Page 1 of 5 12345 LastLast
Results 1 to 13 of 54
  1. #1
    Join Date
    Jun 2005
    Posts
    37

    Question

    I have sofet vents all arount the house. In the roof I have 3 vents that are like this picture:
    http://www.geocities.com/sp7015/vent.jpg


    Do you think this enough ventilation for a 1700 sq foot attic?

  2. #2
    Join Date
    Jun 2005
    Posts
    347
    it should be ok. if you are concerned with ventilation try adding an attic ventilation fan. relitivly low cost and in most cases its like adding an other half ton to your a/c.

  3. #3
    Join Date
    Aug 2003
    Posts
    626
    Adding a power vent is the worst thing you can do. While I understand Folks in the HVAC service end of the business like to work in cool attics, giving the wrong advice is not helping the homeowner.

  4. #4
    Join Date
    Apr 2004
    Posts
    7,680
    I dont think its wrong advice as long as there is no draw from the conditioned space. The alternative is to use a better insulation on the ducts. A 120+ attic is foolish. Insulation is one thing but you are looking at a 45 degree difference between your home temp and a 65 degree difference between your duct temps. The larger the difference, the faster the losses.

    Why is it the wrong advice? Can you explain?

  5. #5
    Join Date
    Feb 2003
    Posts
    1,996
    Some say the energy used by the fan is a great as the loss in BTU cooling. Maybe a solar power exhaust fan would be the best option. Would only run during the sunny/hot part of the day.

  6. #6
    Join Date
    Aug 2003
    Posts
    626
    Yes it is bad advice because the chances of having an air tight attic in a code buit existing home is nil. Even if the attic was air tight, the energy to run the fan offsets any savings in lowering the heat tranfer. The correct advice would have been to first seal all the holes in the attic. Then make sure you have enough insulation. Sealing the holes has one of the highest cost benefit ratios, because it can be a do-it-yourself project.

    [Edited by uktra on 07-01-2005 at 08:34 AM]

  7. #7
    Join Date
    Apr 2004
    Posts
    7,680
    Respectfully, I must disagree, a sealed attic is not a good idea. They should indeed be well ventilated. Gable ends are better than soffit vents for power exhaust. Soffit vents and either gables or ridge vents are good for natural ventilation. The house should not be under positive pressure and the attic should not be under a negative pressure. Otherwise, this is when you leak conditioned air.

    The drop in attic temp in a ranch home by 10-20 degrees can be a significant reduction in load and cooling requirements and the amperage to run the fan is likely less than the additional compressor requirements to accomplish the same thing.

    Remember the equipment is already installed and the duct is done, I offer an exhaust fan as a viable option at this point.


  8. #8
    Join Date
    Aug 2003
    Posts
    626
    When I said seal the holes, I was referring to the holes between the attic and rooms below. When you put a power vent in an attic you create a negative pressure that does pull conditioned air from the rooms below. In many tests on real homes this was found to increase a/c cost not decrease costs.

  9. #9
    Join Date
    Apr 2003
    Location
    Eugene, Oregon
    Posts
    1,209
    If you have proper ventilating like soffit, ridge or eve vents, a powered fan will not put negative pressure in an attic. That's why they make them in differant cfm sizes. The fans as well as the attic vents should be sized accordingly.
    I agree with the Doc, this is good advice.
    Proud supporter of Springfield Millers and Oregon Ducks.

  10. #10
    Join Date
    Aug 2003
    Posts
    626
    Millerman--That is absurd. Any hole whether from rooms below or to the outside will have a pressure differential on it. And when air comes from the rooms below, the replacement air comes from outside. Tracer gas tests have shown that the infiltration rate of the home increases from 30 to 100% over normal infiltration rates due to power vents.

  11. #11
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    smp7015,

    Did you ever find out whether your system has a TXV?

    I ask this because you seem to have ignored this issue in previous threads. A TXV can really make a big difference in the output of an AC system. This is mainly because many installers don't know how to properly charge a system with a fixed orifice. Overcharged systems are far more common than most pros realize. And an overcharged system won't put out the cool and will cost more to run. The charge is not as critical in a system with a TXV.

    Maybe it's time to call Central City Air and get your house cool before August!



    [Edited by Panama on 07-01-2005 at 12:00 PM]

  12. #12
    Join Date
    Apr 2003
    Location
    Eugene, Oregon
    Posts
    1,209
    Originally posted by uktra
    Millerman--That is absurd. Any hole whether from rooms below or to the outside will have a pressure differential on it. And when air comes from the rooms below, the replacement air comes from outside. Tracer gas tests have shown that the infiltration rate of the home increases from 30 to 100% over normal infiltration rates due to power vents.
    Absurd? Please. If you have an eve vent with an opening to allow 100 cfm and a fan pulling 100 cfm how could you be in the negative and pull air from the living space? As I said SIZED ACCORDINGLY! Power venting an attic is a good idea if all is done properly, your comic book articles may tell you differantly. I'm sure these articles are written about diyers that just slap a fan in without proper venting.
    Proud supporter of Springfield Millers and Oregon Ducks.

  13. #13
    Join Date
    Aug 2003
    Posts
    626
    Yes absurd! a 100 cfm fan is not pulling 100 cfm from one opening if there are other openings. If you don't think a power vent pulls air from below, go buy a smoke pencil and put it next to a non-airtight canned light and watch what happens to the smoke when the pav comes on. Thats not theory, that "in the real world".

Page 1 of 5 12345 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event