I'm currently constructing my first solid fuel forge. It's a side blast JABOD with a 6" x 6" by 5" deep fire bowl. I plan to use charcoal as my primary fuel, but may give coal a try at some point in the future. I think I've got a good design and construction plan. But I'm having trouble figuring out what kind and size blower to get.

My questions are:

How much air (cfm) do I need to get the most out of the forge with charcoal?

What if I decide to try coal? How many cfm would I need then?

Since I'll probably try to get something a little bigger than necesssry, what's my best option for properly controlling the excess air flow? Blower intake valve? Blower outlet valve? Dump valve?

Thanks for any help you can provide.

It doesn't take much air for charcoal. An inflatable mattress pump is adequate for either. Truthfully I couldn't tell you the CFM required. This is what I used for charcoal but it requires a waste gate or ball valve. It will work with coal as well. 

I use a hand crank buffalo blower now and more than about nine RPM's will blow the charcoal out of the firepot. 

Pnut

Thanks Pnut!

It sounds like even the smallest of the traditional style manual or electric driven blowers will be sufficient.

Now that I know what I'm after, I'll get more serious about my search. I was afraid I might buy something only to find out it wouldn't move enough air.

My very first forge used a dual action hand pump for inflating air mattresses. Charcoal doesn't take much air at all. If you're planning on using anthracite you'll definitely want an electric blower because it goes out quickly without airflow.  

Pnut

 

Got a HVAC repair place near you?  Ask about getting an exhaust assist blower from a super efficient home furnace from their bone pile for a couple of bucks. It will produce way more air than you need but is easy to waste air.

I ordered this vivosun 4" fan and it will arrive in the mail tomorrow.  It is variable speed so dialing it in for multiple forge types should work.  I was using a hvac booster fan with only 100cfm and it would not get the material color past bright orange.  This new fan is twice the cfm and also is a larger 9" centrifugal like the hand cranks which has more push and less backpressure when ash, clinker and whatever tries to clog/block the tuyere.  I cost $50.  excited!

 

Interested to hear how it goes.. Not because I need a blower, but because I generally dissuade people from getting those sorts of in line duct fans. They are designed for, in this case, a 4" diameter duct that is essentially unobstructed. It all depends on the size of your tuyere and your particular forge, but if you try to neck that down to ~2" and fill up your grate with ash and coal, that type of fan just doesn't have the oomph to deliver the air you need. That, or the motor burns out quickly since it's working overtime trying to overcome that back pressure.

Wil, I've seen your forge and it's very different from mine so YMMV.

 

Frazer, this is different from a regular booster fan.  The old 100cfm fan which was regular 4" "almost" worked even after 2x 90degree bends and 10' 1" pipe, I got the material always bright orange and sometimes yellow.  It was 15 watts the new one is around 60 watts.  Yes, there was back pressure and yes there was ash buildup.  This new fan is different, the larger centrifugal 9" flywheel combined with twice the cfm should overcome backpressure and certainly be a large gain from the old fan.  I expect more yellow.  Also the fan blades are spinning so that there is little friction which will also lead to less backpressure, see pic.  Plus very quiet. 

 

 

Ah, that picture makes more sense. I bet that'll work just fine. Sorry, I missed the centrifugal part of your previous post.

Quiet is definitely a plus. 

2 hours ago, Frazer said:

Quiet is definitely a plus. 

That's one thing that the mattress pumps are not. I ended up putting mine in a little styrofoam cooler used to ship medication  that was about a cubic foot interior volume to isolate the noise. 

Pnut

Ear protection is a wonderful thing (I've got noisy blowers both on my coal forge and on the air curtain of my gas forge).

An air curtain is my next upgrade. I never realized how hot a gas forge is around the opening. It's worlds apart from using my charcoal jabod. 

With charcoal I think it would be hard to find an underpowered blower. I'm sure there is one out there that I haven't seen yet though. 

Pnut

Let us know how it works! I’d like a blower like this to pull air from outside for the forge once my shop is finished. I figure pulling air from outside may help with the draw on my hood in winter when I don’t want the overhead door opened all the way.

David

Thanks for all the info and ideas guys.

And Will, that blower does sound like just the ticket for my situation. I'll definitely give it a look.

The David Gingery book on "How to Design & Build Centrifugal Fans for the Home Shop" is very interesting.  It talks about the relation between CFM and pressure, how the rpm and diameter turn into surface speed and limits the max velocity and CFM through the outlet, how to shape the ducts with the same 12 degree taper limit Frosty talks about, how to measure the pressures and speeds, etc..  The whole Gingery series is great.

Larger input watts driving a larger 9" wheel will get you more CFM out.   The sharp bending in the flow from circumferential flow to axial might slow things a bit, but this is designed to be an in-line vent booster.  If you need more air out of it, take a look at the Gingery book and consider modifying it to pick up the flow from the circumference.

pnut: Regarding undersized blowers, I saw a pretty good picture of the range of the imported hand crank blowers.  The 1# blower looks a heck of a lot wimpier than the 5# blower.