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I am in the process of purchasing 20 replacement windows. In researching, I am confused about the benefit of low E argon gas in saving energy costs. For example I live in Md and looking at some gov sites. the energy cost using a mid grade window with a U-value of .49 and SHGC of .59 is $1275. I add have low E and Argon gas with a U value of .34 and SHGC is .30 the cost is $1269 a savings of 8 dollars per year. If you look at the high grade triple pane u value .11 and SHGC .34 the cost is $1146, a savings of $129 or about 11%. If the mid range window costs about 300-400 to install and the additional cost for low e is 50 dollars. I will be spending 1000 to save about 100 over a ten year period. If I go with the high grade at a cost about 400 more a window then I will spend $8,000 to save about $2000 over a 10 year period. Tell me where I am wrong.

You didn't go wrong. My bills are 4x what the model program tells me. $918 or something per year they come up with, I'm spending over 4K per year(big old house).

What you will actually save has several variables. Windows account for 50% of your annual heating and cooling costs. Figure out on an annual basis what energy you are using. Find your U value for what you currently have and this will give you a general idea. I have used this formula and found it to be pretty darn close.

$3000 per year, 1500 for window energy. Current U = 0.89, new U = 0.34

0.34/0.89 = 0.38, multiplied by 1500 = $570 window energy cost (U=0.34)

annual savings = $1500 - $570 = $930.00

Some companies will give you a 25% fuel savings pledge, which on $3000 would be $750 as they leave room for the variables such as attic insulation, number and locations of windows, etc...
If you have air conditioning, the 7-10 days you need it, the LowE will help as it is a measure of heat transferance through a material, in this case, glass. I would not bother with SHGC to simplify your search.

Triple pane is usually out of proportion in pricing for the overall gain, however, if our energy cost doubles or worse, it may be a wise INVESTMENT if you plan on staying in your home for awhile.
Hope this helps.

jtfpie

The numbers and information you supplied may have been inaccurate (as there is not a residential triple-pane available with a U-.11). I applaud JScott's calculation method as it is more than likely closer to the actual amount saved. Both however, are guess-timates. Even though the gov. sites provide calculators that they had developed by well-respected labs, they are designed to run extremely general performance numbers and are not supported by actual. Even the most advanced computers can't pinpoint the results of Mother Nature or anything in her path, let alone when you combine that with man-made structures.

As JScott stated, windows "MAY" account for 50% of your wasted energy, but may be much less or much more. The only way to know is to have your house tested with a certified energy audit. Fuel savings pledges are also guess-timates and are always limited to a very small percentage of the purchase amount (typically under $500 total payout)... cuz they aren't sure either.

As also previously stated, Low-E is NOT a measure of heat transference through a material... that is U-factor. Simply put, Low-E is a metalic coating used to reflect heat (energy) back to it's source. Additionally, I would not recommend ignoring the SHGC as suggested. Depending on your area, it can make a tremendous difference.

In short, a little knowledge can be a dangerous thing. You can over-invest or under-invest without a complete understanding of how your home works. I'd suggest alot more research or bring in a qualified specialist to help guide your decisions. Good Luck.

Fenex

fen,

Thanks for your response, on the u=.11 was my bad it is actually .18. The website is was using was efficientwindows.org. It allows you to input your city and compare different windows. It even shows some mfg. I know the numbers are just an average but I was looking for a guide to help cut though the sales BS. Since my windows are 50 years old and in poor shape I am expecting about an 30% savings. I am just not sure if it makes sense to upgrade to the coatings or buy the most expense windows.

Thanks FenEx. I did mean to define U value and not LowE. Dislexia I guess. The guestimate calculation works well in my area and may not work well in yours. The basic laymans theory behind U values windows and energy costs was explored. Products in my area with a good U value traditionally have an acceptable SHGC. I am also understanding from literature that the farther north you go the less importance of SHGC comes into play with more emphasis to U values.

Can we get a FenEx checker on this board(its like a spell checker )

50 year old units would be either wood, aluminum or steel with single pane glass. You should see a significant savings replacing the wood and a mondo-dramatic savings if you have steel or aluminum. The U value of 0.18 is very good, actually its rare. In addition to energy savings there is one thing you can't put a real dollar value, comfort. Your home should much more comfortable.

jtfpie and JScott

I wouldn't install a window anywhere in this country without atleast 1 Low-E coating and atleast Argon. The benefits of Low-E go well beyond solar heat gain. They also reflect ambient heat off the surface of the glass and back towards it's source... in and out. I would however recommend the Low-E be applied to different glass surfaces depending on North or South climates. The gas fill serves an insulating purpose like the insulation in your walls. Would you invest in a room addition and skip wall insulation? It wouldn't be a wise decision.

Your home is YOUR controlled space that separates you and your family from the elements just like prehistoric man used a cave. Only we have better technology now... and carpet. I always stress that individuals see their home's shell as serving that purpose first and foremost. Simply put, protect and separate your inside from the outside the best you can... that's why we live in homes. It will not only save you money... it will greatly increase your comfort.

Don't make the mistake of seeing a more expensive window with a better performance rating and assuming it's only due to the glass like most do. The top performers in the industry also provide better frames and hardware and will last much longer. As you continue to research and learn what makes each clock tick and why, you will see the differences and values.

Fenex

Very well put. Thankyou.