WINDOWREPAIR .COM, INC. The Draft Test
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WINDOW DRAFTS - THE REAL STORY:
The most frequently asked window question: "My old windows are so drafty - should I replace them?" What few people know is that old windows weren’t originally intended to be airtight. They were intended to close, lock, and shed rain, and were an improvement over older designs. But there are ways to make them as airtight and energy efficient as new windows! First you need to answer the question, "where are the drafts coming from?" 
ON A WINDY DAY:
FIRST TEST- Put your hand or an open flame near the pulleys; if there is air coming through them the source is through the exterior trim of your house, bypassing your storms, original windows, and allowing wind and moisture inside the walls! SECOND TEST- Put your hand or an open flame near the edges of the original windows, where the sash (the part that goes up and down) meets the stationary trim; if there is a draft here, it is from your storms! Either the caulking which is supposed to seal the frame is dried up or they are "70's style", in which the panels to do not have any channels to keep the wind from blowing around their edges. When sellers of replacement windows claim their product will save on your energy bills they are comparing their window to an old one, before restoration and without a good storm! We contend that a weatherstripped old window with a tight storm can match the performance of a new window. And furthermore, that all of the add-on technology they tout is just icing on the cake- the majority of energy savings are gained in stopping drafts and creating a seal between two pieces of glass, which can be accomplished keeping the old window. Here is a graphic illustration of the draft problem I witnessed- The homeowner had allowed a plumber to make up this process whereby he replaced all the old glass in the wood sashes of an 1885 Victorian with double insulated glass. He then had to fabricate lead weights because the extra glass of course doubled the weight of the sashes. He threw away the storms thinking this they weren’t needed because he had created an energy efficient window. So there was the customer on a windy winter day with his curtains blowing around and his rooms freezing and his heating system working overtime because there were no storms and no weatherstripping! This case proves my contention that stopping drafts is at least 2/3rd’s of the battle! In our opinion at windowrepair.com stopping drafts is the primary energy saver- and the replacement window people when comparing their window to an old one they are comparing the old window with no weatherstripping and a leaky storm- so this is why they can claim a huge saving when throwing away old ones and putting theirs in. We also contend that their weatherstripping is not permanent. All tilt-sash replacement windows use felt type strips to seal the edges of the sashes. This is subject to wear. And many of them use a soft foam backing to create pressure and tight seals- this foam gradually collapses leaving gaps all around. When you go back to the original, scientific way of evaluating window energy heat loss the truth is uncovered. They found 4 different processes- all distinctly different problems with different solutions. Of course, this is way too complicated for a salesman to deal with and the fact that drafts is the most important did not suit their purposes. So now window performance is evaluated by an arbitrary “U-Value”, which combines all the forms of heat loss. But, drafts are solved by component tightness and weatherstripping- and all the argon gas, double glass, low-E technology they want to sell does not have any effect on drafts (infiltration). The following is taken from the materials provided for the energy efficiency classes I took in the early 80’s, based on government funded research. The original ways of calculating window energy loss included 4 separate scientifically measurable processes; Conductance, infiltration, convection and radiation. U-Values just lump them all together! Conductance is expressed as “R-Value”- each single pane of glass is assigned arbitrarily one R-Value. Therefore, it makes no difference to the R-Value of a window assembly whether this glass is an old window and a storm or a double insulated new glass unit. Radiation is a complicated process and is not affected by changing the windows much; convection is just the fact that glass conducts cold so it presents a cold surface to the room. None of these processes are the same as a draft. Because cold air falls and warm air rises, this can create a circling of the air in the room, falling off the windows, rising at the other end, feeling like a draft. But a draft is really whatever gets through the gaps in the structure of the hole in the wall we call a window. The original government research showed that the gaps around an old window without weatherstripping amounted to a 5 inch square hole in your wall! Imagine your living room or bedroom with 3 or 4- 5 inch square holes in the wall on a winter night! That is why this is the major source of heat loss in an old window. 
This is just our opinion based on 25 years of experience. Because the R value is the same whether it’s two pieces of new glass or an old window and a storm; because convection and radiation stay pretty much the same no matter what kind of window and can be stopped by shades or drapes; infiltration is the biggest loser. These are the figures I was given, based on government funded research during the energy crunch of the 70’s:
R- Values of various wood window configurations; When we say a “good” storm has to be part of making an old window as good as a new one, we mean a storm like the Harvey Tru-Channel- guaranteed to admit no more than .01 infiltration. This is because the Harvey has a full perimeter and center u-channel interlocking system which does not allow the wind to blow through. Your old storms are what we call “4-point blow-bys”. They are secured only at the corners, and when the window blows it bends the sides out of the frame. You can prove this by going on the outside of your house, and pushing on the edge of a storm panel. Watch it bend! That is your curtains blowing during a nor’easter! |