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Thread: CFM's

  1. #1
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    CFM's

    Whats the Minimum CFM's for exhaust when balancing a EVR/HRV I know the amount is determined by the number of exhaust point divided by the total amount of CFM's of the unit i.e 200/6= 33.3 cfm per exhaust point but how low of CFM's would be allowable where you would still have proper ventilation ?

  2. #2
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    Wouldn't that depend on what your house needs.
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  3. #3
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    So if my house for sake of argument needs 200 cfm's and I install 10 exhaust points with each point of exhaust having only 20 CFM's that would be sufficient even if one or more of the rooms was 400 sq. ft. ?

  4. #4
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    I always thought that you had to balance the needs of the space the exhaust opening is going into, ie small bath, large kitchen etc with the total amount to be exhausted.

  5. #5
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    Quote Originally Posted by DanW13 View Post
    Whats the Minimum CFM's for exhaust when balancing a EVR/HRV I know the amount is determined by the number of exhaust point divided by the total amount of CFM's of the unit i.e 200/6= 33.3 cfm per exhaust point but how low of CFM's would be allowable where you would still have proper ventilation ?
    I can't say I've ever used that formula.
    As beenthere says, it depends on what the house needs.
    It also depends on what the requirement of each exhaust point is.
    For instance, a large kitchen would require more ventilation than a powder room.
    The HRV ductwork should be sized and installed accordingly.

    Sorry kls-ccc.....I'm a slow typer

  6. #6
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    Now I might understand your question a little bit better.


    Bedrooms would need enough for the number of people.
    Bathrooms as low as 25CFM.
    Common open areas don't need balanced to each other as much. Since natural air currents will help mix the room airs.
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  7. #7
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    Quote Originally Posted by beenthere View Post
    Now I might understand your question a little bit better.


    Bedrooms would need enough for the number of people.
    Bathrooms as low as 25CFM.
    Common open areas don't need balanced to each other as much. Since natural air currents will help mix the room airs.
    There you have it.
    Although the HRV is sized according to the volume of the home, exhaust points are located only where they are needed.

  8. #8
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    Hmm

    Quote Originally Posted by DanW13 View Post
    So if my house for sake of argument needs 200 cfm's and I install 10 exhaust points with each point of exhaust having only 20 CFM's that would be sufficient even if one or more of the rooms was 400 sq. ft. ?
    200 cfm might be 2 or 3 times more than typcially needed for continuous ventilation. See ASHRAE 62.2
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #9
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    Quote Originally Posted by dan sw fl View Post
    200 cfm might be 2 or 3 times more than typcially needed for continuous ventilation. See ASHRAE 62.2
    Good point.
    I haven't seen ASHRAE 62.2.
    But, I seldom see anyone operate their HRV continuously.
    Around here, they are used as glorified exhaust fans.
    Therefore, we size them to maximum exhaust capability.

    And...It's the LAW in these parts.

  10. #10
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    Is ASHRAE 62.2. available for reading somewhere on the internet The full version ?

  11. #11
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    Thumbs up Reasonable ventilation

    Quote Originally Posted by DanW13 View Post
    Is ASHRAE 62.2. available for reading somewhere on the internet The full version ?
    no

    http://www.ashrae.org/pressroom/detail/16048


    Only VERY LARGE home would need > 90 cfm continuous ventilation



    http://www.e-star.com/publications/a...ae_11.2004.pdf
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  12. #12
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    Quote Originally Posted by dan sw fl View Post
    200 cfm might be 2 or 3 times more than typcially needed for continuous ventilation. See ASHRAE 62.2
    I'm not sure if 200CFMs would be too much or just boarder line since both me and the wife are smokers thou it's mostly contained in the main living area and do not smoke upstairs in the sleeping area of the home. I was thinking the Renewaire EV-200 would be just a tad much but am rethinking maybe going with the EV-130 and I am going to operate the unit continuiously and would possibly have the baths connected thou here again I'm thinking of running the baths on a seprate inline fan along with the Kitchen exhaust so I'm still pndering just how to set-this all up.

    If I lose the inline fan idea and run everything thru the EV 130 or 200 and use the inline fan for just the kitchen exhaust so I guess it all depends on which is my best option but am open to suggestion .....

  13. #13
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    Thumbs down Dang - Pollution control is not my fortay

    Quote Originally Posted by DanW13 View Post
    I'm not sure if 200CFMs would be too much or just boarder line since both me and the wife are smokers thou it's mostly contained in the main living area and do not smoke upstairs in the sleeping area of the home. I was thinking the Renewaire EV-200 would be just a tad much but ...
    1. Quit smoking
    2. Smoke outside @ > 14'F
    3. EV-200 is likely N O T too much.
    I would only run noon - 10 pm or to fit your schedule.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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