Are high performance windows worth it?
We’re in the final stages of planning a new house that we hope to build this summer. We have just met with our contractor who has prepared an estimate. Our builiding criteria includes R45 walls, R65 roof, R20 slab, lower than 1 ACH at 50 pascals, and windows with a u value of at most .2. Our contractor is ready to meet our specs, but he told us that he’s not convinced that our window spec. is worth the expense. All along, I’ve felt that one of the high-performance Canadian windows would be critical to the performance of our house. But since today’s meeting, I’ve been playing with a heat load calculator mostly to make sure that we’ll be able to heat the house with a minimal system. When plugging the above specs into the system, we need 20k btu’s for our heating system requirements. I was amazed to find that if I reduce the R value of our windows (we have planned for about 375 sq. ft. of window total) from 5 to 3, the heating system requirements go from 20k btu to 22,250– a little over our goal, but not by much… and I’m assuming that there is a big savings up front by doing this. The annual heating costs (assuming propane at $2.50 a gal., although we are actually likely use a mini-split or a pellet stove) go up by $150 a year (from $650 to $800) with the lower grade windows. I’m assuming that the cost difference between these windows would be several thousand. This is making me question the wisdom of the good windows. Can anyone tell me what I’m missing in all of this, orr is there a little too much hype surrounding the “good” windows?