Fan in Gasifier

Hello all.

I’m currently building a downdraft gasifier. Is there any reason to not have a fan? I’m more so asking if it’s required?


Hello Jeremy and welcome to the DOW.

How do you plan on starting the gasifier ?

1 Like

Thank you for the welcome. My plan is to use a torch at the bottom of my reactor. This will be the first one I’ve made in my life and I’m trying to determine if a fan is required. My understanding is the fan creates a vacuum inside the reactor?

1 Like

Welcome Jeremy to DOW. Yes a fan is required to create a vaccum draw to get it started and up to operating temps. Then the engine vaccum draw is what keeps the gasifier going.
When I joined DOW. I spent 100 hours of reading on the different types of gasifiers. Before I started a build charcoal gasifier or rebuild on a wood gasifier. Getting a firm foundation on how they worked is very important.


Thank you so much Robert for the welcome. Does the gasifier need a fan to produce syngas or is the fan just there to imitate an internal combustion engine?

Hello Jeremy .

If your gasifier had been shut down in a proper state and a good char bed You can start up without a fan from motor vacuum . .

You must know before hand that you will be making clean gas because if dirty it will gum the motor .

I would NOT RECOMMEND starting like this but OK for emergence and seasoned operators .


Even if you are going to try and start with just engine vacuum you are going wear out a lot of starters and batteries. Fans are a much cheaper option.


If the question you are asking is if the gasifier requires a fan to operate at all times, the answer is no.

I have started my gasifiers without a fan a lot. 99% of the time its ok. Then there is a 1% when you may get a bridge in the char bed, or the hopper… and you flod the engine with tar. Not worth it, specialy for a beginer.

But lm just ehoing the words of others here.


Wecome to the DOW Jeremy.

Your answer is in your first sentence: you are building a DOWNdraft gasifier.

Heat and hot gases want to rise UP. Not flow down. To force them to flow down will take force/power. To produce the volume of produced gases you will need to force flowS through the woodfuel and char bed pile stacks. They will resist flows.

IF you were building a large footprint stationary gasifier you could set up a minimum 16 foot tall chimney pull drafting from the bottom of the gasifier. You’d have to have it’s own mini-updrafting firebox to get the strong updraft flow going first.
Too big. Too bulky, clumsy. VERY visibly standing up and out.

And you need not a fan (an air mover). . . but a closed housing suction-making blower. Many old systems there were hand cranked suctioned flowed until good enough gas quantity-quality for IC engine running. Then the engine sucking fuel gasses maintains gasifier and filter train flows.
Steve Unruh


You guys are all a great help. Thanks for the explanation from Canada!