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drew2000 02-06-2012 03:54 AM

Measuring efficiency of builder grade windows?
Hey Guys,
Our townhouse has many (18) windows, it was built in 1993. The windows are original builder-grade double-glazed metal windows.

I measured the temperatures of the windows and surrounding walls with an infrared thermometer. The windows are definitely a source of cold air in the house, the glass and metal are 10-15 degrees colder than the surrounding sheetrock.

Before I go out and spend $$$$$$ on new windows, I want to make sure new windows will really help keep my house warmer.

My question: Is there any way to measure the U-factor or other properties of my existing windows so I can compare them to what the salesmen quote for new windows?


Aaron5454 02-09-2012 05:21 PM

I may be wrong, but the NFRC (The National Fenestration Rating Council) has a website that does ratings for stuff like this. Don't remember the URL, but I seem to remember them actually rating windows by manufacturer.

Not sure if there is a good way to directly measure.

mudmixer 02-10-2012 10:55 AM

A windows will ALWAYS be colder than the walls in cold season. That is because a window is just a hole in the wall with some glass and gas in it. No matter what kind of gas and panes are used, the U-value will never be equal to any minimal wall. Just look at the listed U-value and compare it to the U-value of and uninsulated 8" concrete block and it will be about the same.

Also, they never tell you about the radiant heat loss that is very high at night in cold climates. Just a sheet hanging up at night does more good than any "gas" because the heat is radiated way through the glass from the source to the colder and darker area.

The metal frames also contribute to the heat loss because of conduction through the exposed aluminum, but a gap or vinyl barrier will give some minimal insulation.

I have a very good, tight and properly installed oversize sliding door. There is a world of difference at night just from dropping the 1" mini blinds down and tilting them, and it is instantaneous.

Just face it - If you want to see outside, you will lose some heat and there are limits on what you can expect from a window and a good installation can make a bigger difference than the salesman's numbers on insulation or U-value.


drew2000 02-12-2012 02:47 PM

Thanks for the replies guys. I am definitely wary of the window salesman. That's why I was hoping to figure out how my current windows rate compared to new ones.

I don't trust any window salesmen period. I don't want to sink $10,000+ into new windows and still have the same problems.


nealtw 02-12-2012 03:45 PM

When we work around windows that are twenty years old, fixing rotten wood and the like we encourage people to change that window because we are there already and the labour is no difference. Nobody comes back and says, that room is so much warmer with the new window.

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