[energy_rater_La]

Do you have an opinion about double-pane windows as compared to window coverings as far as keeping out heat?


that is pretty general..as is asking for an opinion here!
What type of windows do you currently have?
single pane?
what type of window frames?
what is your location?
what are the recommended R-values for insulation in your climate?

it will always be better for old windows to keep the heat from entering the window.
once the heat enters the window and the space to be conditioned it is harder to condition the living space.

there can be up to a 20% savings just by plantings that shade windows in the
summer. for instance I have bananna trees that get high enough by mid July to
shade the front windows and front door.. in the winter I have a windbreak of
evergreen trees. the former has more impact than the latter..because of the length
of the cooling season in my location. I consulted a solar plantings guide for some of the
plantings, others were just luck!

single wood windows get a bad rap all the time. but they can be weatherstripped
caulked and sealed pretty well. once this is done window tints can be installed
to reflect heat out..my climate or into the house..for cold climates. these tints
have improved a lot in the past few years.

single metal windows may be newer, and have a tighter fit as far as air leakage but the metal frame conducts heat/cold which makes these windows a real hot/cold spot.

single windows always condensate and in extreme cases can rot out window sills &
cripples under windows.
in the summer the glass condensate to exterior..in winter to the interior. simple thermodynamics.
it is when you step upto a double paned window that the condensation
is stopped..in most cases..by the insulating air space between window panes.
adding low e and argon gas improves the thermal efficiency of the glass..
selecting the proper frame is also important.
wood frames & vinly being poor conductors of hot/cold is a better choice than metal
frames which is an excellent conductor of hot/cold.

best of luck.

 

[energy_rater_La]

A storm window over a single pane window will increase the U-factor by .5 or from .5 to 1.0 which in terms of stopping radiant heat is virtually nil.

the reason a double paned window performs better than a storm over a single pane
is that the two panes are close together. lowe and argon help to keep air at rest
and glass unit is sealed.
the larger the gap between two window panes such as storm over single pane window
the more convenctive current between the two glass surfaces.
these windows perform no were near the same as an insulated glass unit.
as stated lowe argon windows have ufactors and solar heat gain coefficinets of
.30 and less..a single glass window with a storm will be at least .50 and higher
depending on if the window frame is wood or metal. metal conducts wood doesn't.

powerstroke you should take a look at the thread I started on a home that just
changed windows and the actual savings..not huge..something like 14.8%
energy savings..not the best investment nor bang for the buck.

 

[energy_rater_La]

numbers from Remrate the software Resnet mandates
for raters:
single wood uvalue .90 shgc .65

single wood with storm uvalue .80 shgc .50



single metal uvalue 1.30 shgc .80

single metal with storm uvalue 1.09 shgc .72
(differece in uvalue is conductivity of metal frame)



double lowe vinyl frame uvalue .36 shgc .35

double low e argon gas vinyl frame uvalue .30 shgc .30

I'm no expert, but I do know that the distance between the glass
panes is directly linked to performance.
in an Insulated Glass Unit (double paned or triple pane) the air space
has a minimum and maximum distance. Too close and there is an issue..
too far and convective currents set up between the panes. this lowers
performance.
IGU's and single windows with storm windows are different dynamics.

now a good investment in my climate is a solar screen...next to plantings
awnings & exterior shading the solar screens beat the heat before it enters
the building envelope (where it costs to condition this gain)
heres arnother example (again from remrate library)

single metal with solar screen uvalue 1.09 shgc .50
solar screen lowers shgc by .30 as compared to single metal window.

these numbers are the ones we use for existing homes deciding
between changing windows as opposed to solar screens or tints.
it all depends on homeowner's intent and condition of existing windows.

new window info can be modified within remrate based only on NFRC (national fenestration rating council..pardon mispelling) info.
even with uvalues and shgc info on NFRC sticker, we still test air tightness
and verify numbers.

(shgc solar heat gain coefficient)