Say you want a door but you also want to use it for solar gain. Is there a type of door style/material/size thats best?
Lisa_Tom
| Posted in Green Products and Materials on
I can’t seem to get values for doors from manufacturers or when I do, the SHGC drops precipitously once you put the glazing in the door, e.g., Sungate 500 SHGC drops from .6 to less than .4 when put in a swinging fiberglass patio door. Of course glass size is limited to about 2 ft width, although the length is long. How I get what I need in SHGC in a south facing door. Do I change door style, size of door/glass, material, glazing brand, ? etc. Thanks
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Lisa,
If you specify double glazing, the highest SHGC glazing option is probably clear double glazing. Of course, clear double glazing has a downside -- it loses more heat at night than low-e glazing.
That's why most people compromise, and choose high-SHGC glazing with a relatively low U-factor. (Assuming, of course, they you want high solar gain.) That usually means double glazing with a hard-coat low-e coating and argon fill, but there are many options.
Most U.S. door manufacturers are ignorant about glazing. You might want to order your door from Thermotech Fiberglass in Canada; the company is knowledgeable about glazing options. Here is a relevant web page: Thermotech Fiberglass doors.
Sungate 500 is low E, high SHGC but for some reason Milgard is lowering the SHGC values considerably when they put it in one of their patio doors (NOT the u value which is going a little bit up). I'm in San Diego so its a little bit more flexible. Thermotech would be too expensive for shipping and anyway I don't need their triple glazing for San Diego. The Thermotech people also don't understand why the SHGC value would drop so low. Who comes up with these whole door whole window values anyway. Are they ever accurate?
Lisa,
The NFRC rating method requires door manufacturers to give a whole-door SHGC number. The number is not based on the area of the glazing; it is based on the area of the door and frame. Therefore the opaque materials (the stiles and rails of the door) take up a significant percentage of the door's area, and significantly reduce the whole-door SHGC.
So.......is the door useless for solar gain?
Lisa,
No, a door is not useless for solar gain. It depends on the door. Look at the photo: the door on the left will allow more solar gain than the door on the right.
.