THIS is Why Your Fireplace is Smoking

Home Fireplaces Basement Fireplaces THIS is Why Your Fireplace is Smoking

We get hundreds of calls about smoke smells in homes coming from a fireplace. Sometimes it’s in the room where the fireplace is, sometimes the basement, sometimes the floor above… There are lots of reasons that this is happening:

Least Likely Reasons But Should be Checked

  • There may be a blockage like an animal or a nest or a lot of buildup in the chimney.
  • There may be a problem with the chimney damper.
  • The chimney may be damaged on the inside.

These are all concerns and all things that should be checked, but these are NOT the main reasons for a smoky smell from the fireplace and only make up about 20% of the reasons why this might be happening.

The NUMBER ONE reason for smoke smell has to do with the physics of air pressure. 

The first thing to know is that fire requires oxygen as fuel. Unless a fireplace has a dedicated fresh air intake (these have only started to be installed in the last 20 years), the fire is drawing A LOT of air from the house, heating it up and blowing most of it up the chimney. Just like if you were to put a really big fan in the window blowing air out of the house. This creates a lower air pressure in the house than the pressure outside.

The next thing to be aware of is that there are other appliances that do the same thing. They blow air out of the house. Your water heater, furnace, dryer and kitchen exhaust fans all do this. Have you ever sat in a restaurant near the door and have a cold wind rush in on you every time the door is opened? That’s because restaurants have large exhaust fans that draw air out and there’s nowhere for air to come back in. Except for the door. Where your table is.

The next thing to know is that cold air pushes downward and heat pushes upward. We all know this. Think hot air balloons.

Knowing all these things, now let’s look at the 3 main problems that might be happening:

  1. It is cold and drafty near the fireplace.
  2. No matter what you do, all the smoke comes in when you are trying to start the fire. And if you have the determination, you light it anyway and it takes a few minutes for the smoke to start going up the chimney.
  3. The fire is going great. You’ve just sat down to enjoy a book and after about a half hour or an hour, smoke starts pouring in.

So… Pressure. In this day and age of efficient homes, we have high efficiency appliances, super duper insulation, double-glazed and super-airtight windows, etc. Homes are airtight and appliances push out the air. Most furnace and HVAC  (heating, ventilation and air conditioning) specialists don’t think of the home as a pressure system.

Here are the REASONS why these problems happen:

  1. If it’s cold and drafty near the fireplace there are 2 reasons/solutions. Note that this problem is most apparent with basement fireplaces:
    a) The damper may not be sitting properly or may have gaps in the frame. You can take some tin foil and push it into any little holes/openings in the damper frame or you could consider a new damper such as a lock-top damper which is more airtight. We can advise you on this.
    b) There is not enough fresh air or a very low pressure in the area of the fireplace. This is a common problem with basement fireplaces. Consider installing a fresh air intake into your furnace room. Most HVAC companies can do this and it involves drilling a 4 inch hole in the wall of the furnace room to the outside and inserting a PVC pipe with elbows on each end pointing downward. The more expensive solution is installing an air exchanger or HRV (heat recovery ventilation) unit. The least expensive is to open a window in the furnace room a bit.
  2. Smoke coming in when the damper is open and you are trying to light a fire is solved by equalizing the pressure in the room where the fireplace is (again, usually this is the basement). Simple way – open the window and leave it open for five minutes before lighting the fire. Then… “Prime” the flue. This means you have to send a lot of heat up the chimney to reverse the draft and get it going upward. Take a few sheets of newspaper and roll it up like a torch; light the end and hold it up at the top of the fireplace near the damper or even so the flames are touching or licking the the open damper. Keep doing this for a couple of minutes until that draft is sucking the smoke out. Then light your fire. Then, gradually, begin closing the window bit by bit.
  3. Smoke starting to come in after the fire has been going a while means that, because the fire itself is drawing air out of the house, it runs out of make-up air (the heat doesn’t have enough “umph” to push the smoke out of the chimney). Solution: open the window in the room until it stops smoking and then gradually close it, but leave it open an inch or so.

Fireplace: Due Diligence

So there you go. If you have ANY questions, just give us a call and we can diagnose and help you sort it out. As a disclaimer, you should always, always, always have a professional check and clean your fireplace if you have been using it or if you don’t know the history of it. You should also always have a set of fireplace tools, fire extinguisher and a metal bucket near the fireplace so that you can manage any mishaps.

When I get a little more time, I’ll make a video about the proper way to get your wood fireplace started. Stay tuned!

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