Tips for Window Shopping?
StrawClayMark
| Posted in Energy, Heating & Insulation on
I am in the process of shopping for windows for the house we are currently building. It is a straw/clay, hipped gable, 1 storey house with four foot eaves. We live in Southern Alberta and so can have some extreme temperatures. What is everyone’s experience with the different window manufacturers and any comments on the common glazing options ie low-E, argon and krypton filled, as well as thoughts on PVC versus wood versus fiberglass? If you want to see more about our house, go to www.harvesthaven.com and check out “new buildings”.
Replies
I've not used the following window but I've heard a lot of good things about their product, mostly with regard to energy savings, not much with regard to install etc. Personally, if your into longevity go with fiberglass as it lasts a very long time. Second would be vinyl windows etc. Here's the site for the energy efficient window. They're new on the market and haven't established themselves as yet:
http://index.seriouswindows.com/residential.html
I've installed Milgard and they too have both fiberglass and vinyl lines of windows that are very good. Anderson is also of very high quality, they've been around decades and have top notch customer service.
To me southern AB means lots of wind and monster temp. variations in the spring and fall. Maybe that's not where you are.
I'd avoid wood frame windows, especially casements. In my opinion they can't deal with Canadian temperature and humidity ranges in the long run, even if you keep them up carefully.
j
We went with vinyl and vinyl/wood combo (VG fir wood on the inside). Low-E on all south facing windows. All are either casements or fixed.
No argon except in some large custom sealed units in a log truss.
The manufactuer was Westeck windows, a BC based manufacturer.
No complaints so far; house is five years old. Our temps range from -15C in Winter to well over +40C in Summer.
Scott.
PS...my advise would be to try to deal directly with a manufacturer if possible. See my thread on "Installing Custom Rake Windows" for a story on pricing.
Edited 10/9/2009 12:43 am by Scott
I might be off base on this, but here's my plebian thinking...
Even if you go hyper efficient in terms of windows, I think the most effective window is still only in the r-9 range for insulative value.
It can cost you hundreds of dollars per window to go from R-7 to R-9, and the window sellers are right there to encourage that additional expense.
But talk to the same window sellers about "black body radiation" and for the most part they don't have a clue what yer talking about.
Black body radiation is when an item, say a rock sitting in the middle of the field, despite being surrounded by 5 degree air, is in the middle of the night radiating it's stored heat into the abyss of space trying to heat it above absolute zero, so that it may actually cool below 5 degrees trying to do so.
Same for yer house.
A fella named kirchoff stated...."In fact, we can be much more precise: a body emits radiation at a given temperature and frequency exactly as well as it absorbs the same radiation.", in other words , as far as windows are concerned, either you let in in during the day, close the curtains, and keep it in, or it's goin out just as fast as it came in.
Two scenarios.... one with curtains, one without.
Sun shines through windows, heats up yer stone floor to 30C, night falls, yer stone floor radiates heat through the unblocked window just as fast as it came in during the day, only maybe faster, cause it's trying to heat up the absolute zero of outer space. And in winter, where you might have 8 hours of sun, 16 hours of dark, the equation of energy loss goes a tad to the negative.
whatever R or E you have ain't gonna change that rate of energy transfer a bit- the in is gonna equal the out. , But it costs a lot to ramp up from r-7 to r-8 or 9. and there ain't no real cost-effective benifet.
The scenario with curtains.... During day, high transparent windows (low r, high E) allow more heat in, warming stone floor more.
Come night fall close curtains, heat cannot escape as fast as the path to the absolute zero of outer space is blocked, ergo, the heat in the enclave is trapped, not being able to radiate as fast to outer space. It is slowed by the curtains, perhaps moreso if they are quilted.
Now when do you need all the solar heat you can get.....In winter of course.
And you want to let it in as much as you can, so why pay for windows that block the heat gain. rather pay for curtains that keep the heat gain constrained.
There is another alternative, perhaps better stated as an additional or augmentative opportunity, and it is likely greener,a and less costly than structural and finishing details..., and that is to erect a trellis, perhaps with a design element, about 3 or 4 feet away from the hyperinsulated straw bale house, and plant a fast growing vine such as hops, so that in summer, the house is actually shaded by the leaves, but come winter, the leaves drop, leaving the path free for the sun to shine in.
