I've done many kolbe sash kits and it's possible to have them fit tight and square it's just a matter of willing to do the fine details. Making sure it's measured exactly right and/or some times you need to get the rabbet plane out and work on the opening or sash.

But if you can do the pocket window it might be a better option. The only down sides are the cost is much more and you loose a little bit of glass space. You do get the benefits of the cladding though and you have a square window. Just make sure it's insulated and weather sealed properly.

As far as the glass upgrades. If you want that U Factor to go down, go with the 270 Thermal Plus. Like WoW mentioned the 366 cuts down on the SHGC and the U Factor for the 366 thermal plus and 270 thermal plus is .01 difference so you want that SHGC higher with the 270. You'll keep that cold out better while also allowing the warmth of the sun in. Hope that makes sense...

Thanks for the info.

@windowsonwashington - for foaming the weight box, do I just need to fill the hole to access the weight box, or pull the entire channel piece of wood out and fill the entire section with foam or insulation? So my question is, am I ensuring that openings are closed for a draft or fill the entire void? My thought is the void just needs to be sealed, not filled as a void of air as long as it's filled should help insulate.

@Fenestration_Taylor - In your experience what is the markup for the ThermoPlus? Also, no I am leaning back toward sash kits because the local Kolbe rep said he would come out and help do the measurements to ensure they are done right and precise. I am not afraid of doing a little planing and trimming especially since the frames are in good shape and it's all wood. The problem was the last house was all Granite all the way around the window so if you measured on the large side and had to cheat in, there's only so far you could go.

The Therma Plus will probably be somewhere between $50-100 more depending on the size of the unit.

I personally like the sash kits more because I think they look better, it's not a window within a window. It depends really on the house but in general it might be one or two windows on every few jobs that we ever have to fit a window to an opening that is not square.

Sash kits I think are very underutilized. The price isn't too far off of a vinyl window and they look more historically accurate. You just have to be willing to put some paint on them every few years.

You have previous experience with them but just my personal preferences on the sash kits are that the sash have no sash plough and that the jamb liner matches your exterior/interior. No sash plough is more money but I think it looks better (more historically accurate) and beige or white jamb liners are the same price.

Ok, thank you. I have the Kolbe guy coming out tomorrow night and he said they are glad to provide someone to do the precision measurements. I'm leaning toward sash kits now as these windows that I'm replacing are in a lot better shape than the ones I did in the last house and I just think for one we screwed up measuring and there were a lot of weird openings that were very unforgiving.

Thanks again!

Good idea, as a sash pac is only as good as the measuring. When I measured them I used to get funny looks from people as I used an old fashioned Lufkin stick rule with the metal slide rule as the slide rule helped immensely in getting exact dimensions. As well as an angle finder or protractor to make certain the bevel of the bottom rail of the lower sash matched the sill angle. You would really be surprised how much of a difference a couple of degrees the bevel being off will make! Also go for the option of (2) sash locks if it is not standard.

+1

If you feel comfortable measuring them and getting them done right, I also prefer the more accurate look of the sash packs.

In terms of the weight boxes, yes...static air is an insulator. Question becomes how well can you get that air static.

We just drill holes in the jamb behind the sashes and fill them with low expansion foam.

Not the cheapest option but it does the trick.