Dumb question, probably, but you guys have come through for us in the past...

Our house has a fireplace installed by the previous owner with two sliding knobs. Our question is, what are these?


The top slider is probably the flue. If so, is convention that the in position is opening or closing the air to the chimney?

The center knob is obviously for opening the door.

Finally, what do you think the bottom right slide does? If you had to guess, what is the difference between the "in" position" and the "out" position? We've played with it when the fire is working but we don't notice a difference.

There is some kind of electrical blower on the bottom which, when you plug it in, forces air out the vents on the bottom. However, it doesn't seem like this slider on the lower right controls the air coming out of those vents, at least not obviously.

Any ideas from the world of Stack Exchange?

  • 2
    I'll defer to the experts but my guess is that it's either fresh air intake or damper control.
    – Mike B
    Nov 29, 2010 at 6:57
  • 10
    I first read this as "Who is this knob in our fireplace?" and thought "Santa".
    – Jay Bazuzi
    Nov 29, 2010 at 14:50
  • Hilarious, Bazuzi! Nov 30, 2010 at 23:09
  • Your photo is gone. Please upload it to the site, so it can stay around as long as the question.
    – Tester101
    Feb 24, 2015 at 14:06

4 Answers 4


The upper knob is logically the flue control. You really don't want to close off the flue with a roaring fire going. The exhaust gasses need to go somewhere. If not up the flue, then...

The lower knob is logically air intake. It might be from inside the house, or if the insert is externally vented (best) then the air for the fire comes from outside. In either case, shutting that down will dampen the fire, but it will do so gradually as the oxygen in the cavity is depleted. And I don't know if it is designed to completely shut down the incoming air at all.

Personally, if I were the previous owner who installed it, I would have kept the instructions for the insert around. And then when I sold the house, I would have passed on (to the new owner) a whole pile of instruction manuals for every item in the home. Read the manual.

  • 3
    "If not up the flue, then..." Too often on the internet someone assumes I know what they mean and so they just write '...' and then I am confused. So: "If not up the flue, then in to your house, which is really bad for you."
    – Jay Bazuzi
    Nov 29, 2010 at 12:17
  • Haha, that happened to my old roommate when he moved into his new apartment. I showed up for his house warming party, and the entire apartment was filled with smoke! Of course, we never let him live it down.
    – Doresoom
    Nov 29, 2010 at 15:05
  • 1
    I recall the time when I was starting a fire in the fireplace. Not much of a draft at first. But worse, my wife had just started making dinner. So, she turned on the exhaust fan over the stove. To our alarm, we suddenly had a stream of smoke coming into the house, no longer going up the flue.
    – user558
    Dec 2, 2010 at 11:26

Manufactured fireplaces generally have air intakes in the lower front corners of the firebox. These are air intakes that you can open or close to adjust the fire and sometimes deal with a finicky fire that lets smoke into the house. When a fire is completely out, you can close these intakes just as you would your damper. If you go up into your attic, you can usually see these running up the chase and out of the house. They may vent through the roof, the eves/soffit, or the wall. Failure to close these vents can admit wasps and bees into the home in the summer. I recommend placing wire mesh at these openings unless you want to chase wasps for five years like I did before I figured it out.


Is that a wood burning fireplace by any chance? (These days you can't tell from a picture!)

I've seen a lot of fireplaces that have a trap door in the bottom for cleaning out the ashes. You open the trap door and sweep down the ashes. The ashes pile up in a designated bin in the basement, forever, until you sell your house.

My crazy, outlandish theory is that you use the lower knob to open a trap door on the bottom, then turn on the fan to blow the ashes down into the basement. Hey, it's just a theory :)


When you switch the lever to the left,it diverts some of the blower air back to the vent right under fire to keep it well oxygenated

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