Your Old Windows, Part 1:
Restore or Replace?
If the craftsmanship and charm of your old windows is quickly being eroded by cold drafts and frost on the panes, it may be time to consider doing something about them. There are two options: restore or replace.
We replace a lot of windows. We probably replace nine old windows for every old window we restore and save. Many windows cannot be restored. Most windows made in the past 60 years or so are not traditional wood windows. The post-war push to build a lot of new housing quickly virtually eliminated the traditional wood window. It took too much time to build and install the window, and required a level of craftsmanship that just was not available. Builders opted for steel and aluminum windows, and factory made, self-contained wood window units that did not need a lot of site preparation and wall modification. Just put them in the opening and nail them up. It was faster, it was cheaper, and builders then, as now, were for anything faster and cheaper. (For more on the post-war housing boom, see Postwar Styles: Cape Cod, Colonial and Ranch.)
But, the sad consequence is that most of the windows installed since the World War are not worth saving even if they could be saved, and most cannot be. Manufacturers that are not out of business don't make those windows any longer, so parts just are not available. If these windows were installed in your house, the only option to fixing your window problems may be to replace the windows.
But, most pre-War housing, and some better housing built since the World War have shop-crafted wood windows. These most often can be saved, and as for parts — if you have a glass company, hardware store and lumber yard in your town, then you have all the parts you are likely to need.
OK, so old windows can be saved, but can they be made as energy efficient as modern windows?
The short answer is "yes". As much as replacement window manufacturers tout the energy saving features of modern windows, research has shown that they are no more energy-efficient than properly restored old windows.
While old wood windows cannot be upgraded to rival the finest (incredibly expensive) super-windows, they can be restored to rival the performance of a more typical (and more affordable) dual-pane thermal replacement window, and usually at a fraction of the cost.
Plus, there are other, nearly as important, advantages of restoring rather than replacing1 you old windows. You not only save on your own heating and cooling costs, which reduces waste and your carbon footprint on the planet, but you also save the resources and energy cost required to manufacture new windows — which considering what new windows are made out of, is not an inconsiderable savings.
You also preserve, not just wonderful old-time workmanship, but the superb old growth wood from which your windows were made. We can't build windows like that any more. It's not that our craftsmen do not have the skill and experience. Any of our master carpenters or cabinetmakers could build a traditional window. But, we can rarely get that dense, heavy old growth wood, and the new wood is … well, we're pretty sure it's wood, but it's not very good window wood.
What Others Say
"A good storm stops air infiltration about as well as most replacement windows, and the up-front costs are much lower. It's like putting money in your pocket."
This Old House
"While the thermal performance of a refurbished single-glazed window fitted with a tight storm can never quite equal that of the best factory-made double-glazed windows, the difference is not so great as to merit the replacement of old windows solely for reasons of improved energy efficiency..."
Renovating Old Houses
"Homeowners tell me they know something is wrong with ripping out all their old windows and throwing them away, but they don't quite know what the alternative might be. They cannot find trades people to do the work.... If you are not a do-it-yourselfer don't worry. More and more savvy trades people are recognizing this new market for traditional window maintenance and repair services …
Save America's Windows
If you own a home with old wood windows, then you are one of those fortunate folks that live in one of the 20 million American houses that do. You are one lucky soul. You have a choice of what to do about your windows that most homeowners do not have. You can restore them or you can replace them with a modern factory-made window. Those who live in houses with steel, aluminum or vinyl windows don't have the choice. These windows cannot be restored. They can only be replaced. Sorry.
Are Replacement Windows a Good Investment
This article takes a look at the case for restoring rather than replacing heritage wood windows. We would like you to consider, just consider, the possibility that your old wood windows can be saved and restored to as good as new and even better than new condition for less money and at a much lower cost to the environment than replacing them. There are advantages to doing so, but also some disadvantages. We look at both and leave it up to you to make up your mind.
The Army-Vermont Study
Before 1996, primarily as a consequence of the pervasive and unceasing marketing of replacement windows after the energy "crisis" of the 1970's, it was nearly universally thought that replacement windows were vastly superior energy performers.
But, in 1996 the State of Vermont and the U.S. Army Cold Regions Research and Engineering Laboratory joined together to actually test the performance of restored heritage wood windows, not by using computer simulations and a laboratory model, but with a field test during actual winter weather conditions2.
