Need better condensation resistance than Pella...fiberglass?

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iksea
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Need better condensation resistance than Pella...fiberglass?

#1 Post by iksea »

I have a condensation issue like lots of people. I rebuilt our house and put all Pella Proline windows in about 5 years ago. I went after them because I do not believe in vinyl (toxic issues, expansion issues, expected lifespan) and they seemed to be a good value at about $180/ea (owner installed) for wood/aluminum clad.

They have been OK, EXCEPT for the edge condensation is getting out of control in our Seattle location. The kicker is that I have radiant heat so our humidity tends to be rather high in the winter vs all of the other people with forced air. The wood sashes are painted with latex paint that is turning into total mold/mildew mess. If you open the window, all around the seals is even more mold/mildew. I have noticed that our house usually has 50% humidity at about 69F. I would have thought that our mild Seattle climate would not be a problem, but we do get down into the 30's over the winter and we have major problems as soon as it gets to below 41 outside.

So I would blame the house, not the windows except that I have 2 full lite IG doors that are fiberglass with what looks to be about the same construction with spacers that NEVER have the problem. I think that some of the solution is that the edge spacers are inset more into the door skin and is then additionally insulated by the door skins instead of having the edge spacer right near the frame opening. I would guess that if the frame was a little bigger and the edge spacer was embedded more in the sash frame, I would not have as much of a problem.

So we are going to look into a dehumidifier to turn our comfortable air into yucky dry air, repaint all of the windows this summer with a mildew/mold blocking paint, add additional weather stripping to reduce condensation around the sash seals...a lot of work.

Some of the sashes are already showing signs of expansion from all of the moisture and the wood may be starting to rot on the glass/wood interface.

I am planning a new addition with a stair to the basement and need to buy 5 more windows and do not want to deal with this again.

Who has suggestions on highest edge condensation resistance in a fiberglass window? There are not that many around...Milgard, Marvin, Pella (no way), Fibertec...

I did see that NFRC has a condensation rating for some of the windows, but it may average center vs edge and I really only need good edge resistance since my temp differential is not that bad.

Any ideas?

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Windows on Washington
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#2 Post by Windows on Washington »

It might be helpful if you posted up some pictures to begin with.

Secondly, what is the spacer construction of your current windows. If you are on an Intercept window, upgrading to a non-metallic spacer will increase your IG performance right there.

When you say edge condensation, is this on all 4 sides of the IG or mainly near the bottom of the sash (near the sill) and where the upper sash meets with the lower sash.

If that is the case, then I would also suggest that you have an air infiltration issue that is compounding the problem. When that relatively cold air washes in and combines with the warmer, moist air, you are going to get condensation.

Lastly, you can contact most manufacturers and ask the for testing data on condensation resistance (CR).

Toxic issues aside (that is a whole other post), you expansion issues and expected lifespan issues with vinyl are misplaced.

iksea
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#3 Post by iksea »

I will work on some pictures.

I believe the Pella uses Intercept. NFRC states the spacer as SS-D.

The edge condensation is always the worst on the bottom and halfway up the sides of the casement/awning windows. I have one pair of DH that have it worse at the bottom and also at the middle sash interface. DH definately do not seal as well as casements, so I am going to look into the air infiltration on these since they are the worst.

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Windows on Washington
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#4 Post by Windows on Washington »

The casements should be near airtight. The double hungs I can see not being airtight and contributing to the problem.

I would wait for the next breezy day and get a smoke pencil and see what the air flow near the window is like. Could have air coming around the window or I guess, not likely, air coming around where the IGU is sealed to the sash frame.

That is a metal spacer (stainless steel-dual seal)

Sounds to me like a combination of factors.

tru_blue
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Spacer temperatures

#5 Post by tru_blue »

You didn't mention what type of glass you have. Does it have a Low E coating? The big box stores such as Lowes, Menards, etc. sell Proline windows with or without Low E coatings and with/without argon gas. It can make a significant difference on the presence or absence of condensation. If your windows have Low E with argon gas there should be an etching in the glass that states something to that effect.

As for the spacers themselves, there are aluminum spacers (lousy for condensation resistance) and then there are numerous "warm-edge" spacers (better for condensation resistance). The following are some of the approximate performance stats. These stats are based on an extreme set of conditions: 0° outside and 70° inside the home.

ALUMINUM SPACERS
Clear glass with aluminum spacer = 29°
Low E glass with aluminum spacer = 32°

"WARM-EDGE" SPACERS
Swiggle spacer = 35° (I think)
Stainless steel spacer or Intercept spacer = approx 37°
Superspacer (non-metal) = 39.4°

As for your Proline windows, if you have clear insulating glass, I'm not sure what Pella uses for a spacer. However, with Low E glass they always use a stainless steel "warm-edge" spacer on the Proline series. If you buy more windows from a different manufacturer, if you get anything other than Superspacer, you will not have a significant improvement in spacer edge of glass temperature. And even with Superspacer, it is only approximately a 2° improvement.

I have a few theories as to why the fiberglass doors are not experiencing the same condensation problems as the windows.