In southern AB, such a trellis might have a marginal additional effect in the winter by buffering high winds a tad and thus somewhat tempering heat scouring by winds from the structure in the winter.
just my plebian thoughts
if only for moral encouragement, you might wanna scope out
http://www.relocalize.net/greg_allen_interview_keep_the_green_alive
I met this guy way back when, he was inspiring, and he's designed homes so energy efficient that without a heating source, you had to open the windows to keep them cool.....and that was in the artic. Maybe my memory is deficient, but the Greg Allen is to my mind a Guru of Green.
Eric in Calgary
Eric
Wow. Thank you everyone for your thoughts. Some good thoughts that line up with some of my reasoning. I have thought about making window quilts of some sort for a long time for our current house which was built in the 70's and has a lot of glass. We do have deciduous trees that guard the two and half stories of glass we have on the south side from summer sun, that conveniently drop their leaves in the winter to allow more light and heat in. However, these windows were installed before low-e or anything else was invented. However, I met a Japanese fellow living in Vancouver a couple days ago who is just beginning to market a product developed in Japan that is like a low-e paint-on-able film that reduces heat loss 50%. Anyone interested, let me know and I will get some contact info out.Back to window quilts, I think I will revisit my old plans to use a special reflective foam insulation made here close to Lethbridge that unlike the R4 Air-Foil type of rolled aluminum/bubble pack insulation, rates out at R14 and is purchased by McDonald Douglas and other aerospace companies to line planes with. It's secret is a special thermal break membrane in the middle of two plies of bubble wrap and sprayed on aluminum (like they use in soft coat low e windows) rather than rolled aluminum. Just have to make this aesthetic and easily retractable.I will take a look at Greg's website.I still have to get a few details in place in order to calculate tuition for the Japanese timber framing workshop next year. Don't hold me to this as a quote because I have to see what some of my costs are going to come out to but it will likely be between $100-150 per day. The fellow teaching it, as you probably read, is one of a handful of surviving timber framers in the world that apprenticed as a temple framer and tea ceremony house framer, ... and just happens to be a personal friend. I appreciate your offer to spread the word Eric and to help out. We will likely be flying him directly into Lethbridge, so no Calgary airport pickup is needed, but we would really like to include you in our workshop. We will also be running one or possibly two straw/clay workshops next year as well.Anyone else out there interested in these workshops can check out http://www.harvesthaven.com and go to "new buildings" on the left hand column.I talked with a rep from Cossins windows in Calgary this morning who recommended HARD coated low-e, double pane for the entire house. He recommended hard coated in order to maximize solar gain and minimize loss. Normally they don't recommend hard coated as most people don't have four foot eaves like we have and thus need to worry about summer heat gain (hard coat supposedly lets more radation in and less out than soft e). We won't have the problem of too much radiation in the summer as the sun comes no where near the windows. He recommends metal clad wood frames though. I asked him about thermal bridging of the wooden frames. He said there was none. While he is mistaken on this, like it had been pointed out in this discussion by many, this is a very small heat loss compared to the window itself and poor insulation detail. Doing the insulation myself, I hope the details should be tight and right though. This is what I like about the straw/clay construction method; there is zero air infiltration as the wet straw/clay mix molds itself around the larson trusses and closes all cracks. It is like natural, breathable (no vapour barrier) spray foam in that respect. Back to Cossins windows, anybody have any experience with them? I haven't see the quote yet but they say they are comparable to Loen windows but with local factory prices.Also, anybody have any ideas on making a Trombe wall type of black wall in front of my thermal mass south walls to improve winter heat gain on the walls?
very god points you make, except this,
"Sun shines through windows, heats up yer stone floor to 30C, night falls, yer stone floor radiates heat through the unblocked window just as fast as it came in during the day, only maybe faster,"That spot of floor that was warmed will be radiating that stored heat energy out away from itself 360°, so only something like 5% of it will be flowing in the direction of the window.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
yer right, but also that the heat it radiates is also absorbed by other objects which also re-radiate, and some of that goes out the windows too.
Eric
If you run a heat load calculation on a house, you will find that plain old single pane windows with storms perform quite well compared to much higher cost double and triple pane assemblies.
