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?

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.

wrote:

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.

Hi,
In my last house I had 4 huge sky lights in the loft. It was a kind of
bubbly looking double pane one with lots of air gap in between. I
definitely thought I was gaining heat into the room rather than losing
it in sunny days. You can install shutter I guess.
Tony

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.

--
dadiOH
____________________________

dadiOH's dandies v3.06...
....a help file of info about MP3s, recording from
LP/cassette and tips & tricks on this and that.
Get it at http://mysite.verizon.net/xico

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

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

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.

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.

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

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

In article . com,
wrote:

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.

Yes, moveable insulation is the answer.
I saw a Book just on this.

--
Impeach Bush ! a noble cause
Operation Iraqi Liberation = O.I.L.

wrote:
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.

Snipped the rest.

Your reference to R1 and R2 skylights and glazing may or may not have
been understood. You should indicate how those designations correspond
to a typical skylight.

That homemade skylight shutter that had the foam that melted - what was
the purpose of painting the top side of the insulating foam black to
gain heat? That's just going to absorb the heat and raise the heat
inside the foam - pretty much exactly the opposite of what should be
done. The melted plastic is also a safety issue - it releases dioxins.
The foam itself is required by code to be covered by 1/2" drywall, or
equivalent, for reasons of fire safety.

It's also a little drastic to totally block skylights when the added
light and skyview is the reason the skylight was installed in the first
place. You're just trying to block the heat flow, not necessarily the
visible light.

R

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?

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.

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.

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.

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.

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

The Velux units I have are about 26" x
~24". They fits between a 24" on-center
roof truss. They came with a small
hinged wood flap at the top, which can be
operated by cords or by a "stick with a
hook." Check out
http://www.veluxusa.com/products/sky...dWithVentFlap/
They offered an optional motor and
controller to open and close the flap.
When I bought the last 2 of them, they
were about $80 or $90 each. The
controller was very pricey (~$200), so I
engineered my own. The motors run
on DC, one polarity to open and one to
close. They have built-in limit switches.
I used a transformer with a full wave
rectifier. A rocker switch applies the
+ DC
in one position and - DC in the other.
BTW, the last ones were purchased
about 8 - 10 years ago. I couldn't find
the motors on their website, but maybe
I just didn't dig far enough.

wrote:
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
egroups.com...


SQLit wrote:


wrote in message
glegroups.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.

On 25 Dec 2005 10:11:52 -0800, 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?

Maybe you should look for another source of heat loss?

I have two (velux) skylights and one 3050 window in my upstairs
office. The room next to it is a bedroom and has no skylights but two
3050 windows. The glass area is about the same. The heat pump duct
area supplying the rooms is the same. The area and volume of the
rooms are the same.

The room with the skylights stays about 4-5 degrees warmer year round.
My conclusion is that I'm picking up enough sun load to offset any
heat loss caused by the glass area in the skylights. I live in the
mid south, but sunload is sunload on a relative basis.

In the winter that 4-5 degrees is ok. In the summer when it can get
to 85F in that room (with AC) we shade the skylights to lower the
temp and help out the AC.

Frank

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.

m Ransley errs again:

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.

You are wrong on all counts. Try numbers :-)

Nick

Nick you are wrong on all accounts try experiance with windows. Your
numbers dont account for real life weather.

If what you stated was in fact true it would be the single biggest
selling point manufacturers of skylights could wish for. So look for
your self, find the claims and post all the net energy gains from
manufacturers of Chicago lattitude. You can`t because they don`t exist.
Your numbers and theory are flawed. I see neighbors go to double pane,
and many more remove them. Skylights cost energy in the real world. You
are like a bad computer program.

m Ransley errs again:

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... You also Assume its always sunny in chicago.

You are wrong on all counts. Try numbers :-)

One more time: 460 Btu/ft^2 of sun falls on the ground on an average 26.7 F
December day in Chicago. Unlike insulation, any skylight with more than 2
layers of glazing will gain more solar heat than it loses... 6 is optimal:

20 FOR N=1 TO 8'layers of glazing
30 GAIN=460*.9^N-24*(65-26.7)/N'Btu-ft^2-day
40 PRINT 100+N;"'";GAIN
50 NEXT

layers net gain

1 -505.2 Btu/ft^2-day
2 -87
3 28.93997
4 72.00598
5 87.78537
6 91.26282
7 88.70224
8 83.11487

A skylight with a south tilt or a shutter or a reflector can gain more.

