Low-E glass?

[djmcmath]

I'm getting ready to put a handful of new windows into the old house -- replacing 80 year old windows -- and there's some discussion about low-e glass (or, technically, I guess, low-e glass _coating_). Specifically, there are two windows with south-facing exposure, and two with north-facing exposure, and I'm thinking it will be prudent to put in the low-e glass for the southern pair.

My thoughts:
1 - Reduce heat load on a south-facing room, thus reducing A/C load and hopefully reducing the delta between upstairs and downstairs temps. I think it will still be bad, but I'm hoping that good windows will help.
2 - Ignore the fact that less heat will be let in during the cold months; the room is upstairs, and heat rises.

My wife's thoughts:
1 - Cosmetic -- is there a discernible difference between low-e and normal glass? Will people look at the south room and say "What's wrong with the glass in there?"
2 - Warmth -- she always liked to play in the warm sunny spot from the window when she was a kid, and is concerned that we'll be producing a cold and lifeless child's bedroom. Does the low-e glass still let in some warmth, or is it really that efficient?

Thoughts from the board? Anyone have a wife with strong opinions on the cosmetic effects of window glazings? Head load impact -- will it make any difference, or is this just a wasted battleground?

Thanks in advance,
Dan

[red-beard]

Put the low-e in all places. I can't tell the difference from the inside.

[stomachmonkey]

I've got an E facing wall in my family room. Ceiling is open to the second floor. Have two rows of 3 windows each about the size of a standard door.

It's a lot of glass. Low E. The sun that comes thru it destroyed a brand new leather couch set in less than 2 years.

This winter we had some cold days but the sun here in TX is strong. All the heat was rising and flowing into the second floor making the AC kick on when it was 30 outside.

I put in solar screens, $450 for all six installed on the outside. This type of material. Made a HUGE difference in the UV coming thru.



Room is a bit too dark for my taste.

In retrospect I should have opted for them to be built as roll ups on the inside. Wife objected since the upper 3 would have to have been motorized with a remote.

[Tobra]

You could still do roll the inside roll up thing. You thought about a ceiling fan in the mezzanine level?

There are UV coatings that appear clear rather than tinted.

[RWebb]

I put low-e all around (required for my energy savings tax & other subsidies). For sun exposure areas I also used PPG tinted glass with a low SGF - solar gain factor.

Arch.s on the bbs can tell you more info - not sure what abbreviations are in vogue right now.

Shading the outside will always work better, esp. for the direct solar beam (which is 90% of the total short wave radiation). Diffuse reflections will account for ~ 10%. Long wave inputs will be diffuse in nature but will not penetrate glass very much (from either direction). Low-e - the e= emissivity and that will make the house a bit warmer in winter.

[Zeke]

I've been installing windows and doors with LowE for 20 years. It works. You can have it in the window so the heat stays inside or the heat stays outside or both. Actually, it works on infrared rays going in each direction, but the effect can be maximised by which internal glass surface the coating is placed.

Then, you can upgrade to LowE on both internal surfaces. Some companies call that LowE "squared," or LowE 2. LowE also reflects UV rays pretty well, but there's no heat gain or loss with UV.

Here's what the sales people don't tell you: and window is only a small part of the total energy envelope. Most houses have around 10% of the floor area for window area allocation. If you add in outside facing walls and ceilings to attics, your total fenestration could be as little as 5% or even less.

You can't ask something that is 5% of the envelope to produce dramatic energy savings. It will help, of course, because you will be reducing convection through the windows to almost zero. But heat gain on a 2 x 4 studded wall with little or no insulation facing the sun will heat up a room faster than Sarah Palin walking into a democratic caucus.

And know this fact: the best window you can buy is about an R5 with most being around an R3. That's why they don't rate window performance on the R scale. They have there own "emittancy" scale. Go for a product that is close to 40 on that scale.

And do the rest of the stuff on the energy savings list like fully weatherstripping all entry doors and back-damping any vents to the outside. Fully insulated attics have been shown to be the best investment. You should have about an R40 up there.

[Tobra]

Oh, and for your attic, that heat reflecting stuff you put on the inside of the roof works pretty well.

[djmcmath]

Thanks for all the informative replies!

For background: the house is a "bungalow," which is basically like a "cape cod," except with one fewer dormer, as I understand house styles. Or in other words, the space in question has, for walls, two gables and the roof. For insulation: I laid down a layer of the shiny reflective stuff, which didn't seem to help at all. But it was cheap, and really easy to install. Then I put in 2" extruded polystyrene foam. Then I put in a layer of R-19. I would have put in more, but I only had so much depth of roof joist to play with, and R-19 was really deeper than fit.

My take on this, then, is that (a) given the poor insulation in the rest of the space and the enormous heat load from the roof, it won't make much of a difference and (b) you really can't tell by looking at it anyway. Or in other words: make the wife happy and skip the low-e glass because it won't make much of a difference anyway.

Sound about right?

Thanks,
Dan

[Zeke]

No, don't skip it. It's cheap and standard in dual pane windows. You can skip the argon gas and other add ons.

If you order grids for the windows, you may see a slight greenish tint on the white grid from the outside if the LowE is placed on the inside of the outside pane (typical). It does not interfere with light transmission.

Your wife must be rather particular. Maybe she wants the neighbors to see the true color of her curtains.

Tell her I said to relax and worry about something a little more important. Tell her LowE prevents skin cancer (no proof of this, but it's possible).

[djmcmath]

Originally Posted by milt

Your wife must be rather particular. Maybe she wants the neighbors to see the true color of her curtains.

