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Thread: Hit a cinder block wall, need an exit plan

  1. #1

    Hit a cinder block wall, need an exit plan

    The saga continues: Got the 5hp Baldor 184t frame motor home today after it was rebuilt with new bearings, winding insulation and what they called reconditioned and, come to think of it the guys at the shop commented on the 12" impeller and wondered why such a large framed motor was driving such a small impeller. I think there are a lot of guys in this predicament but I kept the conversation above board. I will have it mounted very close to an external wall tomorrow and there will be about 18" from the rectangular outlet of the blower housing to the cinder block external wall.

    So, I have a 7"x5.6" blower outlet that will be pointing up, paralell to the wall. I want to make a fitting that will allow this to vent to the outside, through the cinder block which requires a change in direction at some defined angle, between 90 degrees and 180 degrees . There are rectangular to round transitions and it can go out in the round via a long radius 8" PVC pipe fitting, it can go out via a rectangular plenum of some form. I imagine there are other ways do do this but I have no basis in fact to make this decision. My Nagyszalanczy Woodshop Dust Control Gospel has no suggestions.

    What is the best way to get the exhaust outdoors? It is so close but then again, so far. Rectangular plenum's are pretty easy to make with plywood on the band saw. Transitions are weird science but can be purchased. I have come this far and I am not in the mood for any compromise in dimensions or shape. Rare earth metals and exotic polymers are not in the offing, but anything sheet metal or plywood is, without question, an option.
    Last edited by Bruce Seidner; 03-02-2012 at 9:37 PM.

  2. #2
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    Sketch it up and take it to your local tinknocker shop and get it done right.

  3. #3
    Would it help if you could cut a hole in the block? Cinder block isn't hard to make a hole through.

  4. #4
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    I can't help it, I resisted last time I opened this thread.

    Exit plan:


    1. hammer
    2. if it doesn't work, bigger hammer
    3. still no exit? repeat step 2
    Of all the laws Brandolini's may be the most universally true.

    Deep thought for the day:

    Your bandsaw weighs more when you leave the spring compressed instead of relieving the tension.

  5. #5
    I sort of soft pitched that one. Ha! A hammer and I thought I needed a plasma laser or something. Oh, you got me there. What was I a think'n!

    No, gentlemen, the problem is the shape and size of the fitting. When I go to the engineering web pages or visit HVAC sites I can't choose between the options. There seems to be two basic strategies. One, you use a rectangle to round transition and then the choice is basically some variation on an elbow with round duct out through the wall. (Said wall having previously been breached with a hammer or in my case a hammer drill.) The other option is a duct or plenum that makes the bend but stays essentially rectangular and the same sized opening with the option to transition to a larger opening making for a tulip shaped duct. I was going to flip a coin, or not give a flip and do what was most expedient, but decided to ask in order to collect flip responses.

    My day has been hijacked and I will not have a chance to do much about this. So keep me rolling in the aisles with the knee slapper's, and I will measure up the transition I need to get made to go to round unless I hear that there is some objectively better way to fabricate the fitting before I get out my hammer. I do have this cool Thor like mini sledge that I get out on occasion, but a bunch of small holes drilled around the opening I intend will precede the banging. But, yes, there is something very satisfying about bashing things and having them crumble.

    Have a great day. After our night of windstorms and the weather radio going out of its little mind squawking tornado warnings it is a beautiful spring morning with clear blue skies and sunshine.
    Last edited by Bruce Seidner; 03-03-2012 at 10:10 AM.

  6. #6
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    Why not keep it rectangular and put in a rectangular elbow? Like you said, make the rectangular duct out of plywood if you want and the sides of the elbow as well. Then the curved parts of the elbow could be sheet metal or masonite? Keep the outlet rectangular after you pas through the wall if you want or transition to round.

  7. #7
    That is what I was thinking but using my thinking rather than physical facts has gotten me into trouble at times. It is such a short run that I was thinking the difference between round and rectangular would not make much difference, but I have been wrong more times than right when going with what my non-engineering sensibilities. I imagine I would just keep it the same size and with as little angle as I can to get it out the wall. The discharge is about 18" from the wall pointed straight up. I will just give it enough bend in the middle to get it over and out. There is no reason it has to be 90 degrees out the wall. I can have it enter lower than it exits and then just cut it back flush to the outside wall. I need to fashion some kind of flap that will lay down over it when the machine is off to keep the birds out.

  8. #8


    The thread title says nothing about Rocket Science.

    So.... what am I missing?

  9. #9
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    Bruce,
    On the outlet, cut a slope that angles about 45 degrees at the end, on the bottom of the duct, and pointing down. You could cover it with expanded metal or some type of screen unless you want something fancier. You may want a better cover if keeping the cold out is a concern.

  10. #10
    Ok, I see, so you are proposing that I modify the end of the blower housing so that when connected to a straight duct of the same dimensions it will exit the wall at some point. Nice.

    I often wonder where to take the hit on a bend or juncture. The other option was to let it go straight for a bit and then take the 45degree hit before sending it out the wall. It certainly is simpler to make a plywood plenum that angles from the blower itself and goes straight and I like the idea of modifying the blower housing just a tad to get a straight run. It is less of a hit. Truly tenacity and guile at work. Much obliged for your thinking outside the confines of the blower as given and creating a blower as required. I like it.

  11. #11
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    While you're at it, put in a window.

  12. #12
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    Quote Originally Posted by Bruce Seidner View Post
    Ok, I see, so you are proposing that I modify the end of the blower housing so that when connected to a straight duct of the same dimensions it will exit the wall at some point. Nice.

    I often wonder where to take the hit on a bend or juncture. The other option was to let it go straight for a bit and then take the 45degree hit before sending it out the wall. It certainly is simpler to make a plywood plenum that angles from the blower itself and goes straight and I like the idea of modifying the blower housing just a tad to get a straight run. It is less of a hit. Truly tenacity and guile at work. Much obliged for your thinking outside the confines of the blower as given and creating a blower as required. I like it.
    Bruce, thanks for the compliments, but I cannot take credit because I am not sure we are talking about the same thing. I was talking about making a square duct that goes vertical, then elbows over out of the wall. Try not to put the elbow directly on top of the fan outlet. You will have a loss associated with the elbow no matter where you put it. However, if it is close to the fan, it will have additional affect on fan performance.

    The angle I was referring to would be at the discharge of your duct outside. If it is going horizontal, then you can cut the end back at a 45 degree angle. This would keep rain out and tend to blow the chips more downward. You could put bird screen on the sloped 45 to keep critters out. I made a sketch but can't seem to upload it.

    Mike

    Mike

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