1. It could be that the windows are covered with blinds/shades for privacy and the doors are not. When you cover up a Low E/argon unit with some type of window treatment, the glass temperature drops 21°. That's a huge drop. The reason for this is that the air is no longer freely circulating against the glass because it is being partially blocked by the shade, blind, etc. (Again these stats are based on 0° outside). If your windows are covered, and the doors are not, given the humidity level in your home it may be enough of a difference to form condensation just on the covered windows.
2. Similar to the previous issue, casement screens actually block some air circulation against the glass. The circulation in the room doesn't hit the glass at a 90 degree angle; it circulates against the glass at a much shallower angle, and interior screens if left in place deflect some of that air flow away from the glass. Since the casements have interior screens and the doors do not, that can make a difference. Next Winter take the screens out and the glass will be warmer by probably 5° to 7°. Maybe you already did this. Also, if the doors have storm/screen combination doors on the outside, then a key difference between the windows and doors's condensation resistance becomes somewhat obvious.
3. The doors may have a warm edge spacer, and the windows may be clear glass with non-warm edge spacers (again, Proline uses warm edge on Low E windows, but I don't know what they use on clear glass units).
4. Like you had thought, if the glass sinks farther into the door or window, the cold edge effect is reduced. Actually I don't think the reduction is a significant amount, but I've never seen statistics to support this.

iksea
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#6 Post by iksea »

The Proline are LowE Argon and this leads to Intercept spacers. Thanks for all of the contributing factor ideas. We do have cellular shades on some of the windows and these are by far the worst. It is funny that the blind mfg's advertise how much energy they save without telling you that you will be creating a mold growing humidifier on your window if you close your blinds. I have found that opening the top and bottom 2" helps somewhat. The kicker is that I also have blinds on the doors, so I am still trying to figure out why they are condensation free. I am now thinking that the insulated 5" wide frame is able to keep the inside edge of the glass warmer than the narrow wood frame. I was thinking that the fiberglass frames if they are insulated should have a higher interior temp that should help the edge of the IG set. Does anyone know if this is true? The wood sash is also quite cold and sometimes seems to have some condensation, although it is hard to tell since it runs off the glass onto the sash.

I always take out screens in the winter to help the view, so this is not the issue.

I have almost considered getting some tiny solar fans (like the ones you clip on your baseball hat) and putting them in every window in the winter to get some airflow going. This seems to help quite a bit. Or I have also considered getting some adhesive foam tape and lining edge of the glass near the sash to see if this improves things. It would be ugly, but not as ugly as black mildew.

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Windows on Washington
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#7 Post by Windows on Washington »

He mentioned the SS-D spacer designation. Stainless Steal-Dual Sealed.

Did not even think to ask about Low-e/argon as I figured a person that was familiar with the NFRC ratings and concerned about the toxicology of vinyl windows would certainly opt for the more efficient glass.

Good point about the blinds Tru. Often overlooked issue with airflow.

Insulating the frame will increase the CR of the window but only minimally as it pertains to the glass on only right at that union with the glass.

iksea
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#8 Post by iksea »

I was just thinking some more about spacer/sash geometry. Why would the vendors not just make the IG unit 1" bigger and set it inside the sash by 1/2" more? This would allow the coldest part of the glass (the spacer) to have an additional insulating layer in from of it (the thickness of the sash) and seems like it could solve edge condensation...which sounds like it is a big issue based on the number of FAQ sections all of the mfg have on their websites.

Aside from possibly having to have a thicker sash frame (and smaller visible area), why doesn't anyone do this?

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#9 Post by Windows on Washington »

iksea wrote:I was just thinking some more about spacer/sash geometry. Why would the vendors not just make the IG unit 1" bigger and set it inside the sash by 1/2" more? This would allow the coldest part of the glass (the spacer) to have an additional insulating layer in from of it (the thickness of the sash) and seems like it could solve edge condensation...which sounds like it is a big issue based on the number of FAQ sections all of the mfg have on their websites.

Aside from possibly having to have a thicker sash frame (and smaller visible area), why doesn't anyone do this?
Same reason that gasoline stations used steel tanks instead of fiberglass.... :roll:

I wonder what happens when you bury a big chunk of mild steel in the ground without cathodic protection...rust maybe.

It is probably the shortsightedness of most manufacturers but Low-e was such a huge leap and now with true warm edge spacer systems, the glass performance can be even better.

There is certainly and aesthetic component to you question as well as a manufacturing cost associated with it.

tru_blue
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Two things

#10 Post by tru_blue »

Iksea I don't think you know what an Intercept spacer is. If you have Proline windows you do not have an Intercept spacer. An Intercept spacer is U-shaped. Proline does not use Intercept. They use a rectangular shaped spacer that is stainless steel from Cardinal. And Intercept is available in more than one type of metal. Not that it matters much in this case because both Cardinal's SS spacer and Intercept have approximately the same edge temperature performance.

