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#1
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Heat loss through skylight
I have 6 skylights in my house (12 year old house).
In trying to lower my heating bills, I am looking at all possible ideas to save. I have noticed that the rooms with skylights are MUCH cooler than other rooms, making me conclude that heat is being lost through the skylights. How do I minimize this heat loss? |
#2
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Heat loss through skylight
You might get some improvement by adding ceiling fans or a ducted
circulation fan to move the warm air at the ceiling back to near floor level. If your skylights are at the top of a shaft you can close off the shaft at celing level with a plastic panel. The skylight is a window which is less insulated that the ceiling and since warm air rises it is even worse than a standard window. I have seen installations where the skylight is covered with an insulated panel during winter. |
#3
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Heat loss through skylight
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#4
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Heat loss through skylight
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#5
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Heat loss through skylight
My code for ceilings is R 35 mimimun, a single pane glass is R 1, dual
pane lowEargon R 3.3. Seal it up with R 7.2" foamboard glued together for R 30+ for winter, or put it on hinges to open only in daylight, use a rope or some sort of device. Or get fancy and motorise it and use x10 controllers. I use Foamboard the R 7.2" type to seal a few windows and fireplace. On my fireplace I screwed in steel L channel and glued magnetic tape to the foamboard, 3 sheets glued together to seal to the steel L channel, its a removable Plug, it made a big difference in warmth in the living room and furnace cycles less. Skylights are like a hole in your ceiling letting out heat. Since heat rises no glass made is considered energy efficient enough for ceilings in high heat Zones. |
#6
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Heat loss through skylight
m Ransley errs again:
Skylights are like a hole in your ceiling letting out heat. Since heat rises no glass made is considered energy efficient enough for ceilings in high heat Zones. Nonsense. InsUlation only slows heat loss. If each layer of glazing blocks 10% sun and adds R1, the net loss for an N layer skylight on an average Dec day in Chicago is 0.9^Nx460-24h(65-26.7)/N Btu/ft^2, ie any skylight with more than 2 layers will have a net gain, vs a loss for mere insulation. Nick |
#7
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Heat loss through skylight
Nick you are an idiot, there is to little sunshine in winter to give a
net gain, the days are to short, the suns angle to low at Chicago latitudes. I replaced a 6ftx9ft single pane S facing window with Tri pane and insulating curtains, That alone cut my utilities in winter 10 %. You also Assume its always sunny in chicago. |
#9
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Heat loss through skylight
dadiOH wrote:
wrote: I have 6 skylights in my house (12 year old house). In trying to lower my heating bills, I am looking at all possible ideas to save. I have noticed that the rooms with skylights are MUCH cooler than other rooms, making me conclude that heat is being lost through the skylights. How do I minimize this heat loss? Step #1, check to see that you are actually losing heat....climb up to the top and see what the temperature is. On sunny day it will most likely be *way* hotter than your house and you are gaining; probably will lose at night. Maybe they'll balance each other out. The highest point will always be the hottest, no? The skylight loses heat all of the time. The room will gain some heat during the day, dependent on orientation and weather, due to solar gain. It's possible that the solar gain may outweigh the heat loss, but unless there's some heat storage mechanism, and the skylit rooms have their own thermostats, the room temperature will fluctuate between too hot and too cold. Adding another gasketed pane of glass or plastic to seal off the bottom of the skylight or skylight shaft will go a long way to help minimize heat loss. Ceiling fans will help mix the air and help keep the heat more evenly distributed throught the height of the room - it will keep more heat where people live - 6' and lower. On the flip side, a retractable awning/shade will help keep some of the excess solar gain from warming the room and its contents during the summer. R |
#10
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Heat loss through skylight
wrote in message I have noticed that the rooms with skylights are MUCH cooler than other rooms, making me conclude that heat is being lost through the skylights. It could also be that those rooms just don't get as much heat anyway. While your conclusion may or may not be correct, the reasoning is wrong. If the skylights don't have some sort of double pane or storm panel, add one. Watch for excessive heat buildup though, when the sun shines |
#11
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Heat loss through skylight
wrote in message oups.com... I have 6 skylights in my house (12 year old house). In trying to lower my heating bills, I am looking at all possible ideas to save. I have noticed that the rooms with skylights are MUCH cooler than other rooms, making me conclude that heat is being lost through the skylights. How do I minimize this heat loss? Why is there air? Since you provide absolutely no information on your construction/type of skylights and climate, I refer you back to my questions. |
