Page 2 of 6 FirstFirst 123456 LastLast
Results 14 to 26 of 75
  1. #14
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    918
    Quote Originally Posted by Carnak View Post
    bay windows are prone to sweating, keep drapes drawn increases the risk of sweating

    A u-shaped condnesation pattern at the bottom will be common

    The high R-value of the glass is based on the centre of the pane

    Sometimes you have a vinyl or wood framed window but the spacer between the panes is metallic so it short circuits the heat loss. corners lose heat in two directions

    I used to tell my customers back home when it was below freezing set the ventilation system to try for 35%, better windows the higher RH you can maintain

    windows tell you when you need more fresh air
    No bay windows and drapes are open too.

    Even using the center of the panes higher temperature, it still would be 20F lower than charts list for Low-E glass.

    What happens to your RH with all this fresh air?
    Bill

  2. #15
    Join Date
    Apr 2002
    Posts
    11,808
    fresh air in the winter lowers the RH in the home, and therefore lowers the dewpoint inside of the home.

    Assume the window has a center of the glass rating of R3

    It is 20F outside and 70F inside

    An estimated surface temperature is 58.7, and you would not see the centre of the glass sweat until you had about 67% RH, the frames and the corners will be colder for reasons already stated and condensation tends to be a U-shaped pattern at the bottom, because it is colder at the bottom corners and indoor air likes to flow up
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  3. #16
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    918
    Quote Originally Posted by Carnak View Post
    fresh air in the winter lowers the RH in the home, and therefore lowers the dewpoint inside of the home.

    Assume the window has a center of the glass rating of R3

    It is 20F outside and 70F inside

    An estimated surface temperature is 58.7, and you would not see the centre of the glass sweat until you had about 67% RH, the frames and the corners will be colder for reasons already stated and condensation tends to be a U-shaped pattern at the bottom, because it is colder at the bottom corners and indoor air likes to flow up
    Your assuming that winter air is always dry and that isn't always so. It's 65% RH at 36F right now outside and my inside RH is 35%.

    By the time condensation forms in the center of these windows at 67%, it would be running by the buckets from the corners! Nobody will be worried abount "when" the center sweats, only where is starts to sweat.

    If they are rated at the centers, they must also go by size and location too. The sliders corner temperature is 5-6F higher than the unmovable pane and the center's temperature is 8F warmer than the corner. Seems like these glass specs are a bit twisted to sound good.
    Bill

  4. #17
    Join Date
    Apr 2002
    Posts
    11,808
    Relative humidity is a confusing term it is relative to the temperature.

    36 F & 65% RH is the same moisture level as about 70F and maybe 19% RH

    Cold air is dry even at high humidity levels, the colder it is the dryer it is
    Last edited by Carnak; 11-27-2008 at 03:56 PM.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #18
    Join Date
    Apr 2002
    Posts
    11,808
    Quote Originally Posted by wptski View Post
    By the time condensation forms in the center of these windows at 67%, it would be running by the buckets from the corners! Nobody will be worried abount "when" the center sweats, only where is starts to sweat.
    it will be typically a U-shaped patttern
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  6. #19
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    918
    Quote Originally Posted by Carnak View Post
    Relative humidity is a confusing term it is relative to the temperature.

    36 F & 65% RH is the same moisture level as about 70F and maybe 19% RH

    Cold air is dry even at high humidity levels, the colder it is the dryer it is
    Right, warm air holds moisture and cold air doesn't. That why RH rises at night when the air cools.
    Bill

  7. #20
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    918
    Quote Originally Posted by Carnak View Post
    it will be typically a U-shaped patttern
    Who cares what shape the pattern is? I had beads of water in the corners at 40% RH with 20F outside, at 67% RH, the corners would be dripping.
    Bill

  8. #21
    Join Date
    Apr 2002
    Posts
    11,808
    whatever I was telling you what happens when it gets cold, good luck with your problem
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  9. #22
    Join Date
    Feb 2004
    Location
    NC
    Posts
    145

    Condensation on windows

    Have you check the glass to see if (1) it is in fact low E (2) the coating is on the right side?

  10. #23
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    918
    Quote Originally Posted by building solutions View Post
    Have you check the glass to see if (1) it is in fact low E (2) the coating is on the right side?
    What's the test for that? I do know that things appear darker when viewed throught the glass. The inside glass is tempered and marked as so on the inside of the panes.
    Bill

  11. #24
    Join Date
    Dec 2008
    Posts
    13
    Hi all...

    I live in an apartment so I'm not sure as to exactly what type of windows I have or their rating... but presently, it's ~30F outside (Massachusetts) and the lead of a digital thermometer I have affixed to the window pane surface is reading 44F...

    This seems really cold, no?

  12. #25
    Join Date
    Nov 2008
    Location
    Houston, TX
    Posts
    77
    The following table shows the maximum levels of humidity at which there will be no condensation on double-glazed windows at various outside temperatures.

    (Dehumidistat settings)

    Outside Air Temp(°C)....Maximum Inside Humidity at 20ēC (68ēF)
    –30ē or below..... 15 percent
    –30ē to –24ē...... 20 percent
    –24ē to –18ē...... 25 percent
    –18ē to –12ē...... 35 percent
    –12ē to 0ē......... 40 percent

    So that's for a regular double pane. 20°F is -6°C.

    Single pane windows are terrible. The 40% figure above is about 19% to avoid condensation. I don't have the chart for triple pane and double pane/low E windows. But they were something like 5-10% higher figures than a regular double glazed window.

    Carnak is right about curtains. In Canada, curtains are supposed to have a minimum 50 mm distance between the curtain rod and the wall. 100 mm is recommended.

    As for the original questions on low E window glass temp. I can't really answer that. I've never had low E windows.

  13. #26
    Join Date
    Aug 2003
    Location
    Florida
    Posts
    50
    As others have stated ventilation is probably the answer. Try and run the exhaust fan in the bathroom longer if you have one, if not get that first. Also on colder nights run the kitchen fan and see if it helps, if so then you know which way to go. Older homes generally are not tight and will allow fresh air in with exhaust running.

Page 2 of 6 FirstFirst 123456 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