Forced air questions

[drewlamb]

Considering changes to my evaporator for next year, and I've got a couple questions about forced air. Can an air blower system - above and/or below fire - be installed on an arch whose arch doors and bottom are not airtight? Everything I read talks about it being air tight but I can't figure out why this is so important beyond perhaps blowing ash out of the arch. Seems if that's the only issue that I could guard against that with insulation. Besides the extra cost, I'm reluctant to completely rebuild my arch for forced air when I'm not really sure the traditionalist in me will much like the electricity necessary to run it or the noise it'll make. Still, if the performance is much better, that might make it worth it for me. And what kind of enhancement could I expect on a 3x8?

[Cuseman1000]

My arch is not air tight. It will push sparks and flame out of the door gaps, and where there's no pan gasket. Even without being air tight it still makes a huge difference in boiling rate.

[RileySugarbush]

Just adding a little under fire air through the grates should make a big difference in your production rate. If your arch is a little leaky right now, that means the draft suction of your stack is also drawing in air through the leaks, not through your draft door. Less air for initial combustion. Adding a relatively small blower under the grates will drive some oxygen through your fire. Put an inlet damper on the blower so you can run it up to the point you have ashes blowing out the door and lower it a little bit.

For the last several years I was running a 200 CFM low pressure blower on my 2x6. I could run it wide open without too much ash blowing out. Now with my added over fire air I need an airtight door and good gaskets. Others have used more. For your rig a 300 to 400 CFM blower would really help. Much more than that and you may need a lot more wood.

[Russell Lampron]

I never thought that I needed a blower on my 2x6. With the 17' stack I thought that the natural draft was good enough. I added a blower a couple of years ago and what a difference it made. I only have it blowing under the grates and it doesn't have an air tight front yet. I have it damped down so that I can still fire the evaporator without turning the blower off. I don't loose the boil or gradient when I fire anymore and I can burn what ever size wood that I want. I have burned chunks that would barely fit through the doors and still had a good hot fire.

[drewlamb]

Great info - thanks guys. Do you have to adjust the flow much once you're up and running? My rig sits over a recessed pit that draws air in from the front, under the ash clean out/damper door. Most traditional rigs around here I've seen are set up this way, with the ash door removed and extra air coming in underneath from the pit. I assume I'll have to reattach the ash door and fill in the pit...

[maple flats]

i have over and under high pressure air and I do not have an air tight front. I get no smoke or sparks out the front and I do not need to slow or stop the blower to fuel. I just open the door and the draft pulls everything inward. I thought it would be pushing out. Realize this is high pressure not high volume air. It may be different with a squirrel cage blower.

[vernon]

I am wondering if I can place my blower outside of sugar shack and pipe the air to arch, to reduce the noise. I am building a new shack and can put air duck under concret floor very easy. Has anyone tried this and does it reduce the noise? This is my first post and not sure if I am the right place to ask the question? Vernon

[boondocker]

when i get my new beast, i am considering a blower system but im not sure how the over / under deal works. does the blower blow the air back towards the door from the back of the arch for over air??? i assume the under air is being blown up thru the grates, correct. excuse my blower ignorance:)

[WESTVIRGINIAMAPLER]

Vernon,

I have a 1hp high pressure blower that supplies under and over air for my arch and it is outside and air is piped to evaporator with 6" PVC and it took about 36' with 3 elbows and it works great and don't see where the elbows hurt anything.

Here's the link for the pictures of the pipe.

http://s203.photobucket.com/albums/aa160/wvmapler/Air%20Injection/?action=view&current=IMG_3137.jpg

[RileySugarbush]

when i get my new beast, i am considering a blower system but im not sure how the over / under deal works. does the blower blow the air back towards the door from the back of the arch for over air??? i assume the under air is being blown up thru the grates, correct. excuse my blower ignorance:)

The under fire air is simply up through the grates. Mine is a 200 CFM low pressure blower and no real restrictions in the angle iron grates. Others use nozzles in refractory grates which may require a higher pressure blower.


The over fire air is typically a higher pressure blower through small nozzles arranged around the top of the firebox and shooting high velocity air over and slightly down into the top of the fire. The idea is to introduce oxygen up there with a lot of turbulence to make sure it mixes in with the unburned gasses above the fuel.

High pressure in these cases is a relative term. My under fire air will stop flowing anything with 0.5 in H20 back pressure My overfire air is a half hp motor and can flow 100 CFM with a 3.5" H2O back pressure from the nozzles.

Note that 3.5in of H20 is equal to about 0.125 psi, which isn't really a very high pressure, but is for a blower.

[Russell Lampron]

Drewlamb once I got my damper adjusted the way that I wanted it I haven't had to change it at all. That was 3 seasons ago. I have my ash door/draft door on and have covered the area under the arch with fire brick so that the only air that gets in goes through the blower.

[RickinFarmington]

I just bought a 2x4 Mason raised flue evaporator and want to add forced air.
Several questions: After sealing my ash door, can I simply add a 6 inch round inlet on the back of the arch below the grates. This would have the effect of pressurizing the area below the grates and blow air up though the entire grate area , I think.
Is a round inlet ok or would it be wise to use something that would cover the entire width of the input similar to a standard smoke stack coming out of the top of the arch.

Rick

[RileySugarbush]

Round is fine. If you find that there is one area in your grates that gets more air you can place a firebrick in their to distribute the air around a bit.

[RickinFarmington]

Thanks for the input.

[Brad W Wi]

I'm wondering about stack size. I have a 2x8 with a 10" stack. Would this be large enough to handle a blower?

[mapleack]

I'm wondering about stack size. I have a 2x8 with a 10" stack. Would this be large enough to handle a blower?

Yes, our 3x10 has a 10" stack and boiled great with forced draft wood.

[Flat Lander Sugaring]

I am wondering if I can place my blower outside of sugar shack and pipe the air to arch, to reduce the noise. I am building a new shack and can put air duck under concret floor very easy. Has anyone tried this and does it reduce the noise? This is my first post and not sure if I am the right place to ask the question? Vernon

Most definately you can install blowers outside. Until this year before AOF both blowers were outside. Everything will be outside this year and hoping 15' away from sugar house.

[RileySugarbush]

Most definately you can install blowers outside. Until this year before AOF both blowers were outside. Everything will be outside this year and hoping 15' away from sugar house.

Sure you can. If you are using a low pressure blower then make sure you use very large ducts.

[Paddymountain]

I'm running two 110 cfm fans on my 30x8' arch. I have 2x4 box beams coming in from behind the firebox just above the grates, with 3/8" holes spaced 4"
apart. I have airtight doors that I built, and I don't turn the fans off to refuel the arch. I think it works really well,but I have not personally seen anyone elses setup so I have nothing to compare it to. There are some pictures in my photobucket that show the fans and box beam.

[Flat Lander Sugaring]

So each fan does AOF on its side that it is mounted too?
Do you ave AUF also?
just a little confused,I know there isn't much help for me:D

[Brad W Wi]

Paddymountain I sent you an P.M. Thank you.

[Paddymountain]

No, the fans discharge air right above the grates. The ash door is open about 1" as the latch is not there,but it doesen't seem to matter.