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Ventilation In A Small Forge? Answered

Hi all,

Im trying to build a small forge in my small tin shed (9'x11') , due to noise and residential location everything must be inside and the sound proofing makes it pretty airtight, therefore I'm relying 110% on good ventilation design to avoid CO poisoning.

The coke forge is in and flued using the side sucker design and 12" insulated duct, so far this works well with the addition of incoming air from the rear of the shop and I have been able to use reasonable quality test equipment to measure CO at acceptable levels (only under ideal conditions, further testing to follow).

I have also thought of adding a propane forge (only one forge be used at any one time) but worry about the increased levels of CO produced, I have toyed with the idea of a hood which encompasses the mouth of the forge which would be ducted at 45 degrees into the main stack for the other forge (I would like to minimise roof penetrations if possible)

I have made a rough sketch (in paint sorry) to demonstrate what I mean, do you think a fanned draught inducer is necessary/useful, we don't use them much in the UK so im not sure how much draught they induce :),  is the flue angle/ bends going to reduce efficiency greatly and would adding a fan to the intake to change to positive pressure internally make that much difference? 

Any other ventilation advise would be greatly appreciated, including anything to help understand the maths required to calculate correct air volumes etc, I'm fairly serious about doing this correctly, understand in some detail the dangers of CO exposure and would not concider continuing without thorough testing for safety.

Thanks in advance, drawing not even slightly to scale :)



2 years ago

Thanks for the replies,

It is for steel, mostly blacksmithing type activities.

The drawing is not very clear but the flue does extend 4' above the apex of the roof.


2 years ago

If it is not for steel but aluminium and similar you might want to consider electric.
I would not want to go back to gas or wood for melting my aluminium scrap.


2 years ago

If you increase the height of the chimney, it will induce a greater flow of air.

Depending on your local planning regulations and the friendliness of your neighbours, you might be able to get away with extending four to six feet above your roof-line.