[MassHistPres] More window material

[Chris Skelly]

I think making any assumptions on the "infiltration" factor of an old window
demonstrates that this worksheet is misleading.   Just because a window is
old doesn't mean it has to leak air.  

 

Would we use this logic to demonstrate how much money we would save by
buying a new car?  If comparing how much money you would save on automobile
fuel, you would need to consider the miles per gallon of the old car and the
miles per gallon of the new car.  All old cars don't have the same miles per
gallon and all old windows shouldn't be treated with such a broad brush
either.  Furthermore, the infiltration that will occur over time with a new
vinyl replacement that warps and bends needs to be factored here as well.  

When it comes to saving energy on heating a home, infiltration is a major
issue that needs to be addressed.   Yet when it comes to old wood windows,
infiltration can be addressed very effectively through a number of methods.
Methods such as installing removable rope caulk each fall are very
inexpensive.  For those on a tight budget and faced with leaky windows, this
can make a huge difference.  Chris.

Christopher C. Skelly 
Director of Local Government Programs 
Massachusetts Historical Commission  
220 Morrissey Boulevard, Boston, MA 02125 
Ph: (617) 727-8470 / Fax: (617) 727-5128  
Christopher.Skelly at state.ma.us 
http://www.sec.state.ma.us/mhc/mhcidx.htm 
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-----Original Message-----
From: masshistpres-bounces at cs.umb.edu
[mailto:masshistpres-bounces at cs.umb.edu] On Behalf Of slater at alum.rpi.edu
Sent: Friday, September 25, 2009 12:04 PM
To: masshistpres at cs.umb.edu
Subject: Re: [MassHistPres] More window material

 

Maybe someone can help me out here. I just did this worksheet for window
replacement:

http://www.dnr.mo.gov/forms/780-1363.pdf

Based on my calculations, it told me that a house with 30 single pane
windows with storms will consume 582 gallons of oil -- just for the windows
-- and that if you install low-E replacements, it would consume just 233
gallons of oil just for the windows. Replacing would save 439 gallons of oil
annually.

Let me tell you my assumptions and maybe someone else can try this.

First, I assumed 30 windows at 32" x 62" -- each being 13.9 square feet.
That's about the size of my second floor windows. Multiplied by 30, that's
417 square feet of windows. 

Second, I used 0.5 U-value for single pane with storms, 0.38 for double-pane
with low-E glass. That's an agreed upon number.

I used the "degree days" method in line 6, since this form is for Missouri
and we are in Massachusetts. The calculation says "degree days x 24 / 10^6".
I used 6250 degree days, a number I got from an energy website. That changed
the factor to 0.15 versus the 0.1 for Missouri.

I used an energy cost of $19.73 per million BTUs. That was based on oil
being $2.75 per gallon. It came from this website:

http://energy.cas.psu.edu/costcomparator.html

I treated the fuel efficiency as 100% in the calculation because the energy
cost from the previous step already factored that in.

I assumed that a vinyl replacement window costs $300 installed.

Using the formula on the spreadsheet, it said that if I keep the original 30
windows, I will spend $1,849 in heating costs, and if I replace them, I will
pay $641 in heating costs.

If that's true, that seriously weakens the argument for keeping the
originals pretty significantly -- if a replacement window costs $300, then
payback period is just 7 years. If oil goes up by 45% to $4/gallon, then the
payback period is just 5 years.

One big factor is that the calculation uses something relatively new (it
wasn't on an earlier version of the form) called an "infiltration factor".
It is set to 1.00 for old windows, 0.14 for new windows. That seems a little
arbitrary, and it completely changes the results of the calculation. Without
this factor, a replacement window without low-E glass is actually less
efficient than an original window with storms. 

I did some research on "low-E" -- there is some thought that it does not
last for the life of the window, and may only last for 5-6 years before
breaking down. 

Can someone else validate my numbers? Honestly, they are just not that
believable. I have 49 windows in my house -- some of them are quite leaky,
such as leaded glass casement windows -- with storms, though the leaded
glass transoms above them don't have storms. I also have several windows
without storms -- two 2nd floor bathroom windows and a casement window over
the kitchen sink, plus a fixed window with multiple lights, plus a couple of
3rd floor casements that open inward. Many of my windows are larger than the
example I used too.

I use about 1,200 gallons of oil per year to heat a 4,000 square foot house
to around 65 degrees. If I plug 50 windows into to this worksheet, it says
1,100 gallons of that is due to the windows, and I would save 718 gallons
per year by replacing them.

I just can't believe that on its face. Could these calculations be designed
to justify replacement?

Ralph Slate
Springfield, MA 

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