What kind of increase does over fire air create?

[Springfield Acer]

I'm looking at a used evaporator and it makes the published GPH with natural draft and I think it is the right size for me but, I want more that the published natural draft rate. I currently have forced air on a 30% smaller pan and get almost the same GPH as this larger pan. Is there a rule of thumb percenatge of gain one can reasonably assume when adding forced air?

[Gary R]

This thread has the link to UVM's info.

http://mapletrader.com/community/showthread.php?7273-Adding-air-over-fire-to-your-arch

I don't think the smaller arches will get as great of an increase.

[maple flats]

I gained about 30-35% faster boil using 1/3 less wood with air over fire. I've heard the figure of 15% more with air under fire but I'm not sure. If going air over fire it must be high pressure air, a high volume squirrel cage blower will not do it. The benefit come from the top air being able to blow down at the fire and create turbulence. The mixing of the air and gases is what does it.

[Gary R]

Springfield Acer, thanks for the beer last night. It was fun to talk maple for a couple of hours. Keep us updated on what your going to buy or build!

[Springfield Acer]

Thanks Maple Flats. I'm all for the over fire air as I use it now in my backyard set up which comes from a two cycle leaf blower on idle. My cement block arch literally roars. Now that I am considering an upgrade I'm looking for that % increase because the stats on the one I'm looking at do not reflect any forced air. I was guessing 30%. Thanks for the confirmation.