Bow windows and condensation

[LD]

Greetings all;

We have massive condenstion on both our bow windows. Not in any of the bathrooms, not in the kitchen, not on any of the original awning windows (dating back to the 60's). The living room has two windows: one awning, one bow window. Condensation affects ONLY the bow window.

I'm beginning to think that the problem could be due to a defective installation - or to a poor-quality product. (We don't know who installed them, or when. They were there when we bought the house.)

We have to replace them (the gyproc underneath is beginning to rot). Can we have new bow windows put in, or would it be safer to go with something that does not project out too much from the wall of the house?

TIA

LD Ottawa, Canada

[m Ransley]

I assume you have dual pane glass. Window glass construction of dual pane is not made equaly by different manufacturers,. Also you may not have Argon filled in your Bay. Even new windows differ considerably co to co. Anderson condense less

- at higher humidiiy than Pella. [ I have both ] Windows are rated for Condensing Factor, which can be found in an old consumer reports article. Condensation is related to R value and construction. Tri pane- Argon - with a modern plastic thermal break will condense the least and have highest R value. Use ratings for a new unit. There is also light tranmittance and solar heat gain to consider depending if you need winter heat gain or your exposure is N S E or west. There is alot of sience to new glass these days, do your research you usualy get what you pay for

[PhotoMan]

What's a bow window?

[Rob Tom]

LD;

Not having seen the specifics of your situation, my guess is that the condensation is due to the fact that since the glass of the bow unit projects out from the inner wall surface more than a "normal" window there is a pocket of relatively still air in the window well (ie the warm air coming out of the register beneath the window doesn't get a chance to affect the air against the glass) so the warmed, moist interior air immediately adjacent to the cold glass lingers for long enough to get cooled to the dew point, resulting in condensation.

The same thing happens to your car's windshield on cool, rainy days in summer or every day in winter and you already know what one solution is: increase the rate of air movement past the glass ( preferably with heated, dry air).

So for the bow window situation, a workable solution (short of replacing the glass with superglass (ie triple-glazed, double low-e films, warm-edge spacers, inert gas fill) would be to re-route the warm air register that is currently on the floor beneath the window so that it directs moving air past the surface of the glass, the bottom-most portion of the glass being most critical. ~~~ * ~~~ Rob Tom Kanata, Ontario, Canada

(w> What's a bow window?

affects

defective

house.)

[Brad]

A bow window is arched in shape when looking at it from above. A bay window has angles between each section of glass.

[PhotoMan]

Thanks - I never knew there was a difference.

[Brad]

Most people just call them all bay windows.

[Chas Hurst]

What does a bow window have between sections of glass. Or is the glass curved? To my thinking a bay window is a flat window extended out from the wall. A bow window is a number of panes forming an arch.

[Eric Ryder]

The previous post re: heated airflow is one part of the problem. Large windows dump heat.

Bow windows are typically casements, which should seal as well as the awnings from the same window order. Exceptions would be 1)large sash with insufficient draw locks (ie 6' sash with a single locking point) and 2) Inadequately supported bow and bay combos often sag from the unit weight and roof construction. This would affect the seal contact. To determine if this is contributing, examine the side (flanking) sash for an out-of-square condition relative to their frames. A 45 degree projection bay with large flankers would be the most likely to exhibit this, a three unit bow with small flankers the least likely.

Also, the head and seatboards of projecting windows should be insulated in heating climates. Sounds obvious, but I've seen it omitted often. This would create a zone of cooler air on the inside of the windows, contributing to condensdate.

[Eunoia Eigensinn]

Eric;

If your comments about "seal contact" are intended to suggest that cold air leaking in around the window sash are a cause of the condensation on the glass, I'd have to disagree and say that the opposite is often the case.

On a window which is fogged up due to condensation, if there are small air leaks present around the sash, one will usually see clear areas on the glass immediately adjacent to the point(s) of leakage, but there will also likely be puddles of water (or ice) below that area too, on the sill.

Even cooler air which is moving fast enough past the glass so as to not linger long enough to reach the dew point, will not result in condensation.

If re-rout>

[Eric Ryder]

I'm thinking more on the terms of a faulty seal (on a racked window sash it will usually be the top that is most noticable) dropping the air temperature over the entire area of glazing, thereby approaching the dewpoint - not complete seal failure and/or a breeze.

out-of-square

[Kai Seymour]

Sort of like a bay window, except usually a minimum of four panels to create a gentle arc as opposed to the trapezoidal line of a typical 3 panel bay.

[Kai Seymour]

A vertical frame. Mine are wood inside with aluminum exterior cladding. They are just a series of flat windows joined at a slight angle to create the arc.

If you have money to burn, one of the big window companies (Anderson, Pella?) offers a corner window that has the glass bent 90 degrees so it wraps around the corner of the building. Very cool look.

[Kai Seymour]

Does it condense all the time? Ours sometimes has a little condensation in the morning but we close heavy curtains at night which keeps the air still & heat away from them.

[Chas Hurst]

I've got a bow window with 6 verticle rows of 5 panes. All set in rather small mullions and mintons or what ever they are called. The previous owner had installed individual second panes made of plexi-glass. I replaced them with 6 low-e framed panes covering the 6 rows. It works well, with virtually no condensation between panes and none on the interior.

I've seen that corner window. As you say, cool. I don't know how long it would last.

Chas Hurst

[Kai Seymour]

I really wanted to use it in the corner of my living room when I replaced all my windows. Unfortunately I have a hip roof house so it would have required cantilevering the headers on both walls. More headache than I wanted to deal with. May not have even been possible with the the 8ft wide bow adjacent to the corner in question. Maybe in the next house (sigh).

[LD]

I would say that it condenses as soon as the temperature drops to single digits (Celcius, that is). Here in Ottawa, that usually means October-November to March-April. As suggested, it could be an insulation problem - the windows are double-panes, with decorative muntins bars sandwiched in between them

- and muntins reportedly lower the R-value and condensation resistance. The seals must be OK, since there is no condensation between the panes - just inside the house. It could also be a size problem: each bow window is 7 floor-to-ceiling panes of glass.

LD