As for sinking the glass farther into the sash/door, I don't know if it has been established that doing so makes any significant difference. I'm not saying it doesn't make a difference, but I've never seen test data from anyone to document the difference in edge-of-glass performance. Can anyone out there confirm? (Sounds like a good one for Oberon)

Oberon
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thinking deep?

#11 Post by Oberon »

From a joint Canadian and European study on the performance of various window spacer / edge systems:

“Conclusion

The thermal resistance of the spacer bar material influences the glass temperature at the edge-of-glass region of an IG unit. Based on the limited testing performed at IRC and computer modeling at EMPA Switzerland, the spacer bar with the highest thermal resistance shows the warmest glass temperature on the warm side and the coldest temperature on the cold side of the glass at a distance 5 to 60 mm from the edge of the IG unit. But the effect of the type of spacer bar on the overall thermal resistance (and tote heat loss) through windows depends heavily on the window design and material. Therefore, the full impact of thermal characteristics of the spacer bar material on the thermal resistance and the condensation resistance of a window should only be determined by testing complete window assemblies.”
emphasis mine.

Very often (almost always), when spacer manufacturers compare thermal edge performance between various spacer systems, they do so without regard to the window sash and framing material - or as to how the IG will be installed into the sash. This is not an accident since the sash material and install method will affect the edge thermal performance of the IG, and the folks advertising their spacer's performance want to advertise the maximum benefit of their system without regard to outside influences - particularly when those outside influences may potentially negate some of their advertised advantage.

This really isn't that much different than using center-of-glass R-values to advertise window energy performance. While these are valid numbers, they may not tell the whole story.

Just as the "how" of the installation of a window in a home can make a huge difference in overall performance; so can the installation of the glass package into the sash make a difference as well.

Installing the IG so that the edge is "deeper" into the sash will add a bit to the overall energy performance of the unit - and it may also tend to minimize the edge perfomance advantage of one type of spacer system over another. And while there may be potential thermal advantages in setting the edge of the IG deeper into the sash (depending on sash material, mounting system, etc), there are also a few technical reasons as to why window companies don't do so.

There is also a definite aesthetic reason as well...when the spacer isn't at the edge of the sash / glass interface, it looks very odd. To most folks it is not aesthetically "pleasing". It would be somewhat comparable to having interior and exterior muntin bars on a window without a corresponding spacer between the lites in the IG unit. Some folks really dislike that "look".

Stephen Thwaites
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#12 Post by Stephen Thwaites »

Europeans seem to bury spacers more than North Americans. For interesting examples Google 'fenster' or see:

http://www.rehau.de/files/Architekten-P ... 793710.pdf

Looks like they're burying their spacer about 15mm (1/2"+).


Did a quick FramePLUS run (Canadian approx. equivalent to THERM). On the run i did, burying the SuperSpacer 1/4" deeper than flush warmed up the edge 4 degrees F. For authoritative results you'd need to do more than a single run........

I suspect most manufactures don't like burying spacers for asthetic reasons - defects in sealant/tape/gasket are too easy to see.

windowmann2000
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#13 Post by windowmann2000 »

ST That site is in German, do you have a link in English? After reading the above post I looked at a couple of Milgards and noticed when they used Intercept the spacer was buried about a half of an inch down but when using Super Spacer it was closer to flush. It does seem the farther down you bury the spacer the better the edge temp would be. Anyway an interesting subject, thanks all.

Stephen Thwaites
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#14 Post by Stephen Thwaites »

wm2000:

checked Rehau's UK and North American sites and couldn't find a english version.

Did find another window w/ spacer recessed even deeper - my guess is 1 5/8" !!

http://www.e2a.de/e2a/img/aktuell/20050 ... inplus.pdf

This is what most would call an aluminum window (although clearly there's multiple polymer thermal breaks), yet its whole window U is 0.79 (W/m^2 K) or in perhaps more familar units 0.14 Btu/ft^2 F

This and many others, including Rehau's Clima, meet the 0.80 (0.14) threshold for the 'Passiv Haus' standard. Clearly, these windows are very different from what we are used to here. And clearly recessing the spacer is only one of their approaches. But at the end of the day these windows insulate very very very well.

I'm told that 20% of the new houses in Austria will be built to this standard in 2008.

So to drift even farther off topic, it's a bit rich to hear Canadian and US manufacturers complain that E-Star is already stringent enough........

Oberon
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#15 Post by Oberon »

Stephen,

That is a great illustration. Thanks for the link.

As a general rule, I think that North American's tend to prefer the look of narrower and slimmer or simply less "beefy" sashes in their windows when compared with European designs.

Unfortunately, it is obviously more difficult to recess the edge of an IG unit into a thinner or lighter sash component and still maintain the required structural rigidity of the unit.

And while it could certainly be done for many designs, I would suggest that in many cases it would require a significant redisign of current assemblies. This isn't something that many companies are going to undertake without a substantial bit of evidence suggesting that they are going to make back their investment.

What is interesting though is that impact windows - intended for hurricane code areas - often do increase the depth of the glazing reglet so that they can recess the IG further into the sash in order to get a more substantial "bite" on the IG to pass the impact / pressure cycle requirements.

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