So we're building a new home and investing in the tightest envelope we can afford - ICF walls, spray foam insulation, under slab insulation, etc and naturally presumed we should also buy the best windows we could afford.  However, we had an energy analysis done and by going from a moderately priced U-0.28 fiberglass window to the much more expensive Serious 725 series with a U-factor of 0.18, we saved a predicted grand total of $9 month on a total predicted bill of $190/month.  It also did not decrease the size of the HVAC equipment we required.  Can this be true??  The engineers explanation was that the relatively modest improvement in R-value provided by the Serious windows and the relatively low proportion of surface area of windows to the other planes of the house that lose/gain heat (ie roof, walls, slab, etc) explained the modest improvement in performance.  With the Serious windows being 50% more that the U-0.28 windows, the payback (not necessarily the only consideration) would be enormously long, if this is true.  Does anyone have any ideas or thoughts?  Thanks in advance for any help.

Posted By NOVA on 10 Feb 2010 12:13 PM

 So we're building a new home and investing in the tightest envelope we can afford - ICF walls, spray foam insulation, under slab insulation, etc and naturally presumed we should also buy the best windows we could afford.  However, we had an energy analysis done and by going from a moderately priced U-0.28 fiberglass window to the much more expensive Serious 725 series with a U-factor of 0.18, we saved a predicted grand total of $9 month on a total predicted bill of $190/month.  It also did not decrease the size of the HVAC equipment we required.  Can this be true??  The engineers explanation was that the relatively modest improvement in R-value provided by the Serious windows and the relatively low proportion of surface area of windows to the other planes of the house that lose/gain heat (ie roof, walls, slab, etc) explained the modest improvement in performance.  With the Serious windows being 50% more that the U-0.28 windows, the payback (not necessarily the only consideration) would be enormously long, if this is true.  Does anyone have any ideas or thoughts?  Thanks in advance for any help.

If you look at some of my other posts, I'm in the same boat.  I've all but ruled out the Serious windows because we'd have to sacrifice too many other things to get them.  Interestingly, we are doing many of the same things you're describing (minus ICF walls). 

What I've found in my research is that there are some windows that offer similar performance for less money, but they are vinyl rather than fiberglass.  How important are fiberglass frames to you?

Posted By Lee Dodge on 10 Feb 2010 03:41 PM
Are you in a location that can take advantage of passive solar through windows on the south side? I looked at Serious windows, but found that I could do much better with higher solar gain windows that were somewhat higher in U-factor, and were also less expensive. To quanitfy results, I used ResFen, the free software from Lawrence Berkeley - Dept. of Energy. Too much focus on U-factor and too little on solar gain might be shortsighted unless you are living in the clouds.

I'm curious if anyone else has used this tool?  I hadn't used it before but downloaded just now & ran with the specs for the house we're building.  It gave me an annual cost to heat/cool of $270.  That would be fantastic, but it's I don't know if I believe it.  A little over $20/month to heat/cool a 2000 sq foot house?
 

Posted By toddm on 11 Feb 2010 08:58 AM

Consumer Reports liked Andersen for value and performance among the major brands. alside, an inexpensive vinyl window, also did well.