Insulation can only LOSE heat.

Nick

m Ransley Dec 27, 4:20 pm

"Skylights cost energy in the real world. You are like a bad computer
program. "

So does any window and last time I checked most houses have lots of
those. I'm unconvinced that a skylight is so much worse than a
similar size double pane window in a wall. Both have inside air
against the glass, don't they? Sure, the air may be a few degrees
warmer at the ceiling surface than at a window located in a wall, but
in the big picture, I don't think it amounts to much.

Today and this time of year 6 hr of radiant energy from the sun is all
you get, if it isnt cloudy out. 18 hrs is your time frame to loose
energy, 3 times the period of gain. A dual pane lowEargon window is no
better than R 3.5. Minimum chicago code is R 35 ceilings R 60 being
optimal. Heat rises and is proportionatly lost at a greater rate through
the ceiling than walls. I still say if your numbers reflected real world
weather you would see. Cloudy days are not in your numbers. If what you
said was true it would be a true selling point manufacturers would take
advantage of. But R 3.5 looses heat when there is no sun, and more than
it gains over 18 hrs darkness . Now you show me an R 35 skylight, that
will save energy, but we have no such glass yet.

m Ransley errs again:

Today and this time of year 6 hr of radiant energy from the sun is all
you get, if it isnt cloudy out. 18 hrs is your time frame to loose
energy, 3 times the period of gain.

Irrelevant. Simple physics and real weather data say a skylight with N
glazing layers will gain 460x0.9^N Btu/ft^2 and lose 24h(65-26.7)/N on
an average December day in Chicago. With more physics or calculus, you
might figure dGain/dN = 0 makes N = e^(0.505N+1.47). N = 5 on the right
makes N = 5.6 on the left, then 5.77, 5.82, and 5.84, so N = 6 maximizes
the net gain, vs a ***LOSS*** for mere insulation.

I still say if your numbers reflected real world weather you would see.

Those numbers are NREL's 30-year measured weather data for Chicago.

Why not give up your excellent imitation of a nitwit? :-)

Nick

"m Ransley Dec 27, 5:43 pm

Heat rises and is proportionatly lost at a greater rate through
the ceiling than walls."

So let's say the air temp near the ceiling is 75 deg and it's 70 in the
middle of the room where the windows are. If it's 20 degrees outside,
the temp differential at the skylight is 75-20=55 deg and at the side
windows it's 70-20=50 deg. So assuming the construction and size of
the windows is the same, the skylight will be losing about 10% more
heat than the side window. Hardly anything to get your shorts in a
knot over or worrying about doing anything special as opposed to any
other window.

Is it 10% more, optimal wall insulation is well below ceiling ratings,
from what I have read at different sites even SIP construction by near
50%. Alot is construction techniques but still retings are much lower
in walls.I know it doesnt mean 50% goes up and out, but heat rises, and
it could. Ive never read or seen skylights in optimaly insulated or
solar designs. If it could automaticly close with a foam insulating plug
when shaded it could be a net gain.

"m Ransley Dec 27, 8:58 p

Is it 10% more, optimal wall insulation is well below ceiling ratings,
from what I have read at different sites even SIP construction by near
50%. Alot is construction techniques but still retings are much lower
in walls."

Here's a good link that has some real data:

http://homeenergy.org/archive/hem.di...93/931109.html

It looks like a skylight has roughly 2X the heat loss of a similar
vertical window, so you are right. They also explain why. It seems
the main effect is that with a skylight being installed close to flat,
the gas between panes circulates bottom to top, carrying heat from the
inner pane to the outer. With a vertical window, the gas between panes
doesn't move directly from pane to pane, so less energy is transferred.
Kind of strange, as I would think that would be a second order kind
of effect, but apparently it makes a big difference.

