Heritage Restoration, Inc.

Saving Old Windows Is Green and Efficient

Each year our houses get a bit older; parts continue to wear, fall off or just stop functioning all together. A house has parts meant to protect and parts meant to operate.  Windows, especially ones over 100 years old, operate poorly and become drafty.  There is a fine line between functioning well and struggling, where parts operate one week and stick another.  The New England climate doesn’t help much.  We can be soaking wet, hot, dry, and cold with a mountain of snow and ice.  Years ago, lead paint provided the protection against our harsh environment.  It is not easy to find a happy medium, but hundreds of years of practice and the right methods and materials can certainly make it possible.


The American perception of building stewardship has been sold out.

Houses and buildings are much more complex than the industry leads you to believe.  But they are really simple to maintain when you look at the parts, it’s just not “sold” to you that way. The days of buying parts and fixing things are long gone.  When was the last time you resoled a shoe?  Or how about fixed your TV? It is easier to sell a package that is disposable than to teach you how or give you the parts to fix it.  Oh, and you can buy it again and again, which is the manufacturer’s goal.


Windows have a bad wrap.  The need for window replacement is often misdiagnosed.  You can be easily sold something that will make little difference.


Breaking The Window Myth

  • 30% of replacement windows are less than 10 years old.
  • Heat passes through glass 10-12 times faster than through walls
  • R-Value measures the insulating value of a window, not the entire system. While a U-Value is how well a window keeps heat inside a building, including the whole window system.  What good is the rating when the windows are improperly installed?
  • Single-thickness glass is rated less than R-1.0.  A storm window is about R-2. Double-glazing with a sealed air space is approximately R-2.0. Double-glazing using an inert gas and Low-E coating, a film that blocks heat from entering in summer and escaping in winter, is rated from about R-3.0 to R-4.5.  http://www.e-star.com/ecalcs/table_rvalues.html
  • Storm windows reduce airflow, reducing heat loss.  You can apply a Low-E coating on the glass to minimize heat transfer.
  • http://www.nfrc.org/ is the web site for the National Fenestration Rating Council


There are simple ways to figure out what is going on.  Why? They are the easiest building part to replace.  But are they the source main heat loss?  Here are some things to do:

  • Blower door test and energy audit.  A blower door test pressurizes a house to reveal airflow through cracks.  An energy auditor also analyzes your annual heating consumption and forecasts you potential savings based on their recommendations.  We have observed blower door tests reveal bigger issues than windows, where major savings can be made by closing gaps and reducing other points of air flow.
  • Infrared scanning.  During a blower door test, or when the temperature difference is at least 15 degrees different.
  • Fit and operation assessment.  Sometimes a refit or tune up can make windows more efficient and functional.
  • Storm windows.  There are numerous studies supporting the use of storm windows to increase your window’s efficiency.  Sometimes more than 4 times the efficiency of a single pane window.
  • Weather strip existing windows.  There are numerous options.  Stay away from adhesive or foam types, they tend to wear quickly.  Some of the best types require a groove to be cut into the sash, and should be done by a professional.  Stuff gaps with baker rod once you close in for the winter.
  • Close your storms and lock the windows.  That makes a big difference in efficiency.



Replacing Single Pane Glass

Single pane window glass is easily replaced.  Double glazed glass is very difficult, if not impractical to replace.  Typically the entire double glazed sash is replaced, not just the glass.  Single pane glass is about $2.00 per square foot, where double paned glass can be upwards of $25 per square foot. Single pane glass is held in with glazing putty.  Most of the time, it can be removed easily.  So how do you replace glass?


  1. Heat gun
  2. Pull Scraper and push scraper, like a 5 and 1
  3. 6” drywall knife
  4. Glazing knife
  5. Glazing Putty
  6. Glass
  7. Shellac, Boiled Linseed Oil, or Quick Dry Primer
  8. Paint


  • Heat- The glaze gets soft at about 500 degrees.  You can use a heat gun, but the high temp can break the glass.  Use a metal drywall knife to defect the heat from the glass.
  • Or Break the Glass- You can also set the window on a table with the outside down.  Place a rag on the broken pane and gently break the glass with a hammer.  You can damage the wood this way.
  • Get to bare wood.  Remove remaining glaze with a heat gun, pull and push scrapers.  Sand smooth.
  • Once the glazing rail is clean, seal the raw wood with oil paint, shellac, boiled linseed oil, quick dry primer, etc.
  • Soften some glazing putty with you hands and push it into the “bed” or where the glass sits in the frame.
  • Match the glass thickness and cut it about 1/8” smaller than the opening.  Place glass over the glazing bed and softly push around the edges.  Work around the edges until the glaze is about 1/16” thick.  More is OK, less is not.
  • Install glazing pins pushing horizontally into the glazing rails, not down into the glass.  It will break.
  • Glaze the glass in.  I cannot write how to do this.  Watch a video or have someone teach you.
  • After a few hours, you can use whiting compound and a stiff brush to remove the glaze and oil off the glass.  If you do not, it is a bear to remove dry glaze.
  • Let the glaze skin for anywhere from 5-14 days.
  • Read directions of glaze.  Some need to be primed, some do not.
  • Paint about 1/16” onto the glass on both sides.  It creates a seal.


We have reached the age of frugality by necessity, where disposable is applied to everything but money.  But when you ignore a problem, mask it or say you won’t be here in 5 years, you are doing a disservice to the house and our environment.  So before you throw away a 100 year-old plus part, consider how it can be fixed for generations to come, how it saves resources and can give you a great sense of accomplishment when it is finally fixed.  It is possible to fix many parts of your house; you just need to know how they work and where to get the parts.

So be sure to do the right thing before you spend thousands of dollars, or force the next owners to do so.  If you are not handy or want to learn, contact some local professionals, because who knows, they may want to teach you.

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