Posted By strategery on 02 Jul 2012 03:15 AM
Some more questions-
So a triple pane window argon filled is *probably* and R-5?
Given that the wall around that window is about R-12 - R-15, that glass is ALWAYS going to be a weak spot where the conductive heat loss occurs, correct?
I know in passive solar designs, they try to limit windows on the north side for 2 reasons: 1) glass on the north side receives little to no direct sunlight and therefore no beneficial solar gain during the winter 2) the glass is a weak spot of the wall and is susceptible to greater conductive energy loss
I really only will have one opportunity to get these two windows right when making this replacement. Should I go for the very best window I can afford for these two north-facers? or is it not that big of a deal as long as it's a double pane low-e with good air-sealing?
Most good triple pane windows will be in the R-5 through R-7
range, although Serious Windows makes a dual pane window with R-5 through R-9 (very expensive). They way they get these values with dual pane is by utilizing heat mirror technology. Some people question the longevity of this technology but from what I read it is reliable. Although European manufacturers find this technology flawed and don't use it, they stick with triple pane.
R-Value is only ONE part of the equation. Windows must also be AIR TIGHT. A leaky window in winter will let in the cold and let out the warm interior air. The reverse is true in summer. The other part of the equation is SOLAR GAIN. If you are in a heating dominated climate, having a lot of south facing windows that have a high SHGC will help heat your home during winter. Even though at night the windows have a negative impact on the home, the overall SHG makes up for it as it cuts your heating costs during the day.
Windows also serve the function of letting in natural daylight and venting the home (if operable). North windows SHOULD be minimized but not eliminated as they provide indirect light during the daytime. Nobody wants to live in a cave, let me clarify that, most people don't want to live in dark caves.
Your question has a lot of factors. How long do you plan on living in the home? I would get pricing for each design (dual and triple pane), check the air sealing ratings, and then make a choice based on your budget and goals. Either way, you are looking at a long term ROI.