Let the sunshine in?

October 23, 2007 7:05 AM

Is there a way of determining how much heat I am losing by opening versus closing the shutters of a drafty window? And also, determining how much heat I am gaining when the sunlight streams in through the open shutters?

I have very very drafty old windows. I also have very effective wooden shutters. In the winter, I put one of those Saran-wrap looking plastic sheeting on the windows and keep the wooden shutters shut, to keep the cold out. But I really hate how dark the house gets, and all my houseplants die within days due to the lack of sun. The windows, when I keep the shutters open, let in an enormous amount of sun. In the summer, just a few hours of open shutters will render the room boiling hot. Is there any way of measuring how much heat I am losing if I keep the shutters open during the day, and also, how much heat (if any) I gain by letting the sun in?

posted by jujube to Home & Garden (4 answers total)

There are tons of resources for calculating solar gain from windows. Here's a basic rule of thumb:
east/west/north facing windows should be CLOSED and BATTENED DOWN in the winter.
South facing windows should have shades OPEN, shutters OPEN, for the longest possible amount of time during daylight hours. At night, shades should be drawn over these windows to keep heat in the room.

I'm on the wrong computer to give you tons of links right now, but Southface is a good jumping off point.

Basically, any window that lets in sunshine during daylight hours should be allowed to do so, especially if you've got plastic lining over the insides. All windows should have heavy shades drawn @ night. The test is to stand in front of the window with the sunshine glaring in, if you get warm pretty fast, you need that sunshine.
posted by TomMelee at 7:19 AM on October 23, 2007

The short answer is yes, there is a way, but it is likely to be complicated. It may be easier to get a thermometer and try it out -- windows/shutters open versus not, and so forth, since I believe this is what you really want to know, in the end.

The long answer involves radiative heat transfer (heat transfer from the sun) versus convective heat transfer. (See, for example heat transfer)
posted by Comrade_robot at 7:23 AM on October 23, 2007

Response by poster: Thanks TomMelee--but what about southwest exposure?
posted by jujube at 7:29 AM on October 23, 2007

Stand in front of the window in the morning and afternoon if possible. If you're only getting an hour or two of solar gain through it, it's not worth the loss the rest of the day to leave it open. If you get good warmth through it all day, leave it open. Here's a source, but it's a crappy one:
http://www.jc-solarhomes.com/shows/ste/ste.htm

That'll let you know what you can expect in terms of gain based on latitude. Somewhere, there's this great chart from the government about exactly what peak times and directions and latitudes get what in terms of gain.

Sorry I'm not more help.
posted by TomMelee at 8:52 AM on October 23, 2007