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James Higson

Propane Fume Extraction in an Ancient Small Shop

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Dear all,

I am soon going to be moving to the beautiful Yorkshire Moors. This means I will be moving the 10 tons of power hammer, anvils and general tat that ive accumulated over the years. Not looking forward to it!

It is a pre 1750s mill cottage in the middle of the moors with an attached workshop which is approx 9ft high, 8ft wide and 12ft long. The issue is that there's nowhere to vent the propane fumes and opening doors is not an option (the roof is too low anyway). I was thinking of cutting a hole in the roof/wall for a pipe and getting an extraction hood for over the propane forges. I have a vertical and horizontal forge I made myself. My question is - does anyone have any experience of extraction apparatus and will it be enough in a small enclosed room with one or two forges running at welding temp with a reducing flame?

Thank you for any help which will reduce the chance of my carbon monoxide induced demise!

Cheers,

James

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J. Arthur Loose forges in a basement (I think).  He has his fume extraction set-up posted here.  

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Sounds lovely, but moving that amount of kit will be less than pleasant...

What's your air inlet situation?  I ask because you could probably run a 12" or larger pipe straight through the roof, put a large hood close over the forges, and if there is enough air coming to equal that going up the chimney you should be fine.  The CO is going to be entrained in the hot air rising, so if the volumes even out you probably won't need a fan.  I'd go with 14 or 16 inch if you can get it.  Drain culverts are good for this if you can find one for scrap.

The other option is a large fan in the wall, but that won't be as efficient.  Good luck with it all, though!

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James, that sounds lovely. Please remember to post some pics of the place when you next get a chance. Good luck with the move.

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Cheers guys, j.loose's setup does look like it's a system tailored to a similar situation! If I were to be able to get some wide stove pipe Alan, I assume I'd be looking for a simple fan to fit inside whatever diameter pipe I get if I wanted to be extra sure it's sucking? I think the air inlet to the space is going to be pretty bad due to the age of the building.

I'll get some pictures Charles! Should look pretty old school hopefully.

James

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Thanks James. I just had a thought about fans. You get some pretty strong in-line fans at hydroponic shops. Might be worth a look too. They generally try to make them quiet. (P.S. I grow chillies as a hobby too).

14FD5212-13D1-4ECF-947B-1EC2340FD5BF.jpeg

 

Here is one makers chart. To convert m3/hr to cfm devide by 1.7 so 1050m3/hr is 618 cfm.

6B3BD4FD-8D9B-4339-A2D1-DB9BB2C94693.jpeg

Edited by Charles du Preez
Additional info

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So-called draft inducer fans are really just small squirrel-cage blowers mounted into a hole on the outside of the pipe aimed in the direction of flow.  I'd suspect a motor mounted inside the chimney might get too hot to work.  But I could be wrong!

Old buildings usually have a fair bit of air inlet, especially when you don't want them to.  Cracks under and around the doors, stuff like that.  You need a little no matter what, because if air can't come in it can't go out either.  Nature not liking vacuums and so forth.

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1 hour ago, Alan Longmire said:

Old buildings usually have a fair bit of air inlet, especially when you don't want them to.  Cracks under and around the doors, stuff like that.  You need a little no matter what, because if air can't come in it can't go out either.  Nature not liking vacuums and so forth.

One of my first jobs was installing industrial paint booths in factories.  They generally had a 10,000 CFM fan for a small  booth with an open front.  I remember early on in that job my boss got into an argument with a plant manager telling him that they couldn't put in another booth without updating the HVAC system.  I didn't understand why at the time, and it didn't matter since the plant manager insisted we do it.

Once we installed it, there was enough negative pressure inside the plant that people were really struggling to open the doors :)

 

 

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Ha, I see your point Alan! From that respect I assume there's some cracks etc so hopefully I shouldn't die from suffocation by pumping all the air out! Hmm, didn't think about it getting hot, pretty big oversight! So the ones mounted on the outside, how do they move air along the pipe?

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They have a hole cut in the pipe and the outlet of the blower sticks in a cm or two, blowing upstream to induce a draft.  And yes, I can't imagine an old cottage on the Yorkshire Moors being airtight.  :lol:  You should be fine once you get there to work it out.

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you will need a decent forge extractor, they normaly have a motor mounted in a split in the flue to keep it outside the hot air, they are expensive. once the flue is hot it willextract well.

I have a forge extractor somewhere and can try and dig it out if you are interested? I think it single phaze , not sure though.

 can you not set up a leantoo or Tin roofed extension for the forge and hammer?

 

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That would be amazing Owen, thanks! How expensive are we talking? The lean-to idea would be great but with the stone-built nature of the workshop and the fact that on one side is a road and the other is an earth embankment I think it would be problematic :(

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The technical term for the fans Owen is describing is "bifurcated" (bif). They are usually "Bifurcated Axial" fans (bifa). It might help you find some details and pricing.

 

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You may not necessarily need to go with an expensive BIF Axial fan.  A centrifugal utility set fan will also have the motor out of the airstream and can often be sourced at liquidators.  You will need to be more creative about the duct runs, as they are not inline fans, but it should still work for you (there are also less expensive inline centrifugal fans that are belt driven, with the motor out of the airstream, but those are less common.  Note that for fume extraction you don't necessarily need to worry, but if you are anticipating any kind of dust (in particular wood dust or a combination of same with metal dust) I would look carefully into spark/explosion proof fans, spark arrestors, a water trap...

A good rule of thumb for capture of fumes is to have at least 100 ft./min. at the crossection of the hood entrance (i.e. if you have a 2' x 4' hood inlet you should pull 800 CFM at the fan and typically use a 12" diameter duct to connect them, the last depending on the external static pressure the fan will exert).

A louver in a window or door will allow the makeup air you need to compensate for the exhaust.  Typical velocities to avoid entraining weather are in the neighborhood of 500 FPM for a conventional louver and 800 FPM for a special drainable louver.

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Thanks Dan, loads of info! I'll have a look at the BIF fans tim thanks and see if they're in my price range. Sounds like centrifugal fan outside the pipe is likely the best bet but if I need Owen's fan or if I can get away with a smaller one without dying is the question. If Owen's is within budget, you can't have too much extraction I  assume?

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As propane is nominally heavier than air, the ideal fume extraction from your shop will have both high and low inlet points to handle both the heated combustion products and a potential propane leak (I burn natural gas, so only have a high exhaust).  I personally have a 20 x 20 shop and use an almost 10,000 CFM, 1/2 HP sidewall exhaust fan and run a ton of air through my shop.  This type of fan is ideal for the application, high volume and low static.  More is definitely better, and my general assumption is that you don't need a hood with a natural gas forge as both the hot exhaust products and any leakage should rise.  My fan is placed in the sidewall of the shop, high up in the roof peak.

You certainly don't need anywhere near that much ventilation, but I find that it also helps keep the shop a little cooler.

 

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