Over-Draft?

[BruceNorEast]

Over the past year I lurked this site, and one item that seemed a no-brainer was that I'd need a damper for my 33 foot chimney.

So when we bought our stove, I had to argue with the salesman, his manager and then the installers - they all told me "that stove is tight, you don't want a damper!" I bought one anyway, and we all came to the agreement that I'd install it myself later if needed.

I've had several small fires, and then a larger one and all seemed fine. The larger fire I kind of snuck up on - letting it grow in intensity slowly and damping it down once the secondaries were running well.

Last night I lit a hot fire, cranked it up and let it rip through the kindling and the next load. When I was ready for bed I loaded it up full and figured I'd back it off until the secondaries were dancing and hit the sack.

It took two hours for the intensity to die down, the draft was really roaring and the outside temp wasn't all that low (in the 40s).

This morning I did the dollar bill test: On the door it was fine. On the ash door there were places where it was not very tight, but I really don't think this had anything to do with the intensity last night; because the ash grate is always closed (per the manual) there's very little air coming in that way (checked this several times, no difference observed when the ash door was open versus closed. There is a huge difference when the grate is open!).

So I figure this weekend, I'll be installing the stove pipe damper, do you agree?

I only ask because of what the salesman, his manager and the installers all said, and that I recently read here that some people with long chimneys have put metal tape partially over their air-intake to deal with this.

 

[HotCoals]

What is happening is because of the intake air that can't shut down to where it may need to be you're getting to much air.
Now the damper mat help. I still have my damper ,I could not get myself to take it out with the new stove 4 years ago. But since mine is a cat stove the idle air hole is most likely way smaller then yours. You may have more then one hole also. Now you could partly cover those holes with magnets or tinfoil or whatever but I'm not going to tell you to do that. Since you have a insert it probably would not be practical to do that. Your draft is only going to get stronger has it gets colder out.

 

[begreen]

The salesperson is full of it. Modern stoves are not air tight. The secondary supply on this stove is wide open and the primary does not close tight. Put in the damper.

You'll have to experiment a bit with its operation. In cold weather you may be able to keep it partially or mostly closed all the time, but maybe not. In milder weather you probably will need to always open the damper a few seconds before opening the stove door.

Be sure to install it a few inches into the pipe so that when the damper flap swings it doesn't hit any of the screws securing the pipe sections together.

 

[firefighterjake]

"Really roaring" = what temp? I only ask because I can have my air open all the way and there are a lot of flames, but not so much heat . . . and even with the air backed down and the secondaries going it can be hard to tell what is hot and good and what is too hot.

 

[BruceNorEast]

Thanks Guys!

HotCoals: "you're getting to much air..." I think you're right. FYI, the stove is a stand-alone sitting in front of the fireplace (a little uncomfortable working behind it, but doable). I'll check out the intake holes and see if I can try your magnets and tinfoil idea.

BeGreen: "The salesperson is full of it. Modern stoves are not air tight. The secondary supply on this stove is wide open and the primary does not close tight. Put in the damper." It sure looked like the secondary supply was wide open - as though there was a row of blow torches at the top pointing at the window
I'll take your advise and add the damper, even if partially blocking the air intake works fine; the stoves owners manual mentions an external damper - that if present, it should be closed in the event of a chimney fire

FireFighterJake: ""Really roaring" = what temp? ..." The manual says that opening the air control (which "fully uncovers the primary air shutter") results in a high burn rate, and temps of 350 F to 400 F. The stove top thermometer, placed in the center of the center stone on the stove top, read around 370 F. But it was roaring as far as action/speed and sound. The secondary flames didn't do their ghostly dance (except for areas near the back corners, behind the wood) but rather were raging, blasting over the top of the wood pile from the rearward secondary air tubes, and the front ones were blasting toward the window and up and out the top to the chimney. I turned the air vent fully off and waited for the flames to die down - took about two hours, and the wood seemed to have converted mostly to charcoal. While the coals ran most of the night, the full load was consumed in less than three hours, with the inlet air nearly off!

 

[begreen]

If the secondary combustion is robust, don't be afraid to close the air control all the way once the fire is burning well. It doesn't close off completely.