Instant, No-Cost Test of Fireplace Downdraft
I know what you’re thinking, why is this ‘how-to’ article on Medium instead of Youtube? Because for many tasks, watching a video is 100 times slower than a simple text list of steps:
- ON A COLD FIREPLACE OR FIREPLACE INSERT, drape a very thin piece of plastic in front it so that the plastic covers the entire opening.
- If the plastic…
- ……. gets sucked into the fireplace, it’s OK to light the fire.
- ……. blows into your house, don’t light the fire. Smoke would billow into your house if you did.
If you’re in a hurry, you’re done. That’s the whole deal. Have a nice day.
For extra credit tape the piece of plastic to a stick, also called a dowel. Or if you got your plastic from a drycleaner’s plastic bag, perhaps you might straighten out a metal hangar and use that.
When I installed an “insert” (a cast-iron stove sorta thing) into my fireplace, learning to deal with drafts became an absolute necessity. Apparently my old, open fireplace constantly sucked air very forcefully outward, so backdrafts never happened. But the insert apparently changes the physics due to the cross-sections of the vent and door, or maybe the fact that the fireplace now has a sealed door on it, so the chimney (and now its metal flue) stay much colder overnight. Lighting a fire in the insert, when there was a draft, caused smoke to just pour right out of its air intake like a river filling the room. The use of the term ‘draft’ makes it seem like wind is involved but I don’t think that’s often the case. I’m pretty sure it’s the pressure difference between the room and the chimney… negative pressure, meaning air is sucked into the room.
Anyway, I tried different methods to reliably detect/measure the draft:
I thought that my $30 infrared(?) gun-style thermometer was gonna be the methodical answer: pointing it inside the insert clearly showed lower temperatures than the room. But it was hard to be sure what temperature difference was troublesome.
Then I just tried holding up a lighter to the partially opened door, seeing which way the wind blows. And it seemed reliable, but again not too clear how much was too much. Then the plastic idea hit me. I think this is it. You can find the video on Youtube.
