What are the winter lows? i89 is great stuff but will have a slightly lower CR number as compared to a standard, soft-coat, double pane Low-e equip window. If you don't have any humidity concerns, the point is moot and get the most efficient window that you can.

I'm really new to this. What does CR stand for? Average winter temps are generally in the high 40s/low 50s but this winter hasn't been average. We're expected to hit 70 on Saturday. Not good for the snow pack at all, which is already at record lows. Going to be a bad fire season. But that's not what you're asking. Here are Portland temp & precipitation averages.

I grew up using humidifiers in winter and de-humidifiers in summer in the Midwest but despite our rainy winters and dry summers, we've never had any need for such machines here so I don't think we have any humidity concerns. We did have window condensation issues in our first house, built in '89. Those were dual pane but not low-E aluminum windows. It was particularly bad our first winter (we moved in in late Oct) so that could have been a factor of the newly built house drying out and nothing else. We did not have any issues like that in this house (moved in in July, low-E vinyl windows).

Thank you for your help!

CR = Condensation Resistance

Thanks for clarifying what that means. Any additional feedback for me regarding I-89 windows?

They are great if you aren't in a condensation prone area. Aluminum (your previous window) is prone to sweating so I would not compare a well insulated frame to an non-thermally broken aluminum window.

I have no idea if I'm in a condensation prone area. How do I find that out? I saw some technical data (perhaps posted by you on another thread) but it was too technical for me to formulate an answer for my situation. Thank you, again, for your help!

Temperatures in the winter and what are your relative humidity levels inside the home.

Jeld Wen Condensation

The DWM article on surface 4 condensation. For the record, I know a Cardinal engineer who has remarked that the concerns on surface 4 condensation are probably overblown as he has not seen it as an issue in his dealing. I trust him implicitly as well.

Just giving you all the information that I have so that you can arrive at your own conclusions.

DWM article on Surface 4

Thank you for the additional information! I'll read both shortly. I've talked at length with someone at Energy Trust of Oregon but he was fairly unfamiliar with the ins and outs of 4th surface windows. However, he has two experts in the field that he can contact so I hope to get more information from him as well. Between all these sources, we should be able to make an informed choice.

Thank you again!

http://www.cardinalcorp.com/technology/reference/loe-performance-stats/

Scroll down and compare the stats. SunCoat Max is the same as "LoE3-366(#2)/Clear", while SunCoat Max with i89 is the same as "LoE3-366(#2)/i89(#4)"

Thank you, ef_houseman! Between the info you provided and what WoW provided, I'm learning a lot about windows. I'll be better prepared for a return visit to Milgard's showroom.

I'm surprised, though, to see that the Visible Light transmittance for "LoE3-366(#2)/Clear (SunCoat Max) is higher than it is for LoE3-366(#2)/i89(#4) (SunCoat Max with i89). The latter on display at the local Milgard showroom was noticeably less tinted than the former. In fact, that is one of the selling points for us: better energy efficiency with more visible light transmittance; a plus during our gray, cloudy winter months.

Lisa - I am a little familiar with the climate in Portland and I really question the need for 366 on your south facing windows much less the addition of the i89. Unless those windows get zero protection (no overhang and or shade trees) in the summer, I think standard low e is what you would be most satisfied with.

Thanks, eastbay10, for your feedback. Our upstairs windows don't get a lot of shade, unlike our downstairs windows, plus we have a lot of windows that face south and west, so we may benefit from a lower U-value on those windows.

We're waiting to get a quote for Milgard's 3D SunCoat windows from our window contractor but given that we end up ahead by about $700 if we buy 4th surface windows versus 3D SunCoat Max windows, thanks to tax rebates from Energy Trust of Oregon, we may go for the more efficient windows anyway. Hard not to do the upgrade if it's the cheaper alternative.

Does anyone know what U-value our existing 21 yr old, vinyl, lowE windows might be? I'm sure replacement windows, even the basic 3D SunCoat, will be a gain in efficiency but I've no idea how much of a gain we'll get.

U-Factor out of a 20 year old (non-Low-e) window is probably a U-Factor of 0.55 at the lowest and maybe as high as 0.65.

The bigger issue is probably the air leakage.

Low-e 366 is not correct in my estimation either based on your climate data. You want as much passive solar as you can get your hands on in that climate.

Thanks, WoW, but what I wish I could find out is what the U-Factor is for my 21 yr old, double-paned, low-E windows. My best guess is that it's somewhere between .55 and .40 but that's purely a guess. Our windows are of a lower quality than other brands. We've had to replace at least 5 windows due to failed seals; one of them has failed again.

We're replacing 6 windows as part of an upcoming kitchen and DR remodel, plus the one window with a failed seal. We also have 4 windows with spring issues. They aren't easy to open and close, plus they make a racket when we do and I'm really tired of dealing with them. The other issue is that our existing windows have very little UV blocking. Since we plan to stay put for at least 10 more years and since we're replacing nearly half of our windows already, we fell for the "while we're at it" scenario and decided to replace all our windows.

WoW, why do you think that we'd be better off going for as much passive solar energy as possible? At the time of year when passive solar heat would be great to have, we don't see the sun as much as we'd like. We do get lots of sun in summer. I grew up without AC in the Midwest (was well into high school before we got AC) so I know all the tricks to keeping the house as cool as possible in summer. However, even doing all of that, our upstairs gets really warm and our AC has to work hard to cool it down for
comfortable sleeping. We can't open our windows to cool our house as often as we used to because too many neighbors have fire pits. My asthma and wood smoke are a life-threatening combination. I hate not being able to open our windows to cool evening breezes but I also prefer to stay out of the ER. Anyhoo, that's why we want to avoid passive solar heat gain as much as
possible in summer.

btw, we're already ruled out Milgard's 3D Max windows (low-E 366) because of its percentage of light transmittance. My best guess is that our current windows' VLT are 75-79%. A 66% VLT would be too great a drop for us, especially in winter.

I just did a little experiment. I took our indoor thermometer and stuck it on a sunny window sill in my FR, out of direct sunlight, for 5 minutes. It's 62 degrees outside (we're having unseasonably sunny, warm weather). The temp by the window is more than 6 degrees higher than on the opposite side of the room, 74.9 versus 68.5. I moved the thermometer 6 feet away from the window (close to the center of the room) and out of direct sunlight, and left it for 5 mins. It registers 3 degrees cooler.

Next I moved the thermometer to the LR, which is north-facing with vaulted ceilings. Its always cool in winter. Temp registered slightly cooler than the starting temp in the FR.

So we reap some solar heating benefits in winter in the kitchen and FR and the upstairs bedrooms. Since we prefer to sleep in a cool room, that's not a plus even in winter. And it's definitely a negative in summer.

Thanks for prompting me to think about this issue.

Good luck with the project and keep us posted with pictures and updates.

Thank you, Lisa, for the very helpful decoder chart!!