Window heat loss

Patrick

To be honset, never even heard of interior storms. Can you explain?

I currently have the 'ol triple track types on my house (already installed when bought house) I will soon replace storms and windows with replacement windows, etc. But the storms do a decent job of cutting down wind draft. Or at least keep the old wooden sashes from flat out falling out of their openings ). Just kidding.

Aside from old triple tracks, I have seen more modern day strom windows that I'm sure way outperform stroms of yester-year.

They have their place...

... interior storms can frequently be found in historic districts where local zealots demand old windows not to be obstructed by modern storms. Thankfully, our historic commission is more concerned about the welfere of the original windows than the storms that would protect them.

The biggest issue I have heard of when it comes to interior storms is condensation. While that can happen on the exterior storm as well, it's easier to drain the condensate out there, where gravity, etc. can do their thing. On the inside, the condensate can lead to rot.

Now, if the windows and frames were air-tight (unlikely) then perhaps the condensation issue would largely go away. But windows being windows...

Great-

So if I'm unable to get a good seal with the primary windows, it's better (from a condensation point of view) to have interior storms- as long as they're tight, right?
As an earlier poster quessed, this is a historical district situation, and in most cases the permanent tracked storms wouldn't have worked, anyway.
Thanks,
Patrick

another timely post brad

I'm winding up my own heat calc and the hydronic institute H-22 Guide I use lists double glass wood or vinyl windows at U .341 (low e's at .263) so maybe I'll rethink that.

Thanks,

David

I personally would not waste my money on storms interior or exterior if you forsee new replacement windows in the next few years.
When you get ready for windows , get a lot of prices..Lot of companies selling the exact same window at all sorts of varying prices.
Around here some companies sell their windows for 900-1200 each installed,and it is usually the same window a smaller company will sell you installed for 500-600.
New windows let a lot of daylight into a home that old glass blocks out..My customers are amazed at how bright their home is now.And all of them brag on the new comfort and appearance.BTW I sell and install Alside brand windows.

Condensation the where and why

The general rule on condensation with storm windows is this:

If the condensation occurs on the inside face of the outside pane, it points to the interior window being leaky. Moist interior air finds the colder surface on which to condense.

If the condensation occurs on the inside face of the inside pane it generally points to a leaky outer window, allowing the inner window to cool below dew-point.

So if your outer windows are so-so (as is your local Hysterical Society) then yes, interior storms are the way to go and sealed as well as you can.

Interior storms.

> Anyone have opinions on performance differences

> between interior versus exterior storm

> windows? Thanks, Patrick

Interior storms.

I've built nothing but interior storms, as the windows I've restored are all pre-wwII steel casement windows. Usually Truscon or Fenestra. The interior storm covers the entire daylight opening. Since the storm window is on the interior you can use acrylic since it won't see very much dirt, weather, and UV. On the interior, the acrylic won't yellow prematurely (at least 18 years before visible yellowing). I always recommend the scratch resistant coated acrylic.
The acrylic's R value is better than glass, its much better at blocking UV, and it has better low E properties than glass. Particularly since I use 1/4" glazing with minimal framing, or no frame at all for moderately sized windows or smaller.

The low carbon content of the steel used in those old casements can weather very well. The house I live in has these. As they were, they were intolerable to use, or live with. I used an aircraft lubricant on hinges and hardware, stripped most of the paint off with a razor (it was surprisingly easy), knocked most of the glazing compound out, primed everything with oil base paints, reglazed, repainted. Whew! Oh. and I made my own seals with caulk (ask if you want details). Its really easy but no one thinks of it. But I did these windows 16 years ago and they are just now starting to chalk a bit. They are no worse for their wear after 68 years in the weather.

Subjectively (comfort level near the window) and objectively (thermal imaging) these windows are outperforming my neighbors' replacement windows (with the exception of the ones with so many coatings and shadings that the interior of the house is downright gloomy. Could never live with that. I'll close the drapes at night for the same effect, thank you). And the sound isolation is much much better also.

But I agree, more fragile historic windows, particularly wood with lead-came inserts should get tasteful exterior storms.

-Terry

Basic physics

Radiant heat transfer is just that- "radiant" and not "conduction". "Transmission" heat loss or gain is normally only via conduction. It all depends on how window manufacturers express their catalogue performance data. The "U" value is a thermal resistance value which is based primarily on conduction of one temperature on one side of the window to another temperature on the other side of the window. The normal heat loss and heat gain estimates use the ambient air temperature on one side of the glass to the other. But the missing gap is that the actual temperature of the glass surfaces may not be the same as that ambient air temperature, so you can have some fairly high differences in actual total heat transfer when the radiant component is taken into account.

Interior Storms

Check out Windo-Therm out of Hoosick, NY. They make a two layer clear plastic interior storm that stops pretty much all infiltration and has a very good R-value.