I just had another window salesman knock on my door and tell me that switching out my windows can save me 40% to 50% on my energy bills. When I pressed him, he said that's for switching out metal double pane windows with his high efficiency triple pane ones here in Texas. He promised much higher savings when it comes to switching out my single pane metal ones.
I've modeled a lot of buildings for the Weatherization Assistance Program using the NEAT tool and windows have never ranked. Even Krigger and Dorsi say that windows have a long pay back period and are probably the last things you should do.
I have this conversation all the time with my wealthier client base. They always seem to have tight, double paned windows and want to switch them out before doing any air sealing or insulation. I end up talking them down. And it seems like the windows guys have an evangelical zeal to convert energy auditors to their way of thinking.
I'd like to see the research. Do you know of any studies on switching out windows? I'm specifically looking for switching out double paned metal windows that are fairly tight.
If you look closely at the inputs for Manual J in Wrightsoft; exterior storm windows provide some benefit.
Example: single glaze wood
SHCG w/o storm 0.64
SHCG w/storm 0.56
U-val w/o storm 0.90
U-val w/storm 0.57
Example: double glaze wood
SHCG w/o storm 0.56
SHCG w/storm 0.51
U-val w/o storm 0.57
U-val w/storm 0.44
Actually the larger air gap can create convection loops, so not necessarily a benefit. Exterior storms are also designed to be sealed on three sides with an allowance for weeping/condensation/drainage on the lower edge.
Without first hand experience, interior storm windows seem to be a better option.
Surely not true. The bigger spacing allows for more convection and convective losses between the two surfaces.
I certainly agree with most of the posts in reply, with one additional thought.
Determine the cause of the reasoning. I have found in some cases that the homeowner is really talking about one or two specific rooms and has then made the mental leap to all rooms. For instance a bedroom on the north side that is coldish in the winter time, or a favorite sitting room for sedentary activies such as reading. In these particular cases, it may be perfectly reasonable to swap out the glass for super triple glazing and achieve the comfort level the customer desires because of radiation effects. Hot (the customer) to fairly cold (the window).
You know, the sort of thing that was happening when your grandmother still complained of drafts in her house that she had heated to stifling temperatures.
Window salespeople have 'see and feel' going for them:
See- new windows look much nicer than an airsealed attic and basement
Feel - customers will feel less intense convective loops and radiant losses replacing a R-1 single pane with a R-3 double pane.
Customers' 5 senses are hard to argue with! And who actually verifies energy savings anyway?
That is a loaded question, and depends a lot on the window to wall ratio of your windows. I just was in a webinar today which spoke of dense-packed insulation, the fact that many older homes have wall cavities which are open into the attic, etc. I looked at windows for my house, but one issue which has kept me away is that I would have to have a larger opening cut for current egress requirements as part of changing out our bedroom window, so add that to all the other costs. I have metal double-panes currently. I can think of a number of air sealing, insulation and radiant barrier tacks to take before looking at windows again.
We've done audits and upfits to several thousands homes in South Carolina over the past four years. Our customers are interested in lower power bills and are generally on a limited budget. The cost vs. benefit of insulation, air sealing, duct sealing, or even a high efficiency HVAC replacement as compared to replacement windows seems like a no-brainer. In only a couple of cases out of thousands did replacement windows make any economic sense. www.carolinages.com
I think the appeal of replacing windows is largely on the aesthetics for most homeowners. Nobody wants an ugly, old rattling window.
The cost savings are there as well, especially for homeowners in the north that have to endure brutal winters. We've seen many customers that have lowered their energy bills, myself included.
We've also written quite a few articles and guides about energy-efficient windows and energy savings on our blog over at http://www.feldcochicago.com/ . Check it out sometime.