Air (AUF) ducting questions - how, what, where?

[TimJ]

I am building a small arch for a 2x2 pan and have a little dayton squirrel cage blower. I am not sure of the best way to make a transition to the output/opening of this fan into the arch.

I had read a bunch and was thinking of making a "T" just inside the read of the firebox, then coming forward with 2 black pipes and drilling holes along the top so that the bottom of the firebox, under the grates, would have 2 pipes, maybe a foot apart, traveling from the rear to the front, with holes pointing up.

I did not want to mount the blower right to the back of the firebox since I expect that would be a bit hot.
I do plan to use arch board/insulation, then brick over that.

I have not seen many pics of the plumbing from the fan housing to the air.

I'll keep looking but appreciate any hints or references


This is the thread with pics of my build so far.
I will post a pic of the blower when I get back home

[Sugarmaker]

The fire box below the grates may not get too hot? You could put a extension of a foot or so out the back then mount your blower to the underside of the arch.
Many options too. You can do all that extra plumbing but I dont think it has a lot of value. I would just dump it in the back same size as the blower output dia.
Regards,
Chris

[raptorfan85]

Mine just dumps under the fire grates. With a squirrel cage blower they don't make any pressure so the ducting actually hurts more then it helps because it restricts the air to much. I have a blast gate but you could mount it the same way. I used 4 inch exhaust pipe and welded a square flange on it to mount the blower to. That way it sits back from the hot part of the arch.

IMG_20180909_152943709.jpg

[phil-t]

Yep.dump it into the arch under the grates. No tube or ducting inside. My HalfPint came with a DIY AUF, squirrelcage fan into a draft door replacement and a tube inside with holes, the length of the fire box. I was advised, on here, last season to remove the inside duct. Made a huge difference in the fire. I went from 6 to 8 GPH.

[maple flats]

Agreed, if it was a high pressure the extra ducting would make sense, but not with a squirrel cage. You do however want to block off the front 6" of the grates, in front by the door so the air is pushed up thru the wood. In your case, a squirrel cage is the right blower to use.
Dave

[TimJ]

Thanks all!

that makes it easy (er).

[TimJ]

Any suggestions or pics on how people broached the "firewall" and penetrated brick and/or insulation and kept air tight integrity?
Am I making too big a deal of this?

My concerns/uncertainties are

- heat and ash pushing into blower. To mitigate I may create a tube/duct/offset so it is not right at the firebox wall
- Best way to come through the skin of the firebox and insulation layers and keep it as airtight and heat insulated as possible

I don't have a brake to bend metal - I think if I did I could bend up a conduit and solve this really easily and weld the seams

The simple way to go is just butt the place where the thing joins the firewall and cut out the opening

A more elaborate idea is to "frame out" the opening and weld all the seams/edges. This may be more work than it is worth

[Chickenman]

I have a Mason 2x3 hobby that I got the AUF kit for. Bill included a template to mark the hole. It is just a hole (square to match the blower) in the back of the ash box under the grate for the firebox. Every now and then you can hear the ash/coals being blown into the flue pipe. When that happens I know that I have the blower a bit to high, but I like the HOT fire it produces and increase in boil rate.

[maple flats]

No pics anymore, but mine enters thru the back at floor level. On mine it is just a 4" heavy galv. duct pipe (22 Ga.). It goes thru between some bricks used to fill a gap there (My arch has a 4.5" deep trench under it and the arch rests on the sides. The trench was just a bad plan, but I have not yet cemented it in. The 4" pipe is mostly sealed is is far from air tight, but my AUF is run off my High pressure AOF blower, and it works well).
To bring yours in under, just cut a hole the right size and push the pipe thru. If desired to make a good seal, just use high temp silicone.

[phil-t]

Yes, I forgot to mention that I blocked off the space at the front of the grates, between the door opening and the grates. I may try blocking some of the grate space, as recommended, by Dave.