Last week a visitor to my site asked me about the best way to insulate around a replacement window. A few days later I got the same question so I decided to compile my response into an article below.
There are two main types of insulation are used when insulating around replacement window. Many contractors use fiberglass. There is spray foam that gives the highest R value; this is one of the best insulation you can use around a replacement window.
Fiberglass usually ends up not giving much insulation because it is put in to thick, or it is put in to thin and either way does not give proper air flow.
Air leaks may be present around replacement windows even if they seem to be working properly. The air leaks might be caused by not having enough insulation between the interior and the window frame.
What you need to do here is to take the trim off of the window carefully using a large putty knife – this will expose the frame. Then fill in the gaps in insulation with foam, which will seal around the window.
You can buy a kit from your home improvement center to do this with or order one from the internet, however, make sure the foam is for around windows. Foams made of HFC or propane propellants are excellent choices; do not use one that has bleach in it. If you are using expanding foam make sure you do not overdo it or you can be in real trouble if it expands too much. Replace trim.
If you are insulating the replacement window from scratch, put your fiberglass around it and then spray it with the spray foam. In my view this is the best way to insulate around a replacement window. However do take the time to check out some other reliable sources online.