Annual Heat Cost Savings
|Assuming your house already has wood windows with storm windows installed, how much would you save each year in heating and cooling costs by replacing your existing window/storm window combination with …||Annual Savings Per Window|
|… new single pane windows with low-E coating and new storm window?||$2.57|
|… new double-pane thermal windows?||($0.37)*|
|… new double-pane thermal windows with low-E coating?||$4.45|
|* This ioption results in higher heating costs.|
The researchers repaired and restored 150 old wood windows all over Vermont, then tested them against replacement windows in similar homes. What they discovered was completely unexpected. They found that …
Well, this was absolutely not the result anyone expected.
The Pentagon is one of the biggest landlords on earth, public or private, owning over 300,000 housing units throughout the world, in every climate you can imagine from the frosty arctic to the torrid tropics, and every point in-between.
This does not include barracks, office buildings, guard shacks, bunkers, hangers, or warehouses, all of which have to be repaired and restored from time to time.
The average military housing unit contains 14 windows. The cost to replace the windows would be about $8,400. The cost to restore the windows, about $2,800. This amounts to a savings of $1.6 billion — which is not chump change even by Pentagon standards.
Everyone had assumed that the thermal replacement windows would be much more efficient than restored windows. The only question to be answered by the study was "how much more efficient".
The last thing anyone expected to find was that restored old wood windows could be just as efficient, and often more efficient, than new thermal windows.
The study concluded that the best outcome resulted from replacing a restored wood window and storm window combination with a low-E coated dual-glazed window. But, even this slight improvement in thermal efficiency resulted in a heating cost savings of only $4.45 per window per year.
Given that any improvement in thermal performance obtained by replacing your old windows with a new double-panel wood window would be very small, if any, is the energy saving worth the substantial cost of replacement windows?
The Haberern Hypothesis
This is precisely the question that researcher, architect and engineer Keith Haberern set out to answer in his study of heating costs in New Jersey. His study results were published in the October, 2007 Old House Journal3 . The study caused quite a stir at the time, and its results are quoted (and misquoted) widely even today.
The Window Wizard Quiz
1. True or False: Windows are the biggest source of heat loss in your house. (ANS)
2. True or False: It is expensive and difficult to repair old windows. (ANS)
3. True or False: Old windows are more difficult to open and close than modern windows. (ANS)
4. True or False: Historic windows are a lead hazard. (ANS)
5. True or False: New replacement windows are more energy efficient than restored original windows. (ANS)
6. True or False: Houses built before 1960 use more energy than newer homes. (ANS)
7. True or False: Replacement windows provide a faster return on investment than repairing and upgrading old windows. (ANS)
8. True or False: Replacement windows will pay for themselves in 5-10 years. (ANS)
9. True or False: Replacement windows are a good value because they require no maintenance. (ANS)
Mr. Haberern concluded that the difference in energy savings between a modern double-pane thermal window and a restored old wood window were insignificant. In fact, an old wood window with a new storm window slightly outperformed a new double-pane window, and was a lot cheaper, with a short 4.5 year pay back period.
How Long to Pay Back Your Replacement Window Investment?
(The Haberern Study)
According to the Haberern study, the most cost-effective window option, with a pay back in 4.5 years, was simply adding a good storm window to the existing single pane window. The worst option is replacing a single-pane window that already has a storm window with a new double-pane thermal window. This option had a pay back of 240 years.
The most interesting finding was that a single pane/storm window combination with a U-value of 0.50 (R-Value=2) slightly outperformed the basic double-pane thermal window with a U-value of 0.58 (R-value = 1.72).
|Cost*||Annual Energy Savings (BTU)||Cost Savings per Window||Pay back Period|
|Add a new storm window to an old single-pane window|
|$50.00||722,218 BTUs||$13.50 per Year||4.5 Years|
|Replace an old single-pane window with a new double-pane thermal window|
|$450.00||625,922 BTUs||$11.07 per Year||40.5 Years|
|Replace an old single-pane window with a new double-pane thermal window with low-E glass|
|$550.00||902,772 BTUs||$15.10 per Year||34.0 Years|
|Replace an old single-pane window/storm window combination with a new double-pane thermal window with low-E glass|
|$550.00||132,407 BTUs||$2.29 per Year||240.00 Years|
|* Costs include installation based on actual costs in New Jersey, including heating costs, at the time of the study.|
The modern window outperformed the restored old window only if a low-E coating was used in the modern window. And, even then, the difference was very small with such meager energy savings that the pay back period was 240 years.
