Replies

1. 
   JWolfe1|Oct 13, 2021 11:37am|#1

   Here is my unscientific take. Andersen didn't put foam in there for a reason. Adding your own will likely cancel any warranty. Even if you do it right the benefits surely won't be transformational and likely barely incremental. In 20 years if you don't ruin the window I'm not sure you'd save enough energy to pay for the foam never mind what is likely to take a ton of time. It sounds like an incredible amount of fidgety work for almost no benefit. Please note that I am not an energy consultant nor have deep knowledge of the ins and outs of window construction.

2. Expert Member
   Zephyr7|Oct 13, 2021 12:35pm|#2

   If the air spaces are small enough, they don’t need foam to perform well in terms of insulating performance. The purpose of foam is to trap air so that it can’t move, the air itself is what is helping to block heat transfer from one side to the other. By keeping the air spaces in the window frame small enough to prevent convection currents, you keep the air still and accomplish the same thing as the foam. If you look around, you’ll find many window frames aren’t filled with foam, but they do have lots of thin dividers to partition the internal space into many small compartments.

   The foam might do something to improve rigidity of the frame, but I doubt it will do much. You’re pretty much sure to void your warranty too. I wouldn’t bother.

   Bill