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Thread: Damper for fresh air?

  1. #1
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    Damper for fresh air?

    I've determined the exhaust method for my shop renovation but am struggling with refreshing the air when it is running. My shop is in the basement with no windows nearby. I was thinking about using something like a dryer vent to go through the wall but not sure if there is some type of damper or other method to keep out the cold air when I'm not running the exhaust. What are your thoughts on a dust collection blast gate?

    Any other suggestions would be welcome.

    Thanks.

  2. #2
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    Homemade version of a Fresh Air Heat Exchanger ... ... ...

    http://makeprojects.com/Project/Heat...1#.UTPV61ePB8E
    FINISHING : NO ART & VERY LITTLE SCIENCE ... just a learned skill that requires a bit of practice and patience ... anyone can learn it.

  3. #3
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    Thanks, Bob. I had not considered a heat exchanger. Great idea.

  4. #4
    we've got something similar to this in our house, since we use a wood stove and the house is extremely tight:
    http://www.americanaldes.com/make-up...ns/airlet-700/

    ours is not thermally activated, it just has a pull cord on the inside that opens and closes the vent.
    Melad StudioWorks
    North Brookfield, MA

  5. #5
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    Ralph, to answer the question you asked yes, a dust collection blast gate would work as it is effectively a glassless window although if cold temperatures are an issue you may want to consider something you can insulate.

    As for the bigger issue you haven't brought up, unless you are planning a <large, sorta> dust collector sized blower to return outside air into your room the vent will need to be large to prevent drawing a significant vacuum in the basement. If you have a oil-fired, gas-fired, coal-fired or wood fired stove, furnace or hot water heater in there the vacuum in the basement will cause the burner exhaust to be drawn back into the basement rather than going up the chimney.

    Drawing a vacuum in the house is a major code deal. When installing a commercial over-stove vent system (~1200cfm) over our range at home we had to add a specialty vent to the outside for make-up air as they were concerned we'd draw auto exhaust from the garage into the house.

    I wasn't part of the install and its in an inaccessible location however it appears to be about 12"-14" in diameter.

    Jim
    One can never have too many planes and chisels... or so I'm learning!!

  6. #6
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    could you use two stove-pipe dampers, you will install one damper and pipe backward so it will open to admit intake of air
    GOD is not dead and American is still alive until further notice

  7. #7
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    Thanks for the suggestions. I'm still not sure what I will do.

    Jim, you made a good point. My shop is in the basement and walled off from the remainder of the basement. It is not airtight; there are a few open (inch wide) areas near the ceiling, but does keep the majority of the dust from the remainder of the basement. I am thinking of using ~100 cfm blower to exhaust finish fumes. The fresh air intake is to replenish the exhausted air. I assumed a 3 inch or so intake would be sufficient for a 3 or 4 inch exhaust duct.

    I'll look into that Am. Alden's make-up intake, Ethan.

  8. #8
    Quote Originally Posted by Ralph Okonieski View Post
    I assumed a 3 inch or so intake would be sufficient for a 3 or 4 inch exhaust duct.
    Actually the inlet needs to be larger than the forced air outlet to prevent creating a vacuum in the house. Your outlet has a fan pushing air. Make up air will take the path of least resistance so it is best to have a larger inlet than outlet.
    Lee Schierer - McKean, PA

    My advice, comments and suggestions are free, but it costs money to run the site. If you found something of value here please give a little something back by becoming a contributor! Contribute

  9. #9
    build a cold trap
    have a vent come into the basement and go to about 3 inches from the floor
    have a box or other tube larger than the vent tube this trap needs to be about 2 foot or taller

    you can buy one if you wish
    http://www.filtersfast.com/P-Skuttle...r-Diffuser.asp
    Carpe Lignum

  10. #10
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    Do you have a door on the basement? I am guessing a basement is not as sealed up as you think. Betting you will just notice loss of heat and an increase in the gas bill.
    Last edited by Mike Heidrick; 03-05-2013 at 6:34 PM.
    Glad its my shop I am responsible for - I only have to make me happy.

  11. #11
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    Typically, a gravity or atmospheric damper would be used for this. It is esentially a damper with a counterweight on the shaft so that it stays closed except when enough negative pressure is applied, it will open, then close back automatically. They come in butterfly or louvered arrangements.

    I'm going out on a limb here, but if you have a 1" gap around the top of your walls, you will likely not go negative enough with 100 CFM of exhaust to affect anything. You haven't stated your finishing exhaust application, but 100 CFM is awfully low and likely not adequate. Also, if this is oil based, laquer, shellac (flammable), I'm not familiar with a fan at that CFM that you would want to put flammable fumes through.

    Mike

  12. #12
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    My apologies for a poor explanation. The one inch gap is between the workshop wall and the remaining interior basement, not the outside. The house is fairly well insulated and comfortable in the winter months.

    My thinking with the 100 cfm exhaust is based on a 150 sq ft workshop. It would completely exhaust the area in 10-15 mins. I'm more interested in keeping fumes from the rest of the house. I could go larger than 100 cfm but still have to reconcile replenishing the air. I am investigating both the intake that Ethan suggested and the cold trap that Phil suggested. The air exchanger that Bob suggested is also an idea to be further considered.

    The suggestions are all welcome and have made me open up my approach to some other thinking regarding where the intake might be located.

  13. #13
    Hi Ralph. As others have stated 100 cfm isn't very much. If you're trying to keep the fumes out of the living area then don't put a make-up air vent in the shop. Slight negative pressure in the shop keeps the airflow moving from the living space, to the shop, then out the exhaust. A strong fan could create negative pressure in the house along with the danger interfering with any chimneys you may have, but I doubt 100 cfm would do that unless you have an extremely small, tightly sealed house. Cracking a couple windows, or having an intake, or cold trap someplace other than the shop when the fan is running would prevent that scenario.
    Mark R

  14. #14
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    I'm with you, Mark, at that volume. A bathroom fan is normally 50-200 cfm.

    I was thinking in terms of a dust collector exhausting outside (higher volume and suction pressure capability than a bathroom fan).

    Jim in Alaska
    One can never have too many planes and chisels... or so I'm learning!!

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