Comment 29155

By g. (anonymous) | Posted February 27, 2009 at 00:33:41

frank,

i am sure you "feel" a difference, qualitatively, however, i'm not suggesting that replacing windows makes no difference to a home's energy usage. i am suggesting that, quantitatively, your heating bill would drop significantly more by addressing some more cost effective but less apparent ways of reducing heat loss in your building.

the thermal gains achieved by replacing windows, i.e. the R value of single vs. double pane windows is minimal.

single pane R value .85
double pane R value 1.5 - 2

marginal gain of 1 or 2 units of thermal resistance

compare this with adding any amount of insulation.

6 inches of fiberglass or mineral batt insulation r value 21
2 inches of extruded polystyrene r value 10

gain of 3-5 units of thermal resistance PER INCH of insulation added

this combined with the fact that the per square foot costs of replacing windows compared with adding insulation are higher by an order of anywhere up to 100 times as expensive while gaining a fraction of the thermal efficiency and it really doesn't make sense to make it a priority

of course what you "feel" is the draft blowing through the gaps in the seals around old windows which can be repaired quite effectively and relatively cheaply compared to replacement.

one is much better off investing in repairing the weather stripping in old windows and doors to seal them properly and investing the rest of the money in insulation. replacing windows should be a last resort especially if you have wood windows. vinyl windows have a very limited life span by design, vinyl breaks down quite rapidly in architectural terms, while wood windows can and do last for centuries with proper care. wood windows can be repaired quite effectively and the end result will be better than any vinyl or aluminum window in the long term.

making energy efficient homes of any age relies on several things, two of which are r value, or the amount of thermal resistance to heat loss through building materials and by air changes per hour, or how well sealed the house is from drafts.

natural resources canada puts out a publication called Whole House Retrofit Techniques which explains all this quite well along with practical advice about solutions to energy inefficient houses.

and just briefly, efficiency ratings on cars are a proven benchmark to the characteristics of a certain vehicles tested capabilities that allow a buyer to understand how different models will perform under similar situations. to state that there is no value to this is completely asinine and barely requires a response. same with energy star ratings. would you say the same thing about horsepower ratings? doesn't it matter how you drive the car and not how big the engine is in terms of how fast you go? so why bother with any specs on anything?

to summarize, i would have to say that actually frank, it is you who are mistaken, but thanks for the opportunity to expand on my point, always appreciated.

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