A simple side draft flue

[pragtich]

I was driven to action the last months, due to the rainy spring that we have had here in the Netherlands. Good for the farmers, but it kept me from enjoying the open air setup that I was using. So it became time to install the flue that I have been planning for a year now, into the shed.

I figured that it might be helpful to share an experience, perhaps it might help someone out.

Having originally planned to go through an available masonry channel, I had purchased some 250mm single-walled stainless flue pipe. That didn't work out: the channel wall was too irregular to fit. Reading on this forum told me that 250mm or 10" is considered to be the minimum feasible diameter. So I changed the plan to a through-roof solution and it turned out surprisingly nice.

In total I used 5 x 1m length of 250mm pipe, 2x 45 degree corners, a rain cap designed for wood stoves an a blind cap at the bottom.

For the side draft opening, I chose to follow the sizing that was published by Jim Guy for his 10" Super sucker, which uses an 8 1/4" (21 cm) square opening (89.5% of the flue area). I simply cut two doors in the side of the lowermost tube, just above the end cap ~3" above the level of the forge table. This will need some finishing as the walls are terribly thin and sharp.

I did a test firing this morning, and it really is surprising how well the flue draws. I started the draft with a small paper fire in the bottom of the flue, but I doubt that it's really necessary. In contrast to experiences from others, it seems that my standard rain cap is sufficiently open to allow for good draft.

The only smoke that escapes, is the smoke that gets wafted out of the fire by my movements, or by wind gusts through the open window.

All in all, I'm really happy with this solution, so I figured that I'd share.

[JHCC]

Very nice!

On a side note, that’s an awfully big motor you’ve got running the blower. How do you regulate the blast? 

[Latticino]

You might end up wanting to reinforce the opening with some thicker sheet steel.  All the super sucker inspired hoods I've seen get very hot at this opening over time.  Your thin steel will get hot and start to scale away (even stainless).

[pragtich]

3 hours ago, JHCC said:

How do you regulate the blast? 

Haha, it is indeed a significant motor. You should have seen the motor it came with, that one was even larger! Still, an induction motor runs a fixed rpm, so the pulley sizes determine the speed of the blower. I made up a (wooden) motor pulley that got me roughly in the ballpark.

It seems that the previous owner put a motor in when the crankshaft for the pedal drive had worn down too much. It looks like they were using the clinker breaker as a crude gate valve. They added a locking screw in order to be able to set it to a fixed position. Since it closes quite tightly, that works (sort of).

I went for a more high-tech option and installed a small VFD that I had gathering dust. Very satisfying :-)

[pragtich]

Ah, Latticino, just noticed your comment.

Yes, I'm sure that's what's going to happen. I'll be building a proper steel box some time in the future, I'm sure. But a helpful proof of concept for the flue, and it might last a little bit.
Thanks for your comment.