#12
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Heat loss through skylight
SQLit wrote: wrote in message oups.com... I have 6 skylights in my house (12 year old house). In trying to lower my heating bills, I am looking at all possible ideas to save. I have noticed that the rooms with skylights are MUCH cooler than other rooms, making me conclude that heat is being lost through the skylights. How do I minimize this heat loss? Why is there air? Since you provide absolutely no information on your construction/type of skylights and climate, I refer you back to my questions. Sorry...here are some details: The skylights are flat (not the bubble type). The brand, I believe, is Velux. I live in Chicago. I have thought about getting plexiglass installed to the inside frame but now concerned that it may not be a good idea since during summer, the 'pocket' between the plexiglass and the skylight might get too hot. |
#13
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Heat loss through skylight
I just installed a sheet of tempered glass in a clients skylight. Her's
is more like 85 years old. Built like those old casement windows. As soon as we dropped it in place you could feel the draft stop. The air shaft to this one was more like 5-6' deep. It was in Evanston, by the way. You could also use polycarbonate or that multi channel stuff they use for greenhouses. That would certainly take any temperature you could throw at it. Richard |
#14
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Heat loss through skylight
Velux is the leading and quality brand of skylights. Ones that are 12
years old should be reasonably energy efficient, provided they are still intact and have not loss the seal between panes. I agree with those that have said the skylights may not be your problem. There are lots of other factors at work. How the heating systems is set up and balanced is one. Another is any other differences in rooms. For example, skylights are often used in rooms with cathedral ceilings. Those areas take more heat because of the high ceiling, plus frequently these ceilings have less insulation than one with an attic. I have two good size Velux in my family room and don't have any problem with the room being colder. Plus, you have to balance what you are achieving. If you save some energy by putting up something more to shield the windows and it looks like hell or blocks the light, is it worth it? |
#15
Posted to alt.home.repair,alt.solar.thermal
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Heat loss through skylight
wrote:
I have noticed that the rooms with skylights are MUCH cooler than other rooms, making me conclude that heat is being lost through the skylights. How do I minimize this heat loss? The skylights are flat (not the bubble type)... I live in Chicago. December is the worst-case month for solar house heating in Chicago, when 460 Btu/ft^2 falls on the ground and 740 falls on a south wall on an average 26.6 F day with a 34.0 daily max, so 1 ft^2 of single of R1 horizontal glazing with 90% transmission would gain 414 Btu and lose 24h(65-26.6)1ft^2/R1 = 922 for a net loss of 508 Btu per day. I have thought about getting plexiglass installed to the inside frame Good idea. That might reduce the gain to 373 and reduce the loss to 461 for a net loss of 88 vs 508. but now concerned that it may not be a good idea since during summer, the 'pocket' between the plexiglass and the skylight might get too hot. In full sun (say 250 Btu/h-ft^2) in Chicago, 225 might pass through the first glazing and 203 might pass through the second, a difference of 22. If it's 83.7 F indoors and outdoors (the average daily max in July), R1 resistors to that indoor and outdoor temp might make the temp between the glazings 83.7+22xR0.5 = 94.7 F, which seems OK. I once made a hinged Styrofoam shutter for a west-facing skylight with a 1:1 slope and several layers of glazing and painted the skylight side black to make it warmer in wintertime, if the shutter were closed most of the time. It was, but after the dead of winter, the Styrofoam melted into a black mountain range with pink crevasses and peaks around the screws that held the foam to the plywood backing. It got nice reviews in an art show :-) An R2 skylight might collect 0.81x1940 = 1571 Btu/ft^2 of unwelcome solar heat on an average July day in Chicago. A reflector hinged at the north edge of the glazing might eliminate most of that and enhance winter collection. Sun elevations in Chicago (N lat 41.8) are 90-41.8+/-23.5 = 71.7 and 24.8 degrees above the horizon at noon on 12/21 and 6/21, so the upper edge of a reflector can block all the direct noon summer sun if it's on a 71.7 degree elevation line up from the south edge of the glazing, like this, viewed in a fixed font: . - - - . . | -- north 1.5' . . 1.12' . . | . . 48.2 degrees 71.7 degrees ............----------------------.................. 1' If the glazing is 1' wide in the north-south direction, we can bounce all the noon winter sun into it if the reflector edge has a 90-41.8 = 41.2 degree elevation angle from the north edge of the glazing, which makes the upper edge 1tan(48.2) = 1.12' above the south glazing edge, with a sqrt(1+1.12^2) = 1.5' slant height, so 1 ft^2 of skylight would collect about 0.9x0.81x740 = 539 Btu and lose 461, for a net gain of 79 Btu/ft^2 per day. If we replace the skylight glazing with hinged R10 foil-foamboard and use 1.12' of R1 vertical glazing and raise the board up to 48.2 degrees during the day, we might collect 0.9x0.9x740 = 599 Btu and lose 6h(70-30)1.12ft^2/R1 = 269 during the day and 18h(65-26.7)1ft^2/R10 = 69 at night, for a net gain of 261Btu/ft^2 per day. If we leave the R2 glazing in place and use 1.12' of R1 vertical glazing, we might collect 482 Btu and lose about 6h(70-30)1ft^2/R3 = 80 during the day and 57 at night, for a net gain of 344. Nick |
