Window air tightness- various questions about brands and styles
We are planning an energy efficient house. Climate Zone 5b
Architect’s energy modeling software has shown that for our zone and solar intensity, air tightness is pretty critical for managing cooling load but we don’t need anything extravagant in terms of R-value for the envelope. To the point that we can be comfortable with double pane windows.
I am having decision fatigue and haven’t had much time to look at windows yet. Would like some thoughts.
Casement or fixed windows all around currently, hoping for lift and slide for patio door.
Builder’s default is Jeld-Wen. I cannot find any documentation on how airtight they can make their products. I know that casement as a rule of thumb are pretty air tight, but this doesn’t seem to be easy to reference. How much air tightness difference am I looking at between these windows and some of the more intentional tilt and turn windows?
I have some quotes in process for Zola and Alpen windows as well, but I suspect they will be over budget (international shipping for Zola and Alpen only come in triple “glazing” which I’m not sure I trust the membrane of anyway). Any other brands to look at? Western Colorado for location.
Thanks!
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Replies
First, avoid Jeld-Wen under any circumstance. Doesn't matter what line or style.
Tilt-turns are likely to be the tightest windows, but certainly not the cheapest.
Generally a quality vinyl or fiberglass window is going to be tighter and more energy efficient that wood and a casement is going to be tighter than any sliding style.
Most wood window manufacturers are going to list their air infiltration as less than .3 cfm, which is the minimum acceptable standard, while a high quality vinyl casement should have AI in the .01-.03 cfm range. A vinyl tilt-turn could have AI in the .001 to .005 CFM.
Western CO means you will probably be looking at west coast manufacturers, and while I am not as familiar with west coast folks, I have read and heard good things about Anlin and I have never had problems with Milgard.
It seems the specific air infiltration numbers can be a challenge to easily find from a lot of manufacturers. It seems the less than .3 CFM figure is often reported, but the actual tested number is not reported.
Please revisit your Alpen quote and consider some other factors. Alpen is now offering thin glass as an alternate to the film, which I currently have. I have not had any issues with the film 5+ years out. I have found the air sealing to be excellent as the casement windows have multiple locking points. Air leakage and sound intrusion go hand in hand and while I can't cite a leakage rate I can say that my neighbor came over with his diesel skid steer to plow me out and I didn't even know until I looked out a window.
You mention western Colorado (I live on west slope at 8,000') so be aware that some companies will not deliver windows over certain altitudes with Argon fill. The limit includes passes getting to your location, so think about that. Alpen can and does deliver to high locations. Sierra Pacific, Marvin, and others all had limits that pretty much left Alpen my best option.
Double pane with air, not argon, will put a big hit on your U value despite what the salesmen will try to tell you. Given that window area can be a very significant factor in what should be your whole envelope calculations, going with triple pane and argon filled windows can reduce losses significantly. Mine fixed windows are R6.6, they do better now. The comfort shift is a very welcome bonus, too. Condensation is also hugely reduced. Only my bathroom windows condense and that is due to my preference of steamy showers.
Alpen uses fiberglass framing material which has proven very stable in the brutal sun out here. A previous home I own here has vinyl windows that are pretty much brittle after 15 years. You hopefully will be building and living in the home for a long time, so also consider the downstream savings over time as energy costs are unlikely to go down. Xcel just won a substantial rate increase and I think Black Hills is raising rates too.
Remember that going for R30+ in the walls is money less well spent if you go and poke R3.5 window holes in them. Shifting some wall insulation costs to get higher R windows and better whole wall performance can make for better energy usage. Of course, if the rest of the house is not air sealed to under 1 or 2 ACH (preferably better) then the window leakage is largely moot.
I'm going to push back a little bit, but for discussion purposes. I am a relative amateur.
Roger- thank you for the lengthy reply.
Re: inner film. I'm not worried about 5 years in. I'm worried about 15-20 years in. Still waiting on Alpen quote, I am not discounting it completely, it just seems a source of worry. I'd hate to have condensation build up (I've seen it happen in windows installed 20 years old). Good to know about the glass option. Waiting on quote still from them.
Re: tripple vs double pane. I'm planning a build in Grand Junction. It has a high cooling load in summer, but not extreme heating load in winter. Due to this and other reasons, when energy modeling our house in a passive-house based software, the extra cost from triple pane windows isn't as beneficial for our house as it is in colder climates. It does help, and does reduce the heat pump size by about 25%, but overall energy usage difference is quite minimal. We also have relatively little glass for a custom home.
Greg: Why not Jeld-Wen? Tilt/turn ARE the most airtight, but my question is by how much. Also, our house has small rooms and this style would reduce our interior options so I would like to stay with casement if it doesn't hit our efficiency numbers that much. Not trying to be combative, just trying to fill in the gaps of my question. Good to know about fiberglass, I will push it to the top of the list!
RE: triple vs double pane. I opted for triple pane largely because my design temp is -16F where I live. GJ is milder by far in the winter and much hotter in the summer. Still, the increasingly higher summer temperatures in our area drove my decision to go with the lowest SHGC available. The gain possible during the winter was not worth the gain I would suffer in the summer, especially as I do not have overhangs to protect the windows. Just the same, we do not have AC and use the 30+ degree swings between day and night temps to cool the house overnight and simply close up each morning. All hesitation and worry about lower visible transmission of light have proven baseless. The sun here in Colorado is wicked bright.
The relevance to your situation would be choosing windows to reduce the heat load and thus reduce your cooling needs. Xeriscaping will tend to increase the heat environment around the house, so if you have the option of creating shading with vines on trellises or such, you will find that the load on walls and windows greatly reduced. Don't count on interior shades as the heat load is already inside by the time it gets to the shades. Reflective shades will face the same resistance to getting the heat out of the house as the window presents during the winter months. Block the heat from outside first.
Not sure if the spacer bars in the new thin glass line are different than mine, but the ones in my current windows are much better at controlling the edge losses than the double pane units I left behind in Chicago. Those would ice up at the drop of a hat thanks to the exterior metal cladding which efficiently sucked the heat out of the edges of the window area.