We have had a recent cold snap and this puts the inefficiency of single-pane windows on display.
Arriving at the house, built 1973 with all its original windows, the temperature was 15F. It had gotten down to about 7F during the night.
This is what the windows looked like from outdoors.
Every single window was icy.
Single-pane windows contain 1/8" thick glass and have an R-value (insulation resistance) of between .5 and 1.
Typical wall insulation, by comparison, is R-13.
In addition, since these are older windows, they do not fit tightly and so there are gaps all around and between the moving sashes. Moving air can be felt at every window.
This is inefficiency on parade!
Heat moves toward cold. In the winter heat is escaping each window opening. In the summer heat is trying to enter each window opening.
A house's energy efficiency breaks down to percentages - approximately 30% walls, 30% windows/doors, 30% attic insulation and upper-level lights, and 10% wall openings (like receptacles and switches). That 10% increases if there is a fireplace. A crawl space changes all that too. And the direction the house faces.
If you add up the area of all the windows and doors in this house the area adds up to about the equivalent of three exterior bedroom walls with R-1 or less! That represents huge energy losses!
The house is vacant so the heat was not turned up very high. As we increased the heat the ice inside the windows began to melt. This created puddles here and there, which rested on wood surfaces, and on wood windows water is not a good thing!
Adding storm windows can increase the window insulation to between R-3 and R-4. Storm windows are a cheaper alternative to replacement windows.
Newer double-pane windows with a 1/4" gap between the panes increases the insulation to about R-2. If there is a 3/4" gap between the panes the R-value is bumped to between R-2 and R-3. A good low-E coating on the inside of the two panes increases the R-value to between R-3 and R-4 and adds heat protection, depending on the quality of the window. Really good replacement windows boast R-values of R-6 to R-9, but they don't come cheap!
If/when you buy replacement windows, look for the U-factor ratings. If the number 1 is divided by the U-factor you arrive at the R-value. So a lower U-factor is the higher the R-value. In Virginia the Energy Star standard for new windows is a U-factor of .32 or less. The low-E coating provides sun/UV/heat protection, called the Solar Heat Gain Coefficient (SHGC).
My recommendation: one of the most common upgrades to older homes is to replace the windows. This not only gives the house more energy efficiency (despite what the commercials say, cost break evens are variable, if ever obtainable) but the new windows work! They don't stick or act like guillotines! Cheaper than new windows, if the old ones still work well, is the installation of storm windows. They add great efficiency more cheaply, and work too!
Jay Markanich Real Estate Inspections, LLC 
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560
Good morning, Jay.... that reminds me of homes with metal framed windows in New England... those are made for a warm climate...moisture and ice build up on the wood window sill.....then it becomes rotted....
The metal causes heat conduction Barbara. Covection is to, conduction is through.
Please remind me, which one is the 12 year old? They are both the same size.
Jay, the normal buyer pays no attention to insulation, windows and energy conservation! And they pay dearly for it! Enjoy your day!
It's cold enough outside we don't need a airflow from faulty windows. Think I just may hibernate today.
They pay attention once I am done with a home inspection Wayne!
It's not as cold here today as the past couple James, but still cold!
I did an addition on my 1970's cabin - new space has foam insulation and Pella windows. Old space at least got wrapped with insulation when we replaced the siding with hardi board, but funds ran short before we could replace the windows. At least I have storms. You can tell the difference!
People don't realize how much comfort, and efficiency, storm windows can deliver Jeanne. And it's much cheaper than replacement windows.
Hardi-plank was a great addition also. Good thinking.
Great advice on those windows and certainly needed at this time of year. It is soooo cold outside.
It gets cold there Debbie?
The post is somewhat of a tutorial. Do you have good windows in your building? If not, why not?
I can't recall seeing single pane windows in a zillion years...but here...you would be paying mega bucks for heat.....and probably still freezing !
Good morning Jay,
Depending on the window and conditions there are some unusual designs just like spider webs!
Make yourself a great day.
It doesn't take a Rhodes Scholar to figure that single pane windows are not energy efficient.
What's so surprising is the "thermal" double pane windows that aren't much better.
S&D - ay ay Cap'n.
Raymond - unusual to be sure, but I still see this a lot.
Lenn - but new windows work better!
Jay, I have a saying the most energy efficient window out there is the one that is not there
.
Wow who has a R-6 to R-9 window?
Most excellent posting and subject matter....Keep up the good work and thank U
Meester Dohn - I have heard radio ads by local companies. One window rep I did an inspection for said his windows were R-10! While I didn't believe him, I was not going to argue on a home inspection!
I have seen windows in custom new homes with U-factors of .15.
Richie - thanks! Did you mean to say, "thank U-factor...?"
; >)
My daughter bought a new old house this summer, and yesterday I was at her house and noticed all her storm screens were still down. 14 windows in all were freezing her out. Good thing her Dad is a home inspector and notices stuff like that. She called last night and said how much warmer her house was. Bingo.