These results almost precisely duplicate the findings of the Army-Vermont study which also found that a restored old wood window with storm outperforms a new double-glazed thermal window, and that only when low-E is added to the thermal window does it very slightly outperform the wood-window + storm-window combination.
The Blasnik Conclusion
Energy consultant Michael Blasnik found similar results in his field study of window performance in New York State using a methodology that could not have been simpler, or more elegant.
He simply checked building permits in his upstate New York community to see which houses had installed replacement thermal windows, then examined utility bills both before and after replacement looking for any change in energy consumption. He found the actual average annual savings from reduced energy consumption per household was $40.00 — not per window — per house.
Based on these findings, Blasnik calculated that it would take, on average, 250 years to recoup the cost of the replacement windows from energy cost savings.4
Reading a Window Label
Windows sold in the U.S. are rated by the National Fenestration Rating Council, an industry-sponsored trade association, and the results of the ratings are shown on a label attached to the window. These ratings are not exactly intuitive, and need a little interpretation.
The "U-factor" or "U-value" is a measure of how much heat is transmitted through the window. The lower the U-factor, the less heat transmitted. U-factor is an archaic measure of heat transfer, and has been replaced in almost everywhere else by the R-value rating. The R-value can be calculated by dividing 1 by the U-factor. In this case, the window's U-factor of .30 translates to an R-value of 1.00/.30 = 3.33. Not much compared to an average insulated wall at R-13.
Windows as Heat Sources, elsewhere on this page.The "Solar Heat Gain Coefficient" (SHGC) measures the amount of radiant heat from the sun admitted through the window. Rated from 0 (no gain) to 1, the rating is best understood as a percentage — simply multiply by 100. This window admits 42% of the solar heat radiation striking it. For more information, see
"Visible transmittance", (VT) as the name suggests is a measure of how much visible light is transmitted through the window. The range is from 0 (none) to 1 (all). Again, it is best understood as a percentage. Multiply the rating by 100. This window is rated to admits 51% of the visible light striking it. No window is rated at 100% since the frame always blocks some light.
Air Leakage" (AL) is an optional test, and many windows do not include it, but if present, is a measurement of how much air leaks through the window in its fully closed position. The rating is in in cubic feet per minute of air flow for 1 square foot of window. The lowest possible rating, indicating the least air loss, is .1, meaning 1/10 of a cubic foot per minute or less. The maximum allowed leakage is .3. The test does not measure air leakage around the window, for example, leakage between the window frame and the surrounding wall, so the actual leakage in your house will likely be greater.
"Condensation Resistance" (CR) is an optional and relatively new test that measures a window's resistance to the formation of condensation. The NFRC describes the test thusly:
"The NFRC Condensation Resistance scale is 1 to 100, with a higher number representing more resistance to the formation of condensation. The Condensation Resistance rating is determined based on outside conditions of approximately -18°C (0°F) with a 6 m/s (15 mph) wind, and inside conditions of approximately 21°C (70°F) with relative humidities of 30%, 50%, and 70% taken into consideration. The Condensation Resistance rating is a value that considers the relative area under condensation at these three humidity levels, which are then normalized, and the degree to which the surface temperatures are below the dew point for the frame and for the glazing are taken into account. The Condensation Resistance rating specified in the NFRC rating is based on the lower of the frame, center-of-glazing, or edge-of-glazing values."More simply: The range is from 1 to 100, with a higher number indicating a higher resistance to condensation. The problem with the measure is that it is hard for the typical window buyer who may not have an advanced degree in thermodynamics to translate the result to the real world. A lot depends on the average humidity level in your house, and if you install new windows, the average humidity level is likely to rise because you have probably sealed a lot of old air leaks. So the risk of condensation also rises. Bummer, dude!
Generally, however, you should avoid windows with a CR rating of less than 50. The window CR rating here barely makes the cut. A high-rated CR is less likely to condensate, but not guaranteed against condensation. Any window will show condensation under the right conditions. If the CR is not shown, you should probably avoid the window. If the CR rating was high, the manufacturers would brag about it.
The Hill Study
An earlier study by William Hill at Indiana State University, which attracted little notice at the time,5. found much the same result.
His 1990 study looked at actual window performance in the field rather than in the laboratory and concluded that merely replacing old windows, without any other energy improvement in the home, results in an annual savings in energy costs of just 1.4% per year.
He did not bother to translate this into dollars, but we did. In our town, Lincoln, Nebraska, this would amount to an annual savings of $33.12 for an typical home which is what you would save replacing 10 incandescent light bulbs with compact fluorescent bulbs at a cost of about $15.00, whereas replacement windows with installation would cost $10,000 (at least) to produce the same savings.
