This is great, thanks! The whole house fan is a fantastic idea for our area. I visited the Serious window dealer today to get a quote. I also have quotes from Kolbe and Marvin and will make sure to compare apples to apples where I'm aiming for a lower U-value and a higher SHGC. Of course price will be a consideration as well as aesthetics, but what I really took out of this discussion that I think will prove very beneficial is that for our climate while it might be better to aim for a higher SHGC, we may be OK with something middle of the road (which might overall be less expensive). We are trying hard to get as energy efficient as possible, but also have to consider how this integrates with the rest of the (old) house. The whole house fan is a great idea since we don't have a/c. We were considering mini-splits for one part of the house, but it might not be necessary if we have a whole house fan. If I can, I will update you on prices/quotes once I get everything. Still, any thoughts on Fiberglass vs. Aluminum clad for our area? Marvin has a fiberglass window option too. Thank you, thank you!

Single pane, aluminum: 18.7 MillionBtu, $171.52
Serious, U=0.19, SHGC=0.22: 11.5 MillionBtu, $105.26
Pella, U=0.31, SHGC=0.54: 7.0 MillionBtu, $64.58

Note that in all cases if you have unblocked solar radiation, the south-facing windows provide a net gain, NOT a net loss of energy, so you are wise to consider high SHGC windows. In the case of the Serious and Pella windows, the south, east, and west windows are all predicted to provide net energy gains, not losses. The RESFEN results suggest that there is no reason to mix and match high and low SHGC windows in your climate if you have solar radiation available. Since the solar radiation is irregular, you could choose to mix and match. In my house, I have both, and I cannot see any difference in the appearance.

The RESFEN results suggest that the heating costs associated with the windows are not that great, so I would not worry too long and hard about window selection. Just don't overspend on windows since there is not that much gain to be had. Those costs presented above will appear low relative to your actual costs because the house modeled is modest in size and very well insulated, and the costs do not include natural gas monthly connection fees.

Lee Dodge -

I agree with most of what you are saying but I disagree that one should try and get the highest SHG window possible for the OP's climate. He is already getting baked out of his house now, in winter, with the current old windows. If he places high SHGC windows and the BTU's skyrocket, he will end up posting the following comments like the people below have.

Overheating a home is very possible in a passive solar home, even in wintertime. The OP's climate is not northern arctic Canada. According to NOAA it is a very moderate winter climate. When the OP gets very high SHG windows and then gets baked out of his home during 3 seasons; winter, spring, and fall. It becomes a failed passive home design. Some home owners have utilized RESFEN and other similar programs and have experienced overheating issues during one or more seasons. However the RESEFEN program algorithms were entered, I would confidently state that it is  NOT 100% error free in its recommendations. There is a margin of error and maybe that would be a important number to find out. 

Posted By ecobuilder on 26 Nov 2009 12:09 AM
 The newest version of the windows have a shading mechanism as part of the window to control the overheating issues that happen in most solar homes. Passive solar works great but controlling it has always been the issue.

Tom Pittsley
[email protected]
www.eebt.org

Posted By egouin on 17 Nov 2009 07:56 AM

One other thing to consider is - when - you are going to get BTUs coming in from the South facing glass. It is entirely possible to overheat during the day in the dead of winter.

Posted By dmaceld on 16 Nov 2009 12:13 AM

I don't know what the passive house guru's say, but based on my experience with my ICF house don't shortchange the window shading issue. I have good shade in the summer, and pretty good sunlight in the winter, but the fall and spring are a different matter. In those two seasons we have enough solar heat gain coupled with warm outdoor temperatures that our AC load is just as heavy, or heavier, than in the summer.

I agree that if you want to utilize passive solar heating, that you need a strategy for shading when you need to limit solar heating. Seasonally, you can use overhangs on the south side (more effective in dry climates with intense sun than in places with higher humidity and haze) and deciduous trees. On a daily or hourly basis, interior or exterior shades that are reasonably reflective due to light surfaces are very useful. If you plan to avoid air conditioning by trapping cool nighttime air, then you better pay attention to the weather forecast, and use that to determine the level of night chilling required. This requires an active house owner, not a passive one. High solar gain windows on the east and west sides are an advantage in my climate, but require more active intervention to avoid overheating.

Concerning the weather in the San Francisco area, it was Mark Twain who said, "The coldest winter I ever saw was the summer I spent in San Francisco." Failing to remember his observation, I have a number of sweatshirts in my closest emblazoned with San Francisco street cars that were required from summer tourist trips there with poor wardrobe planning.

Yes, love the Mark Twain quote and I try to remind summertime visitors to dress warmly to avoid having to purchase sweatshirts! We avoid SF during the summers. We are far enough South of the city on the peninsula that we don't get the fog and the summer days are usually quite nice with only a few weeks where you might want aircon. The nights however, are always cool (I've rarely seen it above 68) no matter how hot it gets during the day which is why the whole house fan is a great idea. Right now with our leaky, single pane window set up, when it gets to those rare 90F days we are fine for a day or two, but when it's 3 days in a row or more we are miserable. The house just can't expel the heat even with the windows wide open at night, closed and curtains pulled during the day.