Jay Markanich ... the windows in our "newer" home are not the best. Add on top of that issue, we are built upon a high water table. The result is that we get wet windows way too often, even with a de-humidifier going in the middle of window. I like the idea of the storm windows .. at least until we tackle the remodeling we have in mind. Thanks for the little push and great idea!
Gene
I haven't had single pane windows in a million years. If I still had them, I would feel the "pain" in my wallet when I looked at my utility bill. Thank goodness for storm windows.
Great advice! We're looking to replace the windows are on our house, which are double paned but are old and have failed. Thank goodness for thick curtains! Thanks for posting!
Heat loss, moisture, mold blackening the bottom with the wetness. Triple glazed and high performance windows and what the heck. Add some roman insulated shades to lower and seal up at night. Makes the place warm, toasty and money to show up. Left over from down the drain of wasted heating costs.
I grew up in a house that had jalousie type windows, my dad used to remove the screens every winter and wrap them in visquene and put them back up to keep drafts from blowing in...lol, I think you call that -R value!
Hi Jay, it is well worth the investment for homeowners to put in new windows. Thanks for sharing.
I bet you are just a picky a fellow when you work for home buyers Scott. I got a call today from a friend who put in what the HVAC company called a "terrific" new heat pump. She said her small house (1500 sq ft) doesn't get warmer than 59F. I asked her to read me the numbers on the plaque. It's a 5 ton unit! Ummm...
Gene - I'm hearing builder grade! But storms may help you, but I say that not knowing what kind of windows you have.
Joel - I would have believed you if you had said 500,000, but really, a million?
Laura - thick curtains help! And the double-cell shades.
Andrew - all that ought to work even in Maine!
Our rear addition had jalousie windows too Fred. They were not at all efficient. But still, we didn't wrap the screens. Instead of R-value, don't you mean W- value? You know, Wrap- value.
Sybil - agreeing with you that comfort is worth what it takes, but it's not exactly a $ investment! Still, would I want new windows? Yes.
It's amazing what new windows can do to keep the house warm. And the utility bill down.
That's probably true Kevin, depending on what is being replaced. The cheapest form of energy improvement would be? Caulking.
Fortunately, storm windows look pretty good these days versus the old steel looking ones. Anodized frames can look good from the street. I use storm windows on my older rental properties so that I don't deal with lost seals on doubles.
Joe - when I was first married (1977) we rented a townhouse and I suggested that the owner put on storm windows. They were the color of the trim and looked pretty good. I drove by the place the other day and they were still there!
We have new windows and they leak air in the center where they raise up and down. Dont know if they put them in wrong or what. These are expensive ones too.
Ricki - they may be missing the thin, hairy strip that goes in there. Lift the lower sash up and look to see if there is an air block of some sort in there. If the block is there and it is leaking then it's the window.
Good info; I was not up to spped on the R factor and calcs. Understand them much better now. And glad we have newer double-paned windows. Doors are our problem with air leaks.
Mel
They are as important as windows Mel. But sometimes air flow is easier to block.
Jay, I can't find any windows that claim higher than r-5 and they are hecka expensive. I am doing a post on getting away from insulated glass windows all together
Jay Markanich I have seem some posts that mentioned double pane windows can have the seal broken hence not so effective or energy efficient. So which is better? (Of course your post has the answer - however, wondering.....)
You have too much time on your hands Charlie! I can't remember brands off the top of my head, but I have seen U-factors as low as .15. I just quick went to Andersen and their best is .26.
Personally I think storm windows are the way to go. And I look forward to your blog!
Praful - I had a blog just last November on broken seals. Over time any double-pane window that is gas filled can cloud up from broken seals.
http://activerain.com/blogsview/4543558/what-do-i-do-about-broken-window-seals-
The broken seal does not affect the efficiency that much.
U factors are one thing, and R-value is another---not directly related to each other.
I don't know Charlie, I thought they were. Dividing the U-factor into 1 gives you the other!
http://pressroom.pella.com/fast_facts/153/confused-about-rvalues-and-other-window-and-door-terms
Pella uses them interchangeably.
Maybe I misunderstand what you mean.
Great post Jay!
Being from the warmer coast, I have a question. What is a storm window?
It is the smaller version of a storm door Tom. Do you have those?
Think more square.
; >)
Did some quick Googling, it looks like a window install over the existing window, much like a storm door Jay. this is new to me Jay; I must live a sheltered life. :)
I can see how this would be less expensive than replacing the windows.
Tom - I thought you were joking! I'm sorry! I gave you back a flip answer!
In warm climates storm windows might be cumbersome, but still effective toward insulating windows during the AC season.
Funny, when I was in South America I ran into a Canadian who had never heard of M&Ms! I thought he was kidding! He wasn't...
had to come back to this Jay Markanich ...since i have some Andersen 20 year insulated windows that frost a bit in the subzero weather...I'm wondering whether that means i need to replace soon...
No problem Jay.
Maybe Canadians have a different alphabet eh?
If they are 20 years old, Ginny, they may not have the current ability they once had, but I have NO experience with sub zero temperatures so I don't know.
Well, Tom, hopefully they call them J&Js there?