Based on your descriptions i would opt for the 366 glass.

using 366 is going to do a better job protecting your furniture and such from fading than will 272, plus it will do a much better job of keeping your rooms more comfortable in summer, and it will match the glass color of your other windows.

You will get less solar heat in winter, and there are times when the sun is shining bright, but you aren’t feeling it through your windows, that you might wish that you had gone with 272, but realistically the actual advantage of high solar gain in winter is more about ”feels so good” than actually offering a significant performance advantage in most cases.

Last sentence pushes you to the 366 camp for me.

I would get a sample and look at it to see if you like it.

Another option would be Triple. Best of both worlds.

@oberon476, "feels so good is interesting". Are you saying its more about how the sun feels on you vs the actual "heating effect" like a furnace warming the air?

To clarify as well, this part of the home is a mixture of these doorwalls , and a few other older pella windows and some weatherguard put in at the same time in the walkout where one of the door walls (1 of 3). So downstairs the older weatherguard will stay with the existing glass. Does it make sense to go 272 down there since its got a lot of protection and the other windows wont be changing? I am probably splitting hairs here.

Also clarification, when I say "i dont mind a bit of increased heating cost", im unsure how much it will be different, will it be 10 percent, 20, 30. my peak heating bill for both sections of the house, 2 furnaces and 2750 above ground and an 800 walk out is about 200 at peak heating season.

There are days when I have a sunny day in say Feb that I'm in my office, the heat is coming in and my darn toes are still freezing from the drafts. I'm really hoping, that this will get better with the new door walls as the old ones are leaky, poorly installed, bad seals and dont seem to have foam around them. I think the air sealing will be much better once installed properly. However, there could always be quite a bit of air coming in from the rim joists (its just 2x12 set into cinder block walls that have no insulation). If its still trouble some , i guess i could tackle that job next trying to cut drywall (basement is fully finished) and seal those up but I"m hoping the new doors help a lot.

What i don't want is to still be uncomfortable and have another 100 dollars on my heating bill. But as I sit in my office on this nice 55 degree michigan day, I have to have the sldiing door cracked a bit to let cool air in so the office doesn't over heat. The living room isnt so bad because the area is much greater. Based on the area I have a total of 138 sq feet of doors (80" x12 ft in the living room and 80' by 9 feet in the office )facing south in an 800 sq foot section of the home combined. However, my small office has a bit over a 1/3 of that 138 sq ft of glass but the room is probably 12x10.

When we have a sunny day in the winter, the furnace often doesn't run once it is heated up in the am. I hate to lose that, but again, comfort rules.

Are you saying its more about how the sun feels on you vs the actual "heating effect" like a furnace warming the air?

Yep, that's exactly what I am suggesting. Back in the 70s (some 60s and 80s and even to today too), everyone who was interested in super great free energy performance in new homes was all over solar. It was the low hanging fruit that everyone who fancied green building and free energy was reaching for. Unfortunately the reality was that in the vast majority cases it simply didn't work well enough to justify the hype or the expense. Solar gain through windows in winter is awesome, I love it and encourage in the right circumstances with the understanding that far more than not, it is the warm fuzzy feeling that you are gaining, not the free money in energy savings.

In summer direct solar heat gain turns rooms facing south or west (especially west) into ovens, as you commented in your post. In winter you can get a very nice free heat gain when the sun is shining directly on the window glass, but when it's not shining directly on the window then any potential free heat isn't happening. What is happening is that all that free heat is heading back out the window to the outside when the sun isn't shining directly on the glass.

You can certainly see some energy performance advantages along with the feels-really-good warm fuzzy on bright sunny winter days, but not so much at night, or when it's cloudy, or when the sun is at oblique angles to the window....

From a solar heat gain perspective, 366 is the better choice in summer and 272 is a little better in winter. Spring and fall are kind of a wash. Per U-factor performance, they are pretty close, 366 is a little better than 272, but they are so close that I wouldn't worry over that one. IF your windows are well shaded in summer and you are in a northern environment, then I would absolutely suggest 272 for the solar gain advantage, but as soon as you said that your room was like an oven in summer, then 366 is the proper choice for energy performance and comfort.

IF you have a house that's designed specifically to take advantage of winter solar heat gain, such as some net zero or passive house designs, then you might be able to harvest that solar heat, if not then ultimately it's more than likely to be a net loser over a full year.

It really does feel good for a few cold months of the year when in the right conditions, but not so much other times when not.

Finally, which ever one you choose will be an upgrade over what you have now. And I also agree with WoW, that triple pane could be an option for your situation.

Is it worth going to 272 on the basement slider thats protected by the deck? Or keep the 2 upstairs sliders and basement 366 for consistency sake?

+1 to all of the great advice above. Based on your summer experience, it sounds like 366 is the better choice of these two, although given your cold climate, triple pane would be ideal IMO. You'd get virtually the same solar gain with reduced energy loss and better overall efficiency. Your home would be most comfortable and save the most on heating/cooling, its a win-win.

Regarding a basement window under a deck, presumably there's really no solar gain consideration for that window so I'd choose the best U value there that is within your budget.

What they said. In Michigan, don't see an application where triple isn't a win-win.

Triples are an interesting topic. For the price incurase , 30-50 percent are they really worth it? I"ve talked to 3 different companies and none have recommended them.

At 50%...no. At 30%, for a 30% improvement in efficiency...makes a bit more sense.

We try to get folks into triple pane as much as possible so we mostly charge the differential in materials cost with nominal mark ups. In our model, it amounts to a 12-15% adder over the standard window. In that case, the math definitley makes sense.

So am I understanding Triple with 366 is what you are suggesting if I go to Triple? On the Anderson 200 NL doors the increase was much more than 12-15 percent if i remember correctly over the double pane 366 and the U values not much better.

@dsiggi

No. Triple with Low-e 272.