Yes, yes she is. I can never be sure why she's being particular about certain things, but ... seeing the true color of the curtains is as good of a guess as any.

Tell her I said to relax and worry about something a little more important. Tell her LowE prevents skin cancer (no proof of this, but it's possible).

I love it. I'm totally doing that. She'd buy it, in spades. Milt, you're a genius and a hero.

Dan

[Scott Douglas]

We found out just how much the sun really added to warming up our house in the winter. It was a lot. We're now adding central heating.
As for the warm sunny spot to play in...I wouldn't count on it being there if you go LowE. My wife used to sit with her back against the slider in the family room to warm up on cool mornings. It is east facing so would get the morning sun. Not any more as the slider is LowE too. Our house never did have great heating (three wall furnaces, one of which we've never used in 26 yrs of living here) but without the sun now doing its thing thru the windows we are finding out just how bad it really is/was.

[Zeke]

Scott, I have personally experienced the lack of infrared radiation on sliding doors while installing. Open one up on a sunny day and stand directly in the sun and then stand behind the open panel that is parked in front of the fixed panel. That's where it's doubled up giving 2wice the effect.

That alone will sell a door to any skeptics.

Not only that, but new windows keep dust, pollen and noise out due to the excellent weatherstripping engineered into all new certified windows. It's not the glass so much that kills noise. Sit in your car with the windows up and then crack them just a bit. Listen to the difference. Then realize that cars don't have dual panes.

It's all in the weatherstripping.

Window sales people hate me because I can provide the performance w/o the upgrades which are all profit. Sound familiar?

[stomachmonkey]

Originally Posted by Tobra

You could still do roll the inside roll up thing. You thought about a ceiling fan in the mezzanine level?

There are UV coatings that appear clear rather than tinted.

Got the ceiling fan. Room is 25x25ish with a 30 ft ceiling.

Pic from when house was under construction, those are the six I'm talking about.

The guy in red is a good 5 feet closer to the camera.

Originally Posted by Tobra

Oh, and for your attic, that heat reflecting stuff you put on the inside of the roof works pretty well.

Got that thank god. Definitely keeps the attic from feeling like the depths of hell.

[RWebb]

Dan - call you utility and ask them if they will give you a free energy audit - those are common in Oregon.

you do want low-e glass.

you may want to increase ventilation in the attic - best if you can shut that down for winter

do you have vents in the "ceilings" of the roof that runs all the way around the house outside the walls?

also state if you know many of the terms for house construction...

[djmcmath]

RWebb -- utility audit would likely be somewhat humorous in this house. It was built in 1927, lit on fire during the Great Depression, then apparently repaired by a three-armed homunculus. I'm slowly working my way through the process of modernizing this thing, but I suspect that an energy audit would tell me that I'm losing heat through everything that I haven't touched yet. But thanks for the idea.

Shutting down the attic in the winter isn't going to be practical; that'll be the kids bedrooms, so they'll have to be inhabitable all year round.

I opted against the vents in the ceilings. They're good in the summer, in that they move some fresh air up through the ridgeline, which helps to keep roof temps down and can prolong the life of the roofing. However, in winter, that's a layer of fresh moving air instead of a layer of insulation. So I opted for 2" of EPS foam instead of 2" of roof venting.


StomachMonkey -- I'm curious what heat reflecting stuff you put in your roof that worked so well. The stuff I put in didn't seem to have any effect. I didn't exactly do the science experiment, but I certainly couldn't tell the difference until I started putting the foam and fiberglass in.

[RWebb]

it's perfect for an energy audit - they want to find the houses that will save them the most

[M.D. Holloway]

Check out Guardian Glass' Diamond Guard and Sun Guard - provides the thermal insulation of double pane glas in one sheet. Its also stratch resistant.

http://www.guardian.com/guardianglass/glassproducts/SunGuardAdvancedArchitecturalGlass/index.htm

DiamondGuard Scratch Resistant Glass - Guardian

[stomachmonkey]

Originally Posted by djmcmath

StomachMonkey -- I'm curious what heat reflecting stuff you put in your roof that worked so well. The stuff I put in didn't seem to have any effect. I didn't exactly do the science experiment, but I certainly couldn't tell the difference until I started putting the foam and fiberglass in.

Radiant Barrier. Not sure of the exact brand/manufacturer. I can check over the weekend.

[john70t]

I'll second the energy audit, especially a free one, and suggest you pick the brain of every person doing it. Write it all down for later consideration. The energy savings a decade from now will be worth it, if not the comfort level.

This past summer, I got one for $300($100 DTE rebate) and they did a very thorough job, IMO. Well worth it.
-Attached a front door fan which sucked all the air out of the building, and found numerous air leaks around doors and areas I thought were sealed.
-Went though the house with an infrared camera which identified where the insulation was working, and where it wasn't.
-Gave me a video recording and complete write-up of the previous, followed up and later helped with the rebate forms, and recommended possible fixes.

I suggest the energy audit first because it's no use spending $10,000 on windows when the wall insualtion could be bad, a ventilation system needs improving, or another factor is affecting the home.
Even a hundred dollars of caulk might make more of an improvement.


On the drafty doors, we simply added curtains. They stop the draft in the winter, and the sunlight in the summer.

[911pcars]

Originally Posted by stomachmonkey

Radiant Barrier. Not sure of the exact brand/manufacturer. I can check over the weekend.

Careful. Some of the claims of radiant heat barriers (thin foam/aluminum foil sandwich) are quite optimistic. Some claim insulation qualities equivalent to fiberglass bats.

I would heed Milt's suggestions re: existing home insulation versus significant energy savings from lowE glass.

Sherwood