It would take about 311 years to repay the costs of replacement windows from energy savings alone. Of, course, this is using our local, Lincoln, Nebraska, rates for electricity and natural gas — some of the lowest in the country. So, it might take as little as 200 years where you live.
National Trust for Historic Preservation
A national study published in October, 2012, funded by the National Trust for Historic Preservation, looked at various retrofit measures used to restore and enhance old windows and compared them to new replacement windows in five cities, representing distinct climate conditions across the U.S.
The study concluded that old windows restored using commonly available materials and processes easily exceed the energy performance of typical replacement windows and can be nearly as effective as very expensive high-performance replacement windows, at a fraction of the cost of new windows.
The study's authors concluded that …
… options that retain and retrofit existing windows are the most cost effective way to achieve these energy savings and to lower a home’s carbon footprint… Almost every [window] retrofit option offers a better return on investment than replacement windows… In cold climates, all other retrofit measures … offer a higher average return on investment when compared to new, efficient replacement windows. In hot climates, all of the study's retrofit measures offer a better average return on investment than new windows…
To read the full study report, download "Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement".
Lies, Damn Lies & Computer Models
All of these studies have something in common:
- They were done by researchers who have no connection to the window industry, and have, therefore, no interest in selling you any replacement windows.
- Not a single one of these independent studies found any evidence of substantial energy savings from replacing old wood windows — especially restored wood windows — with modern thermal windows.
- The studies in which the payback period was calculated found a striking similarity in payback periods. They found a payback of well over 200 years, which is more than four lifetimes of even the best replacement windows
So, where is the big savings on my heating bill everybody keeps talking about? We've all seen the ads in magazines and on television:
"Save 35%, 40%, even more on your heating bill. Replace your old, tired wood windows with our new Magnifico plastic windows!"
How can replacement window manufacturers claim such huge energy savings? Are they just lying?
Not really (well, maybe just a little).
First, in defense of window manufacturers, no reputable manufacturer makes such claims, and those companies that do are usually out of business pretty quickly. Unfortunately, however, local retailers often do make very exaggerated claims, as evidenced, for example, by a recent advertisement we found on the web from the Home Depot (shown below).
Second, window manufacturers don't do actual field testing of their windows. They rely almost entirely on computer models or simulations and laboratory testing.
Computer analysis is used to build mathematical models of the various window components and then calculate the window's resistance to heat transfer. Then, a physical test is carried out in a laboratory to confirm the model. The laboratory testing environment, the "hotbox", is very artificial. It bears almost no resemblance to the actual environment of your house. This artificiality skews the computer models, making them inaccurate. Heat is not actually lost the way the computer simulations assume it is.
At no time is the window actually installed in a house and the results evaluated, so the computer models themselves are rarely compared to the real world experience of windows installed in a home. But, when they are, they are found to be very inaccurate. The Earth Advantage Energy Performance Score Pilot Project for the Energy Trust of Oregon published in 2009 found that the most commonly used energy models were wrong as much as 96.6% of the time, regularly overstating energy savings.
The problem is that the most commonly used model does not accurately reflect how heat is actually lost through a window. To understand why it is wrong, we need to take a look at the many ways heat moves and how the complexity of heat movement through windows affects the testing and rating of windows in the laboratory which, just coincidently, are the subjects of the next section: Testing & Rating Windows.
1. Sedovic, W. and J. H. Gotthelf, "What Replacement Windows Can’t Replace: The Real Cost of Removing Historic Windows" ( Journal of Preservation Technology, Vol. 36, Number 4, pp25-29, 2005. (Download PDF)
2. James, B.; Shapiro, A.; Landers, S. and D. Hamenway, "Testing Energy Performance of Wood Windows in Cold Climates", (1996.) University of Vermont, U.S. Army Cold Regions Research and Engineering Laboratory. (Download PDF))
3. Keith Haberern as quoted in Noelle Lord, "Embracing Energy Efficiency" The Old House Journal pp 40-45, Oct, 2007.
4. Blasnik, Michael quoted in R. Yagid, "Should Your Old Wood Windows be Saved", Fine Homebuilding, Issue 210, March 11, 2010. (Download PDF)
5. Hill, William W., "Replacement Windows and Furnaces in the Heartland: Indiana's Energy Conservation Financial Assistance Program", Center for Energy Research, Ball State University, Indiana, 1990. (Download PDF)