I was thinking about adding an extra "pane" to some of our windows in winter. This would be similar to how those plastic shrink-wrap kits work, but I'd using something more permanent like a simple piece of plexiglass with a rubber strip on the end to hold it into the inset of the window. (Perhaps something like an interior storm window. Does this make sense to do? We've already got triple glazed windows everywhere (except on one door and WOW can you feel the difference) but thought one more layer might help. In our old house (very drafty, with single-paned windows) I used to put Roxul in garbage bags and fit the 'blocks' into the window sills of windows I might not miss so much through winter (basement, mostly). That helped enormously but in this case I don't want to black them out entirely but would like to reduce heat loss, too. Thoughts? Thanks! -Colin.

I prefer to add a "storm" to the outside because if you get any condensation or they leak the outside of the existing window is meant to be exposed to the elements anyway. If you seal them from the inside sometimes you can get condensation or moisture between them causing mold or damage to the woodwork. Having said that we had two crank out windows in our last house and couldn't put storms on so I had a pane made the exact same size as the insert screen that fit in the windows on the inside. I ended up just adding a bit of colored electrical tape (to match the trim) and just slid them snugly in place. I had to use a suction cup to get them back out. It worked well and I didn't have any condensation issues.

Realistically the cost of a shrink on plastic window sealer ends up being less, about $2 a window a year or the panes I had made were about $80 each so the payback is what, 40 years? The big advantage is I could pop them out when I wanted to open up the window and it only took a minute to pop them in or out compared to 5-10 minutes with the window shrink sealer and removing the tape. Also the glass was clearer.

Thanks Brock,

Our windows are actually flush to the outside so there's nowhere to put a storm on the outside.

Did you opt to use glass instead of plexiglass?

It's sort of implied in your answer but: you've been happy with the results? Your efforts cut some of the cold?

Thanks,
-Colin.

Yes we used glass instead of plexy, at the time it was less expensive. The two rooms were identical in size and both faced north. If I had the "storm" out of one you could tell sitting in front of the window.

About the windows being flush on the outside our regular ones were but they made the storms stick out. The bowl shaped in a way. The edges sat right against the existing window frame, and then the storm frame went out (away from the house) about two inches. The added glass sat there. So as you looked at the side of the house the storms stuck out further than anything else, but they worked well.

You've already got triple panes. What do you think the current u value is and what do you think it will be after adding another pane? It's difficult to imagine any comfort or financial gain from a fourth pane.

I think he has some triple panes and likes then and wants to do something with the older single pane windows.

Maybe just replacing the windows? I think that qualifies for the tax credit.

Nope they are all triples already (Fibertec, U0.18 and U0.13). But the heat loss on a window is still so high compared with the rest of the house (3"/6"/3" Nudura ICF, ~R40-50 equiv.) that it seems like an extra layer really could make a difference.

Well, I think I'll try to build at least one insert, and then do some measurements on differences in surface temperature and the air at the base of the window and see what I see. (I'll try get to back to this thread to post results.)

Thanks!
-Colin.