Why? The dead air space.
The high tech windows with the low E coating are much better for reducing the cooling load on south and west exposures, but whatever you block during the summer you block during the winter.
It might be worth your while to visit http://www.hvac-calc.com and spend the $50 for a single use license and find out for yourself what the different types of windows do for heating and cooling loads... it just may save you a few thousand in unnecessary upgrades.
That 4 foot overhang and the resulting shade will do a lot to eliminate the need for low E options. The hvac-calc program offers a shading option (exterior and interior) for windows so you can see what happens. Not quite the same as doing it by hand the long way... but still illustrative.
If you want to reduce drafts, then provide a source of combustion air from outdoors to whatever equipment you are using to heat your home and water if that equipment burns something. Otherwise, the air needed to support combustion will come from the heated air inside your home, which is replaced with cold air from outside.
That cold air comes inside through poorly sealed windows (even high dollar ones installed poorly), any penetration on an exterior wall- such as spigots and electrical boxes, any attic ceiling penetration that isn't sealed like can lights and HVAC vents... etc.
A piece of equipment burning 100,000 btu of fuel for an hour needs about 1400 cubic feet of air to support combustion- not including dilution air. That 1400 cubic feet of air can come from indoors to be sent up the vent, replaced with cold outdoor air seeping in through every hole it finds in your home... or you provide mechanically forced combustion air if the equipment lacks provisions to do so.
Don't forget about the clothes dryer... not only may it burn fuel, but it also takes a lot of air from within the home and sends it outdoors.
Spending big dollars on windows and ignoring all of the other holes and infiltration details in a typical home is pointless... A controlled air leak like a barometric damper from outdoors to indoors is better than hundreds of uncontrolled air leaks.
Edited 10/9/2009 7:18 am ET by danski0224
Thanks Danski.We put in an 8" fresh air intake below the insulated slab to supply our planned contraflow wood fired heater and the gas boiler for in-slab heat and domestic hot water is located in a boiler house that will be shared by our house and new organic food store/alternative health center/organic bakery that is next door on our farm. I still have to look at what I can do with the dryer. It may be connected into a heat exchanger on the HVAC system. Any knowledge or ideas on the HVAC system is appreciated. I have gotten some really good guidance from my boiler guy, one of the few things I did sub-contract on this project, but always looking for diversity of info.
The 8" intake is a good step, but probably not big enough.
Easy to tie in an electric damper to close the intake when the boiler is off... might be able to do the same for that wood stove if that has some controls on it.
Was looking to install a manual damper for the 8" intake but electric may be an option too. Will have other make-up air in the air exchanger. Thanks.
where does your clothes dryer get its air?
Ed...I had to laugh and snicker when I read this.
once upon a time I thought that I could reduce my heating costs by scaenging heat from the dryer, but alas it took a couple of months before the condensation damage to to windows and the drywall underneath resolved.
I thought I was stupid and chaulked this up to stupidity, but yet in the maintenance work I've been involved withm I've seen folks who have ducted their dryers into the CA intakes of their furnaces for several years. Bathroom exhaust fans plugged solid with lint, Never took furnace apart to see what cruditations of wayward polyester fibres had welded themselves to the heat exhangers, But the huge quantities of moisture dumped by a dryer into a building is gonna condense in the insilation and cause it to sag, amplifying the condensation, reducing the effect of the insulation, and when the heat of the summer sun hits the walls with the damp insulation, gonna boil it off, along with the exterior paint. Absolutely totally antitheme to whatever the energy concious tenants hoped for...Save 40 or 50 bucks in heating costs and incurring several hundreds in re-painting costs
Dryer vents should be smooth and directly ducted outside. And cleaned annually.
None of that plastic expandable duct. One fire inspector told me it should be banned. It deteriorates quickly, perforates easily, and restricts air flow substantially.
But as to where does the air come from? In this era of hyper sealed homes, that is one freaking good question.
And HRV's- well they have to be serviced to maintain efficiency don't they?
Eric
Mark,
There's an interesting discussion of cold-climate windows at GreenBuildingAdvisor:
http://www.greenbuildingadvisor.com/blogs/dept/musings/passivhaus-windows
Martin Holladay, senior editor
http://www.greenbuildingadvisor.com
Thank you very much for the tip Martin.Mark
LowE coatings improve window performance in two ways. First they block radiant heat and second they improve the overall U-value of the glass system as well. Depending on what you really want from your windows - for example solar heat blocking versus solar heat gain - can make a difference in which coating might be best for your specific application.
