Where are these modern windows leaking and how to fix it?

Question

Even in my moderate climate zone this dreaded winter starts and one room in particular (the living room) drives me nuts: It feels so terribly cold, I can "feel" small drafts but no obvious source. The most obvious one are the windows though and just holding my hand close to the windows I can feel a cold draft coming towards me ... and this with a measly 55-60F outside.

It is a 100 year old house but has dual pane retrofit vinyl windows (I think from the 90s or 2000s):

Here is another zoom:

I really don't see any obvious holes or issues. It is always suggested to "caulk around windows" but where? I can buy a foam pad and put it under the sash. But I don't think this is the main issue, it's not just from under the bottom sash.

Where could this window be leaking air and short or replacement, what is the most efficient way to seal it? We never open these windows so it could be a solution that does not require the sashes to be movable.

Answer 1

There are several possible issues here.

1. Though the windows are sealed units, you are feeling convection currents from warm air at the top of the room being cooled and dropping to the floor. This is unlikely as this is happening at a modest 60F.

2. You have air infiltration through the window unit itself. Double Hung windows are notorious for their air infiltration. You can test this by covering the inside of the entire window with plastic. If the plastic billows in, this indicates poor wiping seals or seal contact on the sashes. Close inspection is then required to check for worn weatherstripping or missing weatherstripping plugs that close gaps where the two sashes meet.

3. You have air infiltration through the window frame. These windows appear to be inserts into the existing casing. You are then at the mercy of how leaky the wall is that contains the window frame. You may be able to mitigate this somewhat by removing the interior trim around the window frame and using expanding foam to seal between the rough stud opening and the window frame. You should also make sure that the exterior caulking is in good condition around the window frame as well as the window insert.

Answer 2

You can get "heat shrink film window insulation kits" which are best applied to the outer edge of the window frame (inside the house) to catch as many of the "window to frame" leaks as possible. The film is very clear and heat-shrinks to a tight fit which gives good clarity and reduces the appearance of having a cheap drop cloth over your window. It comes with doublestick tape. Our usual approach was to buy a cheaper kit for the film (ignoring the tape it came with) and 3M tape for the tape, rather than a 3M kit. YMMV.

You'd be stuck without being able to open the window or adjust that internal shutter for the heating season, but this is a common tradeoff. Installed carefully they don't look too bad, and they cost a lot less than new windows. I did that on nearly every rental in college, as they usually were "renter pays for heat and landlord can't be bothered to fix the leaky windows."

In a more general approach to finding drafts not at windows only, you can have a "blower door test" done to quantify and identify your leaks, or you can just look for places in need of caulking or re-caulking outside and address them.