re going to be sitting in the living room with a winter coat. This will definitely be a trial and error. P.S. I’m sorry, I’m laughing here as picture you and your family sitting by the warm fireplace with big winter coats around the fire! Burn safe and warm even if you have to wear your winter coat. Clay

  7. My wood fireplace had been converted to gas DoD it still need this vent open? Also when the fireplace pilot light is out in the winter would cold winter air come in and create moisture inside the walls?

  8. Hi I’m currently on vacation at Disney World with the grandkids, but I would quickly say you should get an inspection with a chimney sweep to real assess the moisture situation. You can use the sweeps finder on http://www.nscg.org Additionally get any manufacturer’s tags on the equipment and contact the manufacturer for their direct advice. Best, Clay Lamb

Leave a Reply

Your email address will not be published. Required fields are marked *