I'm sure there is some heat gain from the sun during winter that helps
offset some of this. It might even offset all of the difference in
some climates. Of course in the summer you have the opposite effect,
where now the heat is working against you. Still, if the differential
is 2X, it's still not all that bad.

m Ransley wrote:


If it could automaticly close with a foam insulating plug when shaded
it could be a net gain.

That's better, but any skylight is a net gain if more solar energy enters
during a day than heat energy leaves during a day, which can happen with
several layers of glazing. For instance, 3 layers of R1 glazing with 90%
solar transmission would gain 0.9x0.9x0.9x460 = 335 Btu/ft^2 and lose
24h(65-26.7)1ft^2/R3 = 306, for a net gain of 29 Btu/ft^2 on an average
December day in Chicago.

By contrast, insulation just loses heat. An R100 ceiling would just lose
24h(65-26.7)1ft^2/R100 = 9 Btu/ft^2.

Would you rather gain 29 or lose 9 Btu of heat per day in December?

Nick

wrote:
m Ransley wrote:


If it could automaticly close with a foam insulating plug when shaded
it could be a net gain.

That's better, but any skylight is a net gain if more solar energy enters
during a day than heat energy leaves during a day, which can happen with
several layers of glazing. For instance, 3 layers of R1 glazing with 90%
solar transmission would gain 0.9x0.9x0.9x460 = 335 Btu/ft^2 and lose
24h(65-26.7)1ft^2/R3 = 306, for a net gain of 29 Btu/ft^2 on an average
December day in Chicago.

By contrast, insulation just loses heat. An R100 ceiling would just lose
24h(65-26.7)1ft^2/R100 = 9 Btu/ft^2.

Would you rather gain 29 or lose 9 Btu of heat per day in December?

Nick

Might I point out that they call it a "greenhouse effect", after the
greenhouses, where glass panes contribute to the retention of solar
heat making the interior warmer than the exterior. Provided of course
they face south. Which in summer will make them heat up the interior
more than you want.

z wrote:

wrote:
m Ransley wrote:

If it could automaticly close with a foam insulating plug when shaded
it could be a net gain.

That's better, but any skylight is a net gain if more solar energy enters
during a day than heat energy leaves during a day, which can happen with
several layers of glazing. For instance, 3 layers of R1 glazing with 90%
solar transmission would gain 0.9x0.9x0.9x460 = 335 Btu/ft^2 and lose
24h(65-26.7)1ft^2/R3 = 306, for a net gain of 29 Btu/ft^2 on an average
December day in Chicago.

By contrast, insulation just loses heat. An R100 ceiling would just lose
24h(65-26.7)1ft^2/R100 = 9 Btu/ft^2.

Would you rather gain 29 or lose 9 Btu of heat per day in December?

Daylight is also nice...

Might I point out that they call it a "greenhouse effect", after the
greenhouses, where glass panes contribute to the retention of solar
heat making the interior warmer than the exterior.

Sure. Glass is a high pass filter, passing high frequency solar energy with
wavelengths shorter than 3 microns and blocking low frequency heat energy,
eg 10 micron heat from an 80 F black body.

Provided of course they face south.

That's better, with 740 vs 460 Btu/day of sun on an average December day
in Chicago. The calc above was for a horizontal surface. A south window can
provide more light than a skylight, esp if it's near a reflective ceiling
with a lightshelf below the window.

Which in summer will make them heat up the interior more than you want.

South walls get less sun than horizontal surfaces in summertime, and
shading them from higher summer sun is easy with overhangs.

Nick

I also have 10-15 year old velux skylights, motorized venting type.
They are absolutely freezing and one also is begining to leak. I can
tell you they are NOT good or even fair insulators at that age.
Perhaps the inert gas escapes in the first 10 years.
One inexpensive option is to go to Kmart, buy very heavy drape fabric,
and attach it (you can use tape on the upper end) to the inner screen.
This will provide at least some buffer between the room and the cold
skylight.
Another more attractive option is to buy cellular shades, cheaper over
the web, and install them against the glass, or preferably, just below
the glass. They offer / promise 6 R-value or so.
Another option I have not explored is whether the exterior glass hood
on those skylights can be replaced without changing out the portion
installed on the roof. By doing this you might be able to renew the
insulation value of the glass, which I am sure is lost by now.

