How should 500 cfm's of air "feel?"

[heus]

Kind of a dumb question, but..
I made a forced air unit from a 500 cfm inline duct booster fan, through about 4 feet of 6" duct, and enter the rear of the evaporator with a 2 1/2 by 12 inch opening. When turned on, I expected to feel a blast of air, but it seems to be just a gentle flow of air. How much air should these things blast into the evaporator? I know that cfm represents volume not pressure, right?

[S Culver]

Is this from lowes or hd sort of thing? and is it the 6" one in a round duct? If so the 6" round ducts residentialy for a house system I think are really good for 125 cfm of fairly low pressure.

[heus]

Its an 8" says 500 cfm on the box, yes its from Lowes

[Bucket Head]

Yes, cfm is cubic feet per minute. Its a measure of volume, both water and air. No idea how much pressure your blower is, but it might still work great even though you don't "feel" much from it. It really does'nt take a lot of forced draft (volume) to wake up your fire. I have a furnace blower (which is way too big but it was cheap) and I restricted the inlets on it to move just enough air to get the fire really working. Taking an educated guess at it, I'm only putting around 25% of the blowers potential output in under my grate. And I too thought it was'nt going to be enough when I first turned it on to see what was coming out of it.

Steve

[Bucket Head]

I should have added that I have no idea what the cfm of my blower is so we can't compare them unfortunately. What I'm saying is you might be pleasantly surprised by the fire after putting your blower to it. Many guys on here were very happy with the performance of their rigs after they installed some fairly small air sources.

We are talking about under-grate air, right? If not, disregard everything above, return the Lowes blower, and we'll start over, lol.

Steve

[TRAILGUY]

tried one last year did not work at all. Hair drier and tape the cool button down my electrician buddy tested draws less then 90 warts and no power to heat element it pushes all the air my stack could handle. short money. made a t out of 1 1/2 pipe and dilled 1/4 inch holds and blocked the ends.

[wiam]

I tried a 6" inline duct booster on my 2x6 last year and was not much use.:rolleyes: Then I stole the blower out of my miller mobile home furnace in my shop and that worked really well.

Will

[maple flats]

From the days when I was in the furnace business, those blowers are rated with no duct. As soon as you have any length of duct the numbers drop. What you did will help some, but not a whole lot. Just remember, you don't have much invested in it but it will help. If you really want impressive results in boil rate AND fuel efficiency, try the over fire combustion air thread some day.

[maple flats]

Anyone wanting a blower for high volume air, I have one for sale. It was rated as being for 2x6-3x10 when I bought it from Bascom's a few years ago. I used it until I went to high pressure over fire air. The blower has a 120v motor and is a squirrel cage ype. The cage is about 12" diameter and I think the outlet air duct was about 6x10". On my 2x6 an 3x8 I had to use a slide gate on the inlet to slow the air some. I'll sell it for $60. You pay shipping or I can take it to Verona Jan 7-8 to save frt.

[Monster Maples]

Heus, There is a place in Euclid called HGR that is an industrial surplus outlet. Check them out, they are in the old Ford plant. I got 2 Dayton squirrel cage fans for $19 that were like brand new. PM me if you need some contact info for the place. If you are interested and want to go there and never been there, be prepared. Don't make plans for that day, don't take the wife, and grab the plastic card.

[heus]

I am going to hope that since I bought the 500 cfm over the 250 cfm 6" fan that it will be good enough. If not, it was only 30.00 anyways.

[Brent]

Here's something to think about.
That rig will boil pretty well with the draft door open and letting in only the natural draft.

The fire box in the arch is less than 2' x 2' x 2' ( the sides slope inward to the bottom.)
Say 2x2x2=8 minus something for the slopes ... say 5 cu ft.

If you delivery 500 cfm to a firebox that is about 5 cu ft
you're going to blow out all the air in less than a second.
That will be tons more air than it takes to make it work quite well by natural draft.

Whether your blower will really deliver 500 cfm into the fire box is another question, but I think 500 cfm in that rig is huge overkill. I'm guessing you'll have stack temps way up there, maybe 1500 degrees and a huge part of your wood will go up there without doing much good.

[S Culver]

Brent your thought is right on track. I have the same problem with customers who get talked into 1200 cfm range hoods. All that air has to come from somewhere! They don't like the smell of fish but they also don't like the smell of the air getting back drafted down the chimney.:o

[heus]

I put a damper in the duct to slow down the amount of air if needed. I really dont think this thing moves 500 cfm, so I'm hoping it will be just right.

[Brent]

I've got my Leader Inferno arch for a 2-1/2' x 8' in peices to rebuild it. I think the blower in that is 1/4Hp which according to the Grainger catalog, draws 5.2 amps and has an output of 462 to 909 cfm, depending on how much back pressure there is on it. I found another member here who has an identical rig and was asking him how he ran it ( wood consumption etc) and he keeps it throttled way down. Leader ships it with a rehostat so you can control the speed. Then he said he has some neighbours that have an identical rig and that they run it wide open .... and have to rebuild it every other year. They melt down the grates etc etc.

So I'm planning on splitting the output from the blower and having some blast gates ( from Lee Valley ) to control the air flow on each side independantly. One will deliver air under the grates and the other to an air over fire system with injectors in the door and a frame around the door. Then I will add another high pressure blower with 58" WC pressure to inject lots of small jets of air on each side of the fire box ... and that will have a blast gate on it to control the air flow.

Some of the air gassification stuff actually calculates how much energy it takes just to heat the air that we are blasting into the fire box. There is definitely a tipping point where the additional air starts to waste energy heating itself, and then is moving so fast that the stack temps skyrocket and heating of great blue yonder over the sugar shack makes a spectacular show in the dark.

This is why I'm still looking for an oxygen sensor to put in the stack. Keep cranking up the air only until the oxygen sensor start to get active. Once it starts to show oxygen at the stack we can be quite sure we've burned all the solid and gas carbons. Then we'd know we've got enough air and not to add any more. I guess Santa wasn't in a high tech mode this year. Still looking.

PS from what I saw last year on the 2 x 6 Phaneuf, I don't think we need an air tight arch. I still had the draft / ash cleanout door open while I pumped lots of medium high pressure air in over the fire. I "think" it worked great. This year I am sort of forced to blow air in under the grates becaues the Inferno arch
is airtight - no draft control door.