My house as a wall with several large windows made up of many small
panes of glass. The windows are all non opening. The past owner put a
second glass panel on the outside of these windows - a storm window if
you will. These are just mounted to the side of the house - no air
tight seal or anything and can be removed with a few screws. My
question is what are they doing temp wise to my house (In New Hampshire?).
In the summer I see them just creating a 'hot house'' in the space
between the 2 sheets of glass making the place even hotter. In the
winter, with the interior glass sealed and non opening and regular
drafty air in the space between the 2 sheets of glass, I don't feel any
increase in insulation or warmth.
I am thinking of removing the outside glass panel permanently - or at
least in summer. What do you think? Will this help keep the place
cooler in summer and not much different in winter?
That area in-between is a dead air space, insulation. That second layer
of glass and the insulation of the dead air gap is helping keep your home
cool. Removing it will increase the heat load in your home.
Think of it this way. All the heat that is warming that air space would
be inside your home without that storm window. It would not be so hot, but
only because it would be spread out all over your home.
Be cool keep it were it is.
On Sun, 1 Apr 2007 10:56:17 -0400, "Joseph Meehan"
That doesn't make any sense. If the air trapped in the gap is hotter
than the normal outside air, then the inner pane will be conducting
more heat than it would if the outer pane weren't there. For
INSULATION effects, you'd expect something like: Outside air: 90dF,
Inter-pane air, 80dF, indoor air, 70dF. Or the reverse, in the
winter. I suspect that the storm windows are helping a little in the
cold months, and making matters worse in the warm.
It's possible that the outer pane is blocking enough longwave
light that they're doing some good anyway, But I'd take the "storm
windows" off during the cooling season, and replace them during the
Put up light-colored screens during the summer. That should
bounce a fair amount of light away, and not trap warm air
against the inner window.
Either that, or modify the storm windows so that there's a
1/2" gap at the bottom and top, which will allow an actual
current of air when it's hot, and thus prevent heat build-up.
Plug the gaps in the winter.
Yea, it is a little odd but true.
What is happening is that some of the energy (heat) that is going past
the first window is being trapped between the two windows, the rest goes
into the room. That energy between the windows will move to the cooler side
of the glass which is likely both the inside and outside. With only one
window ALL the energy (heat) that goes through the window ends up inside the
home making it hotter. It does not get as "hot" inside only because the
heat is distributed over a much larger area.
Well... maybe. Depending on what kind of glass is in each respective
pane. I still think that if you have reasonably low-E windows and
cheap plastic storms, you're losing ground. but maybe not.
You'll still get better results with a screen or a vented
outer pane that doesn't trap hot air against your windows.
In the winter, you WANT that bubble of hot air. In the summer, you
On Mon, 2 Apr 2007 20:50:37 -0400, "Joseph Meehan"
Ok, but that doesn't mean that it's a helpful scenario.
Thermopane windows are primarily designed to keep heat *IN*. They
depend on low-E films and similar treatments... Well. let me try some
sample numbers . . . .
Ok, apparently, the inner pane has to be around three times better at
converting light to heat than the outer pane for it to make matters
worse. So if both panes are the same material, you're definately
better off with multiple panes, even if you are trapping hot gas
between them. (The difference between energy reflected and
energy converted is too complicated for be to bother modelling,
esp. if I'm conceding the point on the basis of the simpler
There was thermopane before there was low-E. (And isn't that still
It was just plain window glass glued together with air in between. It
was meant to be like a storm window but more convenient. When you
opened one pane, you did the same to the other pane. So if you wanted
fresh air, you only had to move one thing.
And also very good for doors. We had a big sliding glass door, but
there was no reasonable way to make a storm door for it. Thermopane
And it was meant mostly to keep the heat in, because we didnt' have
AC. For those who had AC, it would also keep the heat out.
There is no need to remove the storm windows until you actually want
to open the entire window for fresh air. The only other reasons are
for repair and replacement.
You say they are just mounted to the side of the house but that is
hard to understand. Are you saying that it is fastened directly to
the siding? Directly to the window frame? Are the edges of the frame
exposed or do they sit into a dado (ledge) in the window frame?
There is no tight seal, but the window is close to the wall or the
real window, right? What would you say the widest distance is, or the
total area of opening between the added window and the things next to
If the air isn't moving much in and out of the space between the two
windows, then it is almost as good as having a storm window, which
provide insulation during the summer and winter. Sure the air is hot
one the inside of the outer window, but if the outer window were not
there, it would be hot on the inside of the inner window, right in
If the window doesn't fit tightly, especially if there are openings at
the top and the lower side or the bottom, the air will get hot, or
warm in the winter, and rise and flow out to be replaced by new colder
or cooler air. But that will take some time and I suspect even then
the windows will be at least 50% as effective as good storm windows.
You could get an idea of how much the air is moving inside by holding
a hair in the crack, maybe a blond hair, maybe a long hair, I haven't
done this, but just like one can see a flag blowing in the breeze,
there is bound to be something that will give a visual idea of how
much the air is moving. It probably varies, but I'll bet it is not
that much. In January I asked here about the speed with which warm
air exits a building and is replaced by cold air, when a big 18 foot
high 12 foot wide garage door is opened. It's not that quick. Close
the door after 30 or 60 seconds and the building seems just as warm as
it was in a minute or so. That's with an enormous door wide open.
Cracks around storm windows will let air in and out, but it won't be a
breeze, just a trickle maybe.
We used to have casement windows with storm windows and they got
condensation inside. We had to clean out the little air vents
(clogged with insect silk) so that the air could circulate enough to
prevent condensation. Thermo-pane hadn't been invented yet, and that
is better and more convenient, but those storm windows still
accomplished 99% of what thermopane does, I'm sure.
You can get your hand in the crack?
Bigger "crack" then I expected. You could get some foam rubber used
for insulation and run a strip of that around the window. It comes in
fairly narrow strips, in white and grey and maybe another color or
two. Maybe just try one window and see if it makes a difference.
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