But, one thing is clear- Velux is not that great of a skylight. My
wood is rotting from all the condensation, and the thermal value is
clearly lost, and I have a leak. With a similar leak on my Andersen
skylight, the rep gladly replaced the light under warranty, despite the
fact that it was 15 years old, and I was not the original buyer. Wow-
talk about standing behind a product. The issue was the seal of the
glass- "we had trouble with the seal on that skylight" he said. Wonder
if I have the same problemwith my Velux.








wrote:
z wrote:

wrote:
m Ransley wrote:

If it could automaticly close with a foam insulating plug when shaded
it could be a net gain.

That's better, but any skylight is a net gain if more solar energy enters
during a day than heat energy leaves during a day, which can happen with
several layers of glazing. For instance, 3 layers of R1 glazing with 90%
solar transmission would gain 0.9x0.9x0.9x460 = 335 Btu/ft^2 and lose
24h(65-26.7)1ft^2/R3 = 306, for a net gain of 29 Btu/ft^2 on an average
December day in Chicago.

By contrast, insulation just loses heat. An R100 ceiling would just lose
24h(65-26.7)1ft^2/R100 = 9 Btu/ft^2.

Would you rather gain 29 or lose 9 Btu of heat per day in December?

Daylight is also nice...

Might I point out that they call it a "greenhouse effect", after the
greenhouses, where glass panes contribute to the retention of solar
heat making the interior warmer than the exterior.

Sure. Glass is a high pass filter, passing high frequency solar energy with
wavelengths shorter than 3 microns and blocking low frequency heat energy,
eg 10 micron heat from an 80 F black body.

Provided of course they face south.

That's better, with 740 vs 460 Btu/day of sun on an average December day
in Chicago. The calc above was for a horizontal surface. A south window can
provide more light than a skylight, esp if it's near a reflective ceiling
with a lightshelf below the window.

Which in summer will make them heat up the interior more than you want.

South walls get less sun than horizontal surfaces in summertime, and
shading them from higher summer sun is easy with overhangs.

Nick

Nick no skylight I see offered has high SHG, this rating, a 50% lower R
value, cloudy days and heat loss make your statements of net gain
untrue. Now figure in extra heat load through summer, and you have a
major net energy looser.
But of course you do have independant results you can post to verify
your energy saving claims. Please post them.

"NeedleNose
Dec 28, 8:50 am

But, one thing is clear- Velux is not that great of a skylight. My
wood is rotting from all the condensation, and the thermal value is
clearly lost, and I have a leak. With a similar leak on my Andersen
skylight, the rep gladly replaced the light under warranty, despite the

fact that it was 15 years old, and I was not the original buyer. "

Did you contact Velux? What did they say? As for the rotting wood, it
would seem
to me that would be your fault. It takes a long time for condensation
and/or a leak to rot wood.
If the window lost it's seal you should have taken care of it a long
time ago.

m Ransley wrote:

Nick no skylight I see offered has high SHG, this rating, a 50% lower R
value, cloudy days and heat loss make your statements of net gain untrue.

I disagree. Where are your numbers?

Nick

Nick wake up and read other links mentioned, and post some facts, not
your usual unsubstantiated ramblings. You have proven nothing, you can`t
back up your claims, so you don`t.

NeedleNose wrote:

I also have 10-15 year old velux skylights, motorized venting type.
They are absolutely freezing and one also is begining to leak. I can
tell you they are NOT good or even fair insulators at that age.

Perhaps the gaskets are leaky.

One inexpensive option is to go to Kmart, buy very heavy drape fabric,
and attach it (you can use tape on the upper end) to the inner screen.
This will provide at least some buffer between the room and the cold
skylight.

Adding a few layers of plastic film underneath should work better.

Another more attractive option is to buy cellular shades, cheaper over
the web, and install them against the glass, or preferably, just below
the glass. They offer / promise 6 R-value or so.

IIRC, they only promise R5, including the window's R-Value :-)

Nick