Another newbie needs ventilation help!

[glass_affair]

I am very new to lampworking and really appreciate the people on this site - and their generosity with the information they share! I am on the verge of installing a ventilation system - but am really not confident that my plans are optimal. I apologize for the length of my post but I have researched this for a few months now and really want to be safer than sorry – thank you for taking the time to help me out!

I have recently upgraded to a betta with oxy con and will use propane until my natural gas can be piped in correctly (one thing at a time!). Here is the space that I would like to turn into a studio:



I want to turn the computer station into a boxed work station (line it with fire proof material and fabricate a hood that will fit inside the work station ) with a face opening of 38” X 24”. The shape of the hood inside to work station would be similar to this Glass craft model(except that the sides and back would be extended down to the table top). I also plan to make the station deeper - about 30".




From reading Mike’s posts on ventilation, I figure I need a minimum of 633 CFM blower. I plan to vent outside directly behind the workstation ( 1 foot from wall , therefore 2 feet total duct length – no bends).

Questions:
1. What size of fan/ducting? I think that the velocity is either too high (using 6”ducting) or too low with 7”or 8”. Does this mean I should look for a higher CFM blower?(eg 675CFM with 7” duct) Or would 600 CFM be ok with 6” ducting? I’ve read so much about the importance of using a larger duct size but that seems to lower my velocity value. Not knowing very much about these things, it seems that with such a short duct run and so little static pressure…. why would I need such a powerful blower?

2. Is shape of hood vent ok? – and does it matter if it ducts out the side verses the back of the hood?

3. Can the blower be mounted on the outside of an outside wall? I really want to mount my blower on the outside of the house – to decrease noise level but I’m not sure if the blower has to be specifically for this purpose – or can they all be mounted either in or outside . How can I tell when I look at the Grainger web site or any blower specs - what blowers are ok to be mounted outside?


I plan to convince my husband that we need to duct in replacement air (since the window is too close – and not behind me) from the garage – located to the right of the picture (the wall is just cut off). The garage has an open window that would be more than 10ft away from the blower. The replacement air would come up under my work station.

My plan is to locate the propane tank outside the window ( with a quick connect) of my studio and bring a hose in through the window until my natural gas is hooked up properly.

Soooo…. How am I doing???

Thank so much!

Sue

[MikeAurelius]

You've been doing your research, good for you!

You can always go with a higher CFM rated fan, up to about 10-15% over the "design". This allows for trying to find a fan that fits in the range you need, use the "design" CFM as a minimum.

I would go with a standard size duct, go with 8". You will have lower velocity, but increasing the CFM slightly will compensate for that.

Your hood shape is fine, but I am concerned about using the existing table topper as a support for the hood. Because you are dealing with an open flame, wood (or wood products or plastic) should never come in contact with the hood. If you really need to use the topper, be sure to use at least 3" spacers to keep the metal far enough away from the wood to keep possible combustion to a minimum.

Fans CAN be mounted outside. If the fan isn't already weather-proof (and most aren't), you will need to construct a box (preferably metal) to contain and protect the fan from the elements.

From the look of things, in the picture you showed at the top, your fresh air can come in from the window on the far left. If your husband puts the incoming duct on the far left side of the window and elbows it to the left, that should give you the necessary 10 feet.

Looks good to me!

[glass_affair]

Thank you Mike for your quick response! I really feel relieved to know I'm on the right track- thanks to all the information you have posted.

My husband read your suggestion about the replacement air - but isn't keen on using the window - it would interfere with our alarm system etc. (at least this is what he says!) He would rather just have a new vent placed right through the wall on the left side of the picture (no ducts - just the vent in the wall). Is this a good option? My understanding is that this vent should be at least 8" as well - please correct me if I'm wrong.

I understand the concern about the close proximity to the wood on the the computer desk. I was going to remove the back of the unit (since it is only a very flimsy hard board material anyways) and only use metal there. How ever I was hoping to keep the top and sides wood. The whole unit could easily be positioned 4"-6" from the wall. If I left a 3" space above the metal hood between the wood top,would it be okay to keep the width (sides) of the unit flush with the wood? If not, isn't there some kind of product that could go between the wood and metal (on the sides only) that would protect against combustion? I'm just not looking forward to having to decrease the width of my work space to only 32". - and I really want to keep the finished look of the wood on the sides. Any suggestions?

Sue

[MikeAurelius]

Ok - if he's willing to punch a hole in the wall (good for him!), then go with an 8" duct. 10" would be better, but I wouldn't go with 12". Put 1" screen in the opening to keep insects and animals out.

For spacers, I'd use angle irons or something else metallic to keep the hood away from the wood. The issue I'm concerned about is the torch moving and the flame hitting the metal hood - you will have an immediate ignition as the heat is transferred through the metal to the wood.

[glass_affair]

Thank you for the fair warning... I guess I will work in a smaller space - I don't want to mess up now!

So... since my husband is willing to punch a hole in the wall.... he's probably worth keeping! Or were you being facetious?

Sue