#16
Posted to alt.home.repair,alt.solar.thermal
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Heat loss through skylight
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#17
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Heat loss through skylight
wrote in message oups.com... SQLit wrote: wrote in message oups.com... I have 6 skylights in my house (12 year old house). In trying to lower my heating bills, I am looking at all possible ideas to save. I have noticed that the rooms with skylights are MUCH cooler than other rooms, making me conclude that heat is being lost through the skylights. How do I minimize this heat loss? Why is there air? Since you provide absolutely no information on your construction/type of skylights and climate, I refer you back to my questions. Sorry...here are some details: The skylights are flat (not the bubble type). The brand, I believe, is Velux. I live in Chicago. I have thought about getting plexiglass installed to the inside frame but now concerned that it may not be a good idea since during summer, the 'pocket' between the plexiglass and the skylight might get too hot. Have you considered your idea as seasonal? Plexi or plastic will warp and absorb a lot of light. A lot cheaper for one season UV light eats the plastics over time and they will turn yellowish. |
#18
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Heat loss through skylight
I have 2 baths with Velox Lo E skylights
(about 4 square feet each) and motorized vent flaps (no windows in either). I haven't noticed any "cooler" problems as long as the vent is closed. These 2 baths are not that big. However, even if open, the air tends to go out, so it may produce a draft of moving air, but not cold outside air. I also have 2 of these same units in the kitchen, however, as the kitchen is open to 3 other rooms, I probably wouldn't notice. BTW, also in the Chicago Burbs. SQLit wrote: wrote in message oups.com... SQLit wrote: wrote in message egroups.com... I have 6 skylights in my house (12 year old house). In trying to lower my heating bills, I am looking at all possible ideas to save. I have noticed that the rooms with skylights are MUCH cooler than other rooms, making me conclude that heat is being lost through the skylights. How do I minimize this heat loss? Why is there air? Since you provide absolutely no information on your construction/type of skylights and climate, I refer you back to my questions. Sorry...here are some details: The skylights are flat (not the bubble type). The brand, I believe, is Velux. I live in Chicago. I have thought about getting plexiglass installed to the inside frame but now concerned that it may not be a good idea since during summer, the 'pocket' between the plexiglass and the skylight might get too hot. Have you considered your idea as seasonal? Plexi or plastic will warp and absorb a lot of light. A lot cheaper for one season UV light eats the plastics over time and they will turn yellowish. |
#19
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Heat loss through skylight
Hi Art,
You said you have "motorized vent flaps" on your skylights. Did you get these installed (as an addition)? If so, where can I buy them? Would appreciate a contact number for the company where you bought them from and also the installer. I called Velux and they said they have retractable shutters (motorized or non-motorized, but basically to block sunshine). Are the "motorized vent flaps" same as the retractable shutters? I am thinking of having Velux installed retractable shutters as the two skylights in the vaulted family room bring in sun directly on to my TV, making it almost impossible to see anything on the screen (during non-winter months). TIA. Art Todesco wrote: I have 2 baths with Velox Lo E skylights (about 4 square feet each) and motorized vent flaps (no windows in either). I haven't noticed any "cooler" problems as long as the vent is closed. These 2 baths are not that big. However, even if open, the air tends to go out, so it may produce a draft of moving air, but not cold outside air. I also have 2 of these same units in the kitchen, however, as the kitchen is open to 3 other rooms, I probably wouldn't notice. BTW, also in the Chicago Burbs. SQLit wrote: wrote in message oups.com... SQLit wrote: wrote in message egroups.com... I have 6 skylights in my house (12 year old house). In trying to lower my heating bills, I am looking at all possible ideas to save. I have noticed that the rooms with skylights are MUCH cooler than other rooms, making me conclude that heat is being lost through the skylights. How do I minimize this heat loss? Why is there air? Since you provide absolutely no information on your construction/type of skylights and climate, I refer you back to my questions. Sorry...here are some details: The skylights are flat (not the bubble type). The brand, I believe, is Velux. I live in Chicago. I have thought about getting plexiglass installed to the inside frame but now concerned that it may not be a good idea since during summer, the 'pocket' between the plexiglass and the skylight might get too hot. Have you considered your idea as seasonal? Plexi or plastic will warp and absorb a lot of light. A lot cheaper for one season UV light eats the plastics over time and they will turn yellowish. |
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