Ridgewayforge

Forced Air Ventilation vs Open Doors/Windows

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Greetings- 

I recently bought a townhouse and in the small back lot it came with a block shed, around 12x10x14 (gabled roof). There is a front man-door and two 3x1 windows. I know that I will need more ventilation than this; I will be using a Sandia Labs Recuperative Gas Forge. 

The block goes up to about 10ft", above that is wood on the inside, siding on the outside. 

My plan is to cut two ventilation holes on either side of the building, with the rear side (opposite the door) having a bathroom vent fan bringing air into the shed. 

 

My hope is to avoid death by CO. From a first glance, does this sound rather dangerous, or might I be alright with this plan? 

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Think of the needed air changes of the room per time period.  More is better than less and a CO detector is a must.

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Is there a general rule for how many air changes per hour there should be? That would determine my CFM, in turn helping me choose an exhaust fan type. 

Additionally, my thought would be to have the fan pull air INTO the shop. Given the air changes neeeded, of course. 

Is there any benefit for the fan pulling air IN vs pulling the CO out? 

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Better to exhaust air out than pull it in.  Push it out and all the bad air is going directly toward the exhaust fan.  Pull it in and it'll sort of have to "hunt" for the exhaust vent...............if that makes sense.  Always better to have a large exhaust fan.  I'd recommend an attic fan one often sees in homes.  Just mount it horizontally in a wall higher up.  I wouldn't exhaust through the ceiling into the attic (if you have one) because it might not find an adequate way to exit the attic.  I'm no expert, but that's the way I'd do it.  We had 2 6' exhaust fans in our business and they were mounted that way.  Worked great.

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As others have said, gable end fan...and preferably oversized.  Those can be pretty easily throttled with a standard "dimmer" because they drag the air over the motors so aren't likely to overheat.  I see one on the big internet site that does 1280 Cfm which would be about an air change about every 2-3 minutes (less when throttled)  Price with the speed control and an auto thermostat is less than $ 150 (including frame with louvres).  Only 1/20 HP so it's not going to kill you on your electric bill or power needs.

Smaller available also but it's better to have too much than too little.

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