Consider that 60% of heat gain or loss thru a window system is radiative, not conductive. LowE coatings work to block the passage of that radiant heat.
In ALL circumstances, a window with a LowE coating will improve energy performance over a window without a coating. The cost of a LowE upgrade (if it is an upgrade - I would suggest that most upper end windows include LowE as a standard anyway), will payback fairly quickly - particularly if you are in a harsh environment.
Field studies in cooling dominated climates, for example, have clearly demonstrated actual savings as high as 35% (possibly as high as 50% in some instances) in total year-round home energy usage when using a low solar gain LowE on the windows. Real numbers, not simulations. In heating dominated climates the improvements tend to be a bit more modest, typically in the 20%-30% range versus uncoated clear glass. Again, real numbers, not simulations.
There are two primary types of LowE coatings available - pyrolitic or hard coat - and sputter or soft coat.
Pyrolitic coatings are primarily fluorinated tin oxide and are applied to the upper surface of the glass in a process called Chemical Vapor Deposition or CVD. In the CVD process, vapor directed to the hot glass surface reacts to form a ceramic coating while the glass is still semi-molten in the tin bath portion of the float process.
Sputter coats are applied to the glass surface as multiple layers of metals and metal oxides in a series of plasma-filled vacuum chambers in a process called Magnetron Sputtering Vacuum Deposition or MSVD.
Coatings are often referred to as LowE, LowE2, LowE3...While LowE is used generically to indicate either a hardcoat or single-silver softcoat, LowE2 or LowE3 is used generically to indicate the number of layers of silver in the coating.
It is not uncommon for folks interpret LowE2 as two separate sputter coatings applied to surfaces 2 and 3 of a dual pane IG unit, but that is actually not the case. Coating both surfaces 2 and 3 in any IGU configuration is almost a guarantee of broken glass or seal failure because of heat trapped in the airspace between the two lites. Dual pane windows (with some very rare exceptions) do not have LowE coatings on both lites.
In fact, when dealing with triple pane IGU’s and having LowE coatings applied to two different lites the coatings are almost always applied to surfaces 2 and 5 in order to avoid excessive heat buildup in the IG airspace - if for example the coating was placed anywhere on the inner lite rather than the two outboards.
Dual or triple silver sputter coats (low solar heat gain products) are generally built to surface #2 of a dual pane IG unit, while a single silver (high solar heat gain) or a pyrolitic coating is often built to surface #3.
In a heating dominated climate, the two reasons for placing the LowE coating on the #3 surface of the IGU is to allow for solar heat gain in the winter and to block the transference of the heat from inside the home to the outside.
High Solar Heat Gain (or HSHG) coatings and Low Solar Heat Gain (or LSHG) coatings are all designed to block far - or longwave - infrared energy. This is the range that includes typical household-produced heat. This is also the wavelength of heat that is produced when the sun warms an object – the heat you feel "reflected" from a hot wall or sidewalk on a hot, sunny summer day (absorption to reradiation). While direct solar energy is shortwave IR, the heat released by a sun-warmed object is longwave IR…and hopefully I that makes sense as I wrote it.
Anyway, a typical hardcoat or single-silver layer softcoat works in this application since all types of LowE coatings are designed to block far infrared energy - thus keeping winter heat indoors or summer heat outdoors - but no high solar heat gain coating is designed to be effective at blocking shortwave infrared - thus allowing direct solar heat into the home - winter or summer.
Placing a high solar gain coating on surface #3 maximizes the level of solar heat gain thru the IG unit and effectively retains that heat indoors which can be an advantage in winter and can also be a disadvantage in summer if the home wasn’t designed to block the direct solar gain by use of shading whether trees or roof overhang. But in a heating dominated climate and in a well designed home, the potential advantages of direct solar heat gain during winter months (again depending on climate and design) are obvious.
A Low Solar Heat Gain product, on the other hand, is designed to block both near and far infrared energy. It will help prevent thermal energy - including direct solar gain – from passing thru the window in both summer and winter.
