Interior Storm Windows?

Ian S

Does anyone have experience with the custom made plexiglass windows that attach to the frame of your existing windows on the inside via magnetic strips? They are supposed to create an air gap that will significantly reduce energy losses for older single pane windows. I have a lot of these type of floor to ceiling windows in my older Phoenix home and it would be prohibitively expensive to replace them.

icarus

Re: Interior Storm Windows?

Short answer is,, yes.

A coule of cheaper alternatives exist however. The first is to by some 3M window insulator kits. They come in large sizes. They simply tape to the window frames with double stick tape, apply the film, and then heat shrink it with a hair dryer. They are Chrystal clear, with no wrinkles if you do them right. You can remove them and reuse them. Kits are around $10 for a pretty big peice.

Next idea is to build some simple frames and attatch the film to them to remove, or they also make clear heavier gauge clear plastic, one brand name is "flexo-glass. You can staple that to wooden frames and tension fit them (or Velcro) them in. I use these on my old fashioned multlight windows, store them in the loft during the summer.

The thing about storms, (and inside storms can be more efficient than outside ones) is that you save energy two ways. In simple terms, a single pane of glass has an R-value of ~R1. Add a wind and the R value drops to near zero! Adding a second layer of glass (or plastic) insulates by trapping air between the glass. The glass itself has virtually no r value. The R value of two panes is ~ R2, meaning that you lose less than half the heat all things being equal. But if you add a wind, you maintain the inside R value.

The other reason you can cut heat loss is by reducing convection loss from the glass. The glass causes the convection across its surface, by warming the inside glass effectively you can cut those convection loses dramatically.

All this is true in reverse in hot climates, although the effect is not as dramatic because the Delta T is likely much less in a warm climate. (in winter my inside temp might be 70f, while the outside is -40, a 110F difference. In summ in, Az you MIT have 110 out side, with 70 inside, merely a 40 degree difference. since heat loss through R is related directly to that Delta the effect is much greater in the winter.

Another side benefit of adding storms is by warming the inside, you dramatically reduce condensation on the glass. Because the cold glass is m uch cold than the air in the room, the glass then causes the air next to it to condense. At -40 I can see 1/2 of frost on the inside of my windows,, with simple storms, I reduce that to nearly none.

Tony

PS. My feeling about plexiglass is that it yellows with time, and gets brittle. Personally I would use plastic instead, cheaper, and you can replace it if you need to.

niel

Re: Interior Storm Windows?

i think i know the type you refer to as having a refrigerator seal around it and is meant to go against a steel window frame. this type of thing is good if you can get an air tight seal (refrig seals start and end so unlikely to be totally air tight) and is a convenient way to be able to remove the extra layer also for cleanings or when you need to open the window. this may do for you until you can replace the windows even if one or 2 at a time. the heat shrink plastic is better for temporary installs that you won't have a need to access to open or clean the window.

tony,
i hope you have triple pane for your windows for temps down to -40f will, as you pointed out, have a total temp span of 110 degrees from the interior to exterior. with 2 panes of glass the air temp of the air inbetween the glass panes will be exactly half of that temp differential or 55 degrees lower than 70f. 70-55 is 15 and this will cause frost on the interior side of the windows. you need 3 panes of glass for 2 air spaces which divides the temps into 3rds and would place the interior glass above freezing and would keep the window frost free. this only works if the window air spaces are air tight with no leaks.

icarus

Re: Interior Storm Windows?

Actually, I use R7 window quilts when it gets really cold, which makes a total R value of ~R9. In fact the house is so small so if we have any kind of fire over night it stays too warm to sleep even with the bedroom door door closed we may crack the window.

In our little house, the main room, with the stove is the major living area, so on cold nights we close off the other three rooms over night, and leave the fire burning gently. When we wake up it is usually ~55F. By the time the coffee is made, the temp is pretty much back up to 60 or so. Small volume, good insulation is pretty easy to keep warm. That said, of we go away for a while, it can take days to gt the cold out of the house. After being away for all of January for example. Frozen cans, with an inch of frost on them, we're still frozen several days later in th pantry!

Cold is seldom an issue,, yu can always dress for it,, heat on the other hand I don't deal with very well.

Tony

vtmaps

Re: Interior Storm Windows?

Another consideration is the distance between the storm window and the main window. If the distance is too great (more than about 1/2 inch) you can get convection in the air space between the windows. That is why double or triple pane windows have the spacing that they do. Air is a good insulator, but if you try to increase the air space you will get less insulation value in the window unit.

--vtMaps

Ralph Day

Re: Interior Storm Windows?

"...heat on the other hand I don't deal with very well."

Tony, go jump in the lake!;)

Ralph

Photowhit

Re: Interior Storm Windows?

Tony, I just checked out "window quilts" pretty neat idea, Not too cheap though. I'm working on making some 2" blue board panels to put into my mobile home type single panel exterior with a single pane "storm"ish inside window with about 3" between them. Single hung so I'll have to make some triangle pieces to go in the narrower opening and expand to fit the opening...

vtmaps

Re: Interior Storm Windows?

Photowhit wrote: »

Tony, I just checked out "window quilts" pretty neat idea, Not too cheap though. I'm working on making some 2" blue board panels to put into my mobile home type single panel exterior with a single pane "storm"ish inside window with about 3" between them. Single hung so I'll have to make some triangle pieces to go in the narrower opening and expand to fit the opening...

That should work nicely and be very effective, but may violate building code because it can be dangerous. Generally, interior foam must be shielded by sheetrock because in the event of a fire the foam may burn and emit very toxic fumes.

On the subject of window quilts and insulated panels... BEWARE of using them on east and south facing double/triple pane windows. Most of the R-value is in the quilt/panel (not in the window). If it is very cold out, the space between the quilt/panel and the window could be below zero. When the sun hits the window, that space could rise from zero to 100° in just a few minutes which can crack the window. I have never heard of that happening with regular single pane windows.

--vtMaps

icarus

Re: Interior Storm Windows?

Years ago, I bought a bolt of "warm window fabric" which I believe is still available. It is layers of quitin with silver Mylar in between that acts as a reflective insulation as well as a vapor barrier. There is a whole design on ine on how to sew rings on the fabric to make roman type shades. We have covered ours with blanket material. (we bought a entire roll of Pendleton blanket material from the mill store during a visit because it was such a a bargain,, under $1/yard for pure wool. Looked pretty funny driving down the road with this house roll of fabric that looked like a roll of carpet! Susan has made literally dozens of curtains, room dividers, blankets etc, and we still have about 1/3 of it left!)

The trick with windo insulation is to effectively seal the insulator from the glass so that you don't have a convection behind the quilt or panel. (I too have made pop in panels out of styrofoam, covered with fabric, especially useful for skylights!). My system is wider than the window opening, and has weights to hold them in place. In a pinch, a push pin to add to the seal works well. (or Velcro)

Tony