Your Old Windows: Restore or Replace?

Where an old wood window is restored and equipped with a good storm window, it has been repeatedly shown in field studies to perform at least as well as a typical thermal replacement window — and at a lower cost to the environment as well as to your wallet.

If the craftsmanship and charm of your old windows are 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.

Unfortunately, many windows cannot be saved.

Windows made in the past 70 years or so are not traditional wood windows.

The post-war push to build a lot of affordable housing as quickly as possible virtually eliminated the traditional wood window. It took too much time to build, even more time to install, and required a level of craftsmanship that just was not available at the scale needed to build over 5,000 houses a day. [1]

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.

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.

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 of the 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 will ever need.

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.

Energy Efficiency

What Others Say

Tom Silva "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."

Tom Silva
General Contractor
This Old House

"While the thermal performance of a refurbished single-glazed window Renovating Old Houses Cover fitted with a tight storm can never quite equal that of the very 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..."

George Nash
Renovating Old Houses

"Homeowners tell me they know something is wrong with ripping out all their Save American's Windows cover 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 &hellip 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 …

John Leeke
Save America's Windows

While old wood windows cannot be upgraded to rival the finest (and incredibly expensive) Ger­man or Can­a­di­an 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.

Other important benefits also flow from restoring rather than replacing [2] your 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.

The environmental carbon cost of your old windows has already been paid, many decades ago and does not have to be paid again.

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 anymore.

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 find that dense, heavy old-growth, straight-grained wood. The new wood is … well, we're pretty sure it's wood, but it's not very good window wood.

Why Does the Army Care About Windows?

The Pentagon is one of the biggest landlords on earth 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 latitude 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 (MHU) 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.

If you own a home with old wood windows, then you are one of those fortunate folks who 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 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 know you have been bombarded by window manufacturers with advertising suggesting that not only are replacement windows more energy efficient, but due to the climate crisis, it's almost un-American not to replace your old windows with their new super-duper high-efficiency dual pane, argon-filled, low-E coated windows.

For years we never even thought to look into the idea that the propaganda might not be true. When we did, we discovered that the claims were largely baseless.

We had been fooled. But, in our defense, so was nearly everyone else.

We are going to lay out the evidence for restoring rather than replacing old wood windows. You can accept it or not. It's entirely up to you.

But, we ask 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 1970s, 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 (CRREL) 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 conditions [3] Somethat that had never been done before.

Army-Vermont Study:
Annual Heating Cost Savings
If your house already has restored 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 Heating and Cooling Cost Savings Per Window
Option 1: New single-pane windows with low-E coating and new storm window. $2.57
Option 2: New double-pane thermal windows? –$0.37*
Option 3: New double-pane thermal windows with low-E coating? $4.45
* Option 3 rulted 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 …

Not the result anyone expected.

Everyone had assumed that the thermal replacement windows would be much more efficient than restored windows. The 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 even 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 option resulted in only a slight heating cost savings of $4.45 per window per year.

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 payback 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 payback 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 Pay­back Per­iod (Yrs)
Add a new storm window to an old single-pane window
$50.00 722,218 $13.50 4.5
Replace an old single-pane window with a new double-pane thermal window with low-E glass
$550.00 902,772 $15.10 34.0
Replace an old single-pane window with a new double-pane thermal window
$450.00 625,922 $11.07 40.5
Replace an old single-pane window/storm window combination with a new double-pane thermal window with low-E glass
$550.00 132,407 $2.29 240.00
* Costs include installation based on actual costs in New Jersey, including heating costs, at the time of the study.

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 $1,200 average cost ofa replacement window?

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 Journal [4]. The study caused quite a stir at the time, and its results are quoted (and misquoted) widely even today.

Mr. Haberern concluded that the difference in energy savings between a modern double-pane thermal window and a restored old wood window was insignificant.

In fact,

[A]n old wood window with a new storm window outperformed a new double-pane window, and was a lot cheaper, with a short 4.5-year payback period.

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 payback 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 Verdict

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[5]

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.

A  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. It has been replaced 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 .48 translates to an R-value of 1.00/.48 = 2.1. Not much compared to now minimum for an insulated wall of R-19.

B  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. A window rated 1 admits 100% of the radiant heat striking the outside of the window. This window admits 42% of the solar heat radiation striking it. For more information, see Windows as Heat Sources, elsewhere on this page.

The admission of as much solar radiation as possible in winter is desirable, so in net-heating climates, high SHGCs are better. In net cooling climates, like most of the U.S. South and Southwest, a low SHGC is desirable.

CVisible 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 admits 51% of the visible light striking it. No window is rated at 100% since the frame always blocks some light.

DAir Leakage (AL) is an optional test, and many windows do not include it. If present, is a measurement of how much air leaks through the window in its fully closed position. The rating is in cubic feet per minute of airflow 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.

ECondensation Resistance (CR) is an optional and relatively new test that measures a window's resistance to the formation of condensation.

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 increase because you have probably sealed a lot of old air leaks. So the risk of condensation also rises.

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 is not guaranteed against condensation. Any window will show condensation under the right conditions.

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.

The Hill Study

An earlier study by William Hill at Indiana State University, which attracted little notice at the time, [6]. found much the same result.

The Window Wizard Quiz

Are you a Window Whiz or a Win­dow Wuss? Here's your chance to test your Win­dow Wis­dom.

1. True or False: Windows are the biggest source of heat loss in your house. (Answer)

2. True or False: It is expensive and difficult to repair old windows. (Answer)

3. True or False: Old windows are more difficult to open and close than modern windows. (Answer)

4. True or False: Historic windows are a lead hazard. (Answer)

5. True or False: New replacement windows are more energy efficient than restored original windows. (Answer)

6. True or False: Houses built before 1960 use more energy than newer homes. (Answer)

7. True or False: Replacement windows provide a faster return on investment than repairing and upgrading old windows. (Answer)

8. True or False: Replacement windows will pay for themselves in 5-10 years. (Answer)

9. True or False: Replacement windows are a good value because they require no maintenance. (Answer)

Adapted from an article appearing in Old House Journal, June 2016.

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, the annual savings would be $33.12 for a typical home.

You save more by replacing 10 incandescent light bulbs with LED bulbs at a cost of less than $8.00 per bulb, whereas a replacement window with installation would cost an average of $1,200 to produce the same savings.

It would take about 362 years to repay the costs of the window from energy savings alone.

Of, course, this is using our local 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 …

[O]ptions 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 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 National Trust 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:

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 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 statements. It is now illegal to do so.

They may hint at substantial energy savings, but no longer make outright claims since the Fed­er­al Trade Comm­mis­sion challenged such "exaggerated and unsupported" claims in a lawsuit against five window companies for "deceptive trade practives" in 2012. The FTC has warned of additional lawsuits for energy savings claims not backed by scientific evidence.

Unfortunately, however, it took a while for some window sellers to get the word. As late as 215, for example, Home De­pot was still advertising grossly exaggerated energy savings of its very average replacement windows.

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 installed in an actual 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 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. Post-war Housing Styles Cape Cod, Colonial, and Ranch.

2. 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)

3. 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))

4. Keith Haberern as quoted in Noelle Lord, "Embracing Energy Efficiency" The Old House Journal pp 40-45, Oct 2007.

5. Blasnik, Michael quoted in R. Yagid, "Should Your Old Wood Windows be Saved", Fine Homebuilding, Issue 210, March 11, 2010. (Download PDF)

6. 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)


Rev. 06/20/23