Low solar heat gain coatings are usually placed on glass surface 2 to maximize effectiveness against direct solar gain by blocking solar heat before it can pass into the airspace in the IG unit – and into the home.
Argon gas between the lites of an IGU results in an increase in unit performance of 16% at 100% fill rate. Drop the fill rate to 75% argon and 25% something else (typically nitrogen) and the unit energy performance is 12% better than when using an straight air fill. At 50% argon fill the performance is 8% better (notice the pattern?). Energy performance improvement is linear from the 16% at 100% down to whatever fill level the manufacturer desires.
Edited 10/14/2009 2:06 pm ET by Oberon
Hi Oberon.Thank you for the superb response. It helps clarify a lot of the conflicting information I have received. Due to the 4 foot overhangs on all windows except my south aspect "Sun Bump" and on the western bathroom projection, I am not worried about summer heat gain but I am very interested in maximizing winter heat gain. On that note, it sounds like an HSHG, or hard coat low-E is right for me, at least on those south windows, and particularly on the sun bump. However, one remaining question I have is whether triple glazing blocks too much of the incoming heat on the sun bump? Should I be double glazing that with a hard coat low E?Then the next quandry is the extra expense of triple glazing worth it for the north and perhaps western windows? And if so, with what kind of low E on them, hard or soft, single, double or triple coat? We have dramatic temperature extremes here. Overall, we have one of the mildest winters anywhere in Canada outside of the west coast of BC, but we have extremes. It can get as cold as -37 degrees C in the winter when the north winds blow. However, when the warm west Chinook winds blow, it can be 10 degree C above freezing in January or February. I have full sun to the south, shade to the east, of course no direct sun and partial shade on the north but with a good north wind break, and partial shade on the west. Have any thoughts on how to combine these options in a cost effective strategy(so that my investment actually has a chance at coming back to me in a reasonable period)?I have included a floorplan if you want to take a look.Thanks again!Mark
Hi Mark,
You can maximize solar heat gain by using either a hardcoat or single silver softcoat LowE coating on the windows that you want maximum solar gain thru.
Really it depends primarily on what the window manufacturer chooses to use in their product. Both versions will provide you with similar performance numbers.
A quick rule of thumb when thinking about glass options in windows is:
one lite = R1
two lites, either dual pane or single pane with storm = R2
three lites or two lite with a LowE coating = R3
add argon to a dual pane with LowE = R3.5
three lites with one pane coated = R4
three lites with two panes coated = R5
triple pane with two panes coated and argon = R6
triple pane with two panes coated and krypton = R6.5
Okay - again a very general rule of thumb. Other factors susch as frame material, air space width, spacer, type of LowE coating will affect those numbers; and R value is not the best method of assessing window performance anyway - U value is better.
In your environment, triple panes will provide improved energy performance over dual panes. Using US U value, the very best dual pane perfromance numbers available (that I know of) is U.24 - which is actually better than some triples.
But even good, but not the best, triples can get you down in the U.19 range or so. The best triple performance is going to be in the U.13 or U.14 range.
Is the improved performance worth the extra money? Eventually you will reach a point of diminishing return, where additional performance will not offset additional cost...which is kind of the point of the entire thread.
I live in Northern Wisconsin. It gets cold here as well, and I put triples in my daughter's new house (with moderate gain LowE on two lites and argon fill - U.17 for her widnows). If I were building new, I would not hesitate to put triples in my house.
If you are going to the trouble of super insulating, then I would suggest that not putting in the very best performing windows that you can afford is partially wasting your whole house insulation efforts.
This doesn't mean that they have to be triples, just that you want the best numbers that you can afford - and keep in mind that the very best window in the world if poorly installed ends up being a waste of your money.
Thank you again for the informative answer. Roger on the installation. I plan on doing that myself. I am just crunching through quotes right now to find that tipping point of economic comfort and probable returns. I am also still considering making some sort of architecturally fashionable window quilts with this super reflective insulation manufactured in our area. Our contra-flow heater and shared high efficiency gas boiler/in floor radiant heat system will also lower the heating costs in that tipping point equation.
You are welcome and good luck with the project. It sounds like you have it working well.
If I was window shopping, I'd wear my best Easter Hat.