ericjeeper
Addicted to ArboristSite
I believe some utilities will also give you a break on your electric bill as well. Mass Electric used to, not sure if they still do since being swallowed by National Grid.
I love the idea of passive solar... probably not the kind you mean... just big arse south, east and west facing windows.
Unfortunately, and hopefully without getting too political here, the $1500 tax credit, which one can get for replacement windows, stipulates a solar heat gain coefficient of 0.30 or less... no matter where you are in the country. A low SHGC is great if you spend the majority of the time cooling. Unfortunately, for this small part of the country (y'know, the entire northern half) the primary heats and doesn't even have AC, save for maybe a window unit... maximizing SHGC while minimizing U-factor makes the most sense. Looks like I'll be getting my $1500 on the new boiler, and not on windows.
Unfortunately The SHGC and the U factor run sort of hand in hand.
It usually takes two layers of Double lo-e to achieve a low number.
But here is my take on solar heat gain.. Ok lets say that clear southern facing window lets in 100,000 btus during the six hours of sun that shine on it.. We still have 18 hours when the sun is not hitting it..Then if it is just a clear non insulated glass pack it will possibly dump out many times more than it collected.
A prime example is my hydronic solar collectors. I can force them to run 24 hours a day. So during the sunny part of the day they will bring my six hundred gallon tank up to 140 degrees.Now if I let the pump run round the clock. It will dump all that stored energy back out the panels.
So the best possible scenario for a window is a clear pack during the sunny part of the day, Then all the sudden its features change to an insulated glass pack. LOL Which for now is impossible..
So we have to pick our battles.. And I choose to forfeit a big solar gain and opt for a higher insulation value.
I have radiant heat in my slab. My bedroom has 2 double hungs facing south. with lo e and argon.the numbers on them are roughly u factor of .34 and SHGC of 35 They kind of screw me with my heat type. They will let a fair amount of sunshine/heat in during a few hours of the day., So that satisfies my thermostat in the bedroom. (Which in turn will turn off the floor loop.). Ok now evening settles in the heat which came in the double hungs will slowly go back out and the loop will come on and try to play catch up.
I have one other window in that room.an inline slider it is 67 inches wide and 48 tall. with a triple with krypton and double soft coat lo e.At night at 15 degrees exterior temps. The two different glass types will vary on inside surface temps as much as 8 degrees.Of course the triple with krypton is the warmest. The numbers on it is . u factor .18 SHGC is .26
I only have 4 windows left in the house to replace with triple with Krypton.I plan to replace these four this summer. (My house is not even 5 years old yet.)Will the triple ever pay for itself? Maybe not in actual dollars but for sure in comfort. My office window is double with argon. And My chair is less than 3 feet from it.. when it is cold outside I can barely stand to sit here.The cold just radiates through it to the point it feels like cold air rushing in.Yet it is virtually air tight. Ok if this makes any sense at all..