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Author: KitepKitep Date: May 11, 2008 11:59
Window cost: $144
Energy savings: $9.25/yr
Payback time: 15.6 years
Is this typical?
The $144 is just the cost of the window, and does not include installation
costs (I'm not against installing it myself).
BTW, turns out finding the price for triple or quadruple glazed windows over
the internet is harder than I thought. I couldn't find a single one. The
above is for an Anderson Silver Line 8500 double-hung window, double glaze,
low-e.
----
Now for the math. Feel free to change channels :)
R = 1 / u
loss per degree day = A * (1 degree) * (24 hours/day) / (1/u) = 24 u A
Note: I'll use DD for number of degree-days/year
loss per year = 24 u A (DD)
Note: I'll use C for cost per BTU
cost per year = 24 u A (DD) C
savings per year = 24 A (DD) C (u_old - u_new)
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Author: EeyoreEeyore Date: May 11, 2008 12:58
Kitep wrote:
> Window cost: $144
> Energy savings: $9.25/yr
> Payback time: 15.6 years
>
> Is this typical?
I believe it is.
The fastest payback for any energy use reduction method is insulation.
Loft/attic insulation pays back in a couple of years for example and blown in
cavity wall insulation is up there somewhere too.
Graham
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Author: KitepKitep Date: May 11, 2008 13:28
"Eeyore" hotmail.com> wrote in message
news:48274FE2.25E6AD3B@hotmail.com...> The fastest payback for any energy use reduction method is insulation.
> Loft/attic insulation pays back in a couple of years for example and blown
> in
> cavity wall insulation is up there somewhere too.
More attic insulation was going to be next calculation. But after being
disappointed with the windows calc, I didn't have the heart. Plus I thought
maybe my math was off.
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Author: EeyoreEeyore Date: May 11, 2008 18:10
Kitep wrote:
> "Eeyore" hotmail.com> wrote
>>> The fastest payback for any energy use reduction method is insulation.
>> Loft/attic insulation pays back in a couple of years for example and blown
>> in cavity wall insulation is up there somewhere too.
>
> More attic insulation was going to be next calculation.
Current guidance in the UK is to use 10-12" of glassfibre or rockwool mat (or
equivalent other material) for loft insulation, way more than the 4 inches or so
most people think is adequate from 20-30 year old advice. And it's CHEAP too,
especially if you install it yourself. Just make sure you don't block any air
vents in the eaves in the process..
> But after being disappointed with the windows calc, I didn't have the heart.
> Plus I thought
> maybe my math was off.
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Author: KitepKitep Date: May 11, 2008 18:39
"Eeyore" hotmail.com> wrote in message
news:482798FC.D9590851@hotmail.com...> It's well known that new double glazed windows have a compatively long
> payback
> period, although the advertising would have you believe otherwise. However
> if
> you need to replace a rotten window, then make it double glazed anyway, as
> the
> incremental cost in that case is low and will pay back in more like 5
> years (or
> less). Check out local suppliers too rather than rely on higher priced
> national
> companies.
Guess I can always hope some kid puts a baseball through my window
crossed> :)
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Author: EeyoreEeyore Date: May 11, 2008 18:46
Kitep wrote:
> "Eeyore" wrote:
>
>> It's well known that new double glazed windows have a compatively long
>> payback period, although the advertising would have you believe otherwise.
> However
>> if you need to replace a rotten window, then make it double glazed anyway,
> as
>> the incremental cost in that case is low and will pay back in more like 5
>> years (or less). Check out local suppliers too rather than rely on higher
> priced
>> national companies.
>
> Guess I can always hope some kid puts a baseball through my window
> crossed> :)
Good Luck with it anyway whichever route you take.
One other nice thing about double glazing is they you're relatively unlikely to
get condensation (and possibly resultant mould) from condensation on the window
pane.
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Author: Paul M. EldridgePaul M. Eldridge Date: May 11, 2008 20:27
On Sun, 11 May 2008 14:59:31 -0400, "Kitep"
no_where.com> wrote:
>Window cost: $144
>Energy savings: $9.25/yr
>Payback time: 15.6 years
>
>Is this typical?
>
>The $144 is just the cost of the window, and does not include installation
>costs (I'm not against installing...
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Author: KitepKitep Date: May 11, 2008 21:22
"Paul M. Eldridge" wrote in message> I've only skimmed through your calculations, but there appear to be
> two key factors you've overlooked. One is the operating efficiency of
> your gas furnace or boiler; to account for this, multiple the number
> of BTUs per CCF by the AFUE rating of your heating system -- if, for
> example, your furnace's AFUE is 80 per cent say, then your true cost
> per MM BTUs is 1.25 times higher than what is shown here. In
> addition, your cooling costs per BTU are likely to be very different
> from those of your heating, so they really should be treated
> separately.
Good catch. I'm not sure what my natural gas furnace operates at, but since
it vents through the wall instead of through the roof, by code it must be
93%% or better (I think).
So 93%% -> 1.075 multiplier, and my $9.25/year should really be $9.94/year,
payback time = 14.5 years. That's a year better than before, but still not
enough to make it worthwhile.
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Author: J. ClarkeJ. Clarke Date: May 12, 2008 05:09
Kitep wrote:
> "Eeyore" hotmail.com> wrote in message
> news:482798FC.D9590851@hotmail.com...>> It's well known that new double glazed windows have a compatively
>> long payback
>> period, although the advertising would have you believe otherwise.
>> However if
>> you need to replace a rotten window, then make it double glazed
>> anyway, as the
>> incremental cost in that case is low and will pay back in more like
>> 5
>> years (or
>> less). Check out local suppliers too rather than rely on higher
>> priced national
>> companies.
>
> Guess I can always hope some kid puts a baseball through my window
> :)
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Author: daestromdaestrom Date: May 12, 2008 15:08
"Kitep" no_where.com> wrote in message
news:48274214$0$5173$4c368faf@roadrunner.com...> Window cost: $144
> Energy savings: $9.25/yr
> Payback time: 15.6 years
>
> Is this typical?
>
> The $144 is just the cost of the window, and does not include installation
> costs (I'm not against installing it myself).
>
> BTW, turns out finding the price for triple or quadruple glazed windows
> over the internet is harder than I thought. I couldn't find a single one.
> The above is for an Anderson Silver Line 8500 double-hung window, double
> glaze, low-e.
>
> ----
>
> Now for the math. Feel free to change channels :)
> ...
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