Question for burn engineers?

[jkupcha]

My zero clearance fireplace is EPA exempt because it has a air/fuel ratio above 35:1. I was wondering what the result would be if I closed off some of the external air vents that are fixed open to gain this exemption. I am thinking that would give me almost 100% control of the combustion air by using the vent lever.
The fixed open vents are easily reachable just above the removable metal heat exchanger plate at the top of the firebox. A steel plate could easily just rest there and block the air. One vent on each side. I guess I could experiment by trying one side then the other.

But just wondering theoretically if combustion air would be pulled stronger into the controlable vent as hot air rises up the chimney and new air gets sucked into the unit?

 

[Fsappo]

I'm not an engineer by any stretch, but I have been in the wood burning business for a couple of decades. So, you have a chimney that has an updraft. It wasnt to pull X amount of CFMs up the chimney. It gets the air from 3 holes. You close one hole and assuming the CFM of air moving up the chimney remain the same, the velocity of the air in the remaining two holes would increase to compensate.

Science aside, it just doesnt seem to work out that way from "MY" experience. If I have an air control open on a wood stove and I close it halfway, less air goes into the fire. It's not the same amount of air, moving faster thru a smaller hole. Now, on a fireplace (I'm assuming it has reasonably tight glass doors on it) I would expect that if you close one of the air intakes, you would end up with a slower burning and dirtier fire. I'm also assuming your fireplace is simply baffled where the smoke goes out, with no provision for secondary combustion by means of air introduced via air tubes.

You would probably burn less wood, burn dirtier but not hold more heat inside the fireplace.

So from my experience and in my opinion, you would be gaining little. But again..I'm one of those guys who kind of glide thru the wood burning industry without getting too caught up in the science of it.

 

[jkupcha]

Franks,
Thanks, great thoughts and probably very accurate. My wife had an easier idea. The fixed air intake is a vent a few feet up the external chase. She suggested just testing by putting a piece of cardboard over the vent for a few minutes to see how the firebox performs. That way I can easily reverse it without making mods to the stove. I'll report back.

 

[Fsappo]

Yeah, let me know. I guess it's never too late to increase my smarts a little!