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  1. #1

    Need help, don't understand cfm50

    Can someone point me to some literature or explain cfm50 to me. I've recently had a energy audit on my home because it is freezing in my master bedroom, and I wanted to see if they could find any air leakage that may be casuing this, and the report bascially told me there is nothing to be done, because my house was too tight.

    The results of the blower door test is that my house is at 3210 cfm50 and that if I go any lower that I would be violating some sort of air quality standard. They said the opitimal levels are 4131 cfm50, I've tried to do some research but I can't really find anything about a standard, and what I have found is that, the tighter the better, and that you would need to dip below 1000 cfm50 before you would require putting in a mechanical ventelation system.

    One l link that I reviewed from this site: http://www.pct.edu/wtc/docs/articles...Door-FINAL.pdf states that 1,500 is tight, between 1,500 and 4,000 is moderate.

    This company seems a bit shady, and I feel that the informatoin that they have provided is not accurage or skewed. Could anyone shed some light on to this I would appreciate the help.

  2. #2
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Thread relocated to AOP

  3. #3
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,700
    Is the only problem you're having is with the bedroom being too cold? How old is the home? Is it a ranch, split foyer (with the garage under) or a two story? Do you have a basement, slab or crawl space? Where is the furnace located?

    Fixing that problem is probably ductwork related or insulation related. We put in the system in a new home and they couldn't heat a bedroom. As many here can relate, the first to get blamed, is the HVAC guys. Long story short, we found the insulators forgot to insulate that part of the attic.

  4. #4
    Join Date
    Sep 2008
    Location
    New York
    Posts
    131
    3210 CFM50 means almost nothing without first knowing the size of the house.

    Example- if you live in a 1200 sqft ranch with 8 foot ceilings. 3210 CFM50 would indicate that the air in your home will exchange with outside air approximately 1 time every hour. This would indicate your house is pretty leaky

    if you live in a 7000 sqft 2 story with 9 foot ceilings. 3210 CFM50 would indicate that the air in your home will exchange with outside air approximately once every 5 hours. This would be a well sealed home and it my not be cost effective or practical to make it any tighter.
    "The only way in which a human being can make some approach to knowing the whole of a subject is by hearing what can be said about it by persons of every variety of opinion and studying all modes in which it it can be looked at by every character of mind.
    No wise man ever acquired his wisdom in any mode but this."
    John Stuart Mill

  5. #5
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,188
    true. size of house & blower door reading are important numbers.
    #cubic feet per minute tested at 50 pascals, doesn't tell us much,
    nor apparently did it tell you much!

    sad that the company didn't explain & answer your questions
    to your satisfaction.

    did they test ducts for leakage? inspect insulation in attic?
    any comments as to why bedroom was colder?

    do you have recessed lights in this bedroom?
    how many supply grills, and how many returns?
    is return in the bedroom, or located in house somewhere
    else?

    what was the process?

    are you in Pa? ( link is pa info..which is why I ask)
    if not..where are you located.

    answer our questions and we will better be able to answer
    yours.

    sorry you had a bad experience with this company.
    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  6. #6
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    @energy_rater_La

    I'm curious why the energy rating and home weatherization industries settled on 50pa.

    At my company, we use a blower door for measuring and finding leakage to repair, but we only test at 25pa.
    We don't participate in any programs, or even have the certifications needed to participate in them, just an HVAC contractor fixing stuff as part of what we do to make the house work better.

    I've tested houses at both 25 and 50, and gotten nearly identical leakage area results.
    I've also tested homes at 25pa, that were also tested by a HERS rater at 50pa, and gotten very similar results, within the margin of error you would expect to see comparing any 2 tests on the same house.

    There may be something to it that I haven't seen yet, but the only difference I've seen is that 25pa will reveal leaks in the weather seals between double hung windows, but 50pa will make them buzz.
    If more government is the answer, then it's a really stupid question.

  7. #7
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,188
    I'm not exactly sure why Mark.
    I think that they just chose this number to standardize both state & federal testing pressures.
    and, that 50 pa is enough to accurately measure leaky houses without doing damage.

    whole house test @ 25 doesn't show enough of the leakage sites.
    whereas @ 50 pa, it will.

    also 50 pa won't usually pull ceiling tiles down in low income weatherization houses where
    they may be falling off the ceiling.
    weatherization wanted us to do preliminary, intermediate & final blower door.
    these multiple tests done prior to, in the middle of, and at the end of the project
    allowed large holes to be sealed, then medium and smaller holes would show up.
    hopefully, by the third test..most of the leaks were addressed.

    in very leaky existing homes can't reach 50 (pa) factor is used.
    these very leaky homes may only reach 15 pa, so a multiplication
    factor is used to determine leakage. at 15 pa leakage isn't 1,000 cfm..
    but 10,000 cfm (for example)

    have you ever tested a very leaky house & used cr50?
    or a house so tight you had to use ring a or ring b?

    you have a real wth?? moment...and then..use multiplication
    factor, or add a ring.
    I did both and recorded both numbers.
    just to cover all bases. LOL!

    I once emptied out a house of kids in their bedroom when I set up the
    blower door & their window wasn't closed properly. they thought
    it was a ghost. the window started off as a moan..then rose to a
    whistle...big eyed kids running for their lives..it was too funny!
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  8. #8
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by energy_rater_La View Post
    or a house so tight you had to use ring a or ring b?
    I've tested houses that were so tight I had to use C4 on our Retrotech 2000 fan to keep the fan speed above 30%.
    I've also tested houses so loose that the fan was running at over 90% with no rings at all.

    I once emptied out a house of kids in their bedroom when I set up the
    blower door & their window wasn't closed properly. they thought
    it was a ghost. the window started off as a moan..then rose to a
    whistle...big eyed kids running for their lives..it was too funny!
    The only "creepy" type thing I've had happen was with poorly installed double hung windows. Enough air was being pulled past the seals, at just the right velocity, to make nearly every window make a low buzzing sound. The inside of the house sounded like there was a very large beehive nearby.

    I've had a couple of minor leaky can light + cellulose insulation disasters. Fortunately the customers didn't get too upset, and it served as a graphic demonstration of how bad can lights leak, no smoke puffer needed.
    If more government is the answer, then it's a really stupid question.

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