Top performer, higher price:
High-performance windows, such as this triple-glazed unit made by Thermotech Fiberglass, have low U-factors. Are they worth the higher cost?Image Credit: Thermotech Fiberglass
More Q&A Spotlight
Randy George is in the final planning stages for a new house he will be building this summer in Vermont, and from the sound of it he won’t have much trouble staying warm through those long winters.
In addition to R-45 walls, an R-65 roof and R-20 slab, the house will have air infiltration rates lower than one air change per hour at 50 pascals of depressurization. Although not quite meeting the Passivhaus standard, that’s extremely tight construction.
George wants his windows to have a U-factor of no more than 0.2 (equal to R-5), but his contractor tells him he doubts that windows meeting that criterion will be worth the expense. “All along I’ve felt that one of the high-performance Canadian windows would be critical to the performance of our house,” George writes in his Q&A post at GreenBuildingAdvisor.
But after meeting with the contractor, George went back to the heat-load calculator he’d been using for another look. While his original calculations showed that he’d need a heating system capable of producing 20,000 Btuh, reducing the R-value of his windows from 5 to 3 would only boost that to 22,500 Btuh. Projected heating costs would go up only $150 a year. Even after juggling the numbers slightly — boosting the required Btu and adjusting the cost of propane upwards — the difference in heating costs would be about $200 a year.
“I’m assuming that the cost difference between these windows would be several thousand,” George writes. “This is making me question the wisdom of the good windows. Can anyone tell me what I’m missing in all of this, or is there a little too much hype surrounding the ‘good’ windows?”
Payback is a more complex than it looks
GBA senior editor Martin Holladay doesn’t find much to challenge in George’s number-crunching,…
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24 Comments
Attachments
That's a conversation I really look forward to as I've long felt it offers some useful applications most especially in mixed climates. In our case, we could use the attachment in summer. Or maybe I'm just dreaming. I look forward to the test results and product listings.
Thanks Peter, and Scott.
Share the numbers
Please provide heating degree days for the proposed site along with the glazing area and current energy option costs. This will help viewers follow the cost/payback discussion.
not worth the cost
Is a subjective and potentially incorrect statement. Given the right SHGC and u-value it may be entirely possible to lose inches of insulation around the envelope. Many of the passivhaus projects in colder regions of Austria alps are able to get away with sub-R60 assemblies. In part this is due to glazing with SHGC north of 0.55 and U-values south of 0.13 [I-P]
re
I cannot help to constantly think the opposite question. Are triple pane windows good enough?
In my house, the 200 square feet of ~R3 windows lose more heat [~4600btu] at design[70Delta] than my entire roof [3850 btu, 1650 sq ft, ~R30]
Adding a double pane storm to those windows will save more btus than adding another R20 to the roof.
Maybe a better question is "How do you get the U value you need to have, for the money you have to spend?" I know for instance that I have had quoted[normal lo e] 8 foot sliders at 5-8k, where there is perhaps 2.5k of 'glass value' there.
[self important rant]
I like to think I can occasionally add to the conversation. When one offends more than one aids, it is not one of those times. That section of quotes seems.....irrelevant
[/self important rant]
Consider your heating and cooling distribution system
Another thing to be considered is the elimination of convective loops when you use high performance windows. This will considerably simplify your duct system or radiant heating system, as you will no longer need registers or radiators at every window to counteract those loops. Piping and duct runs will be shorter and you will be buying fewer radiators or registers. This may easily make up the difference in window costs.
Triple-Pane Windows Fight Frost!
Another very important consideration in deciding whether to split for the triple panes is the potential for frost on the inside of windows. At elevation, on cold nights, we see frost build-up on double-pane windows. Although the installation of triple pane windows does not eliminate the chance for frost build-up entirely, it greatly reduces the chances that it will occur, and allows homeowners to maintain higher interior relative humidity.
As we all know, the frost will melt and drip, which can stain the window sill and even cause mold!
When you factor in the potential maintenance costs for double-pane windows, I believe the triple pane windows will make sense.
http://greenlinearchitects.blogspot.com/2011/01/frost-on-windows.html
triple pane costs 30% more
I've gone through this scenario recently with my builder and declined the 30% up charge for triple pane. Whne considering the fuel costs of burning wood, its hard to justify thousands of dollars. The other factors are somewhat subjective to each individual- humidty levels, comfort etc.
comfort and simplicity
First of all...triple pane windows also need insulated frames. Once that is said I'd like to second David Peabody's earlier comment - the high performing window eliminates the need for a heat source under the window which can save you thousands of dollars.
I like to use fewer but larger windows. A window twice as big doesn't cost twice as much. Using stationary windows where possible will also lower the cost. And, remember that casement and awning windows are much tighter than double hung windows.
Window Attachments
I do a lot of research and one particular window attattachment has really stood out. It is called In'Flector. Windows have or eventually will have four deficiencies which a high performance window attachment can solve. This is a multi-film material I've seen in a panel, roller shade, and vertical blind form. It insulates, air seals, reduces solar heat gain in summer, and increases or adds heat or mitigates heat loss in winter. This space age product is also being tested by LBNL and NFRC. The product is currently being used in military installations and other government, commercial, and residential buildings where computer models have shown it can perform and have a significant payback.
Treble glazing?
May I mention that I have fitted quadruple glazing in all my bedrooms.
That's two sets of double glazed e-glass per window.
As an experiment one bedroom on test went through this winter without any heating, other than that through an open door into our rear hall, the hall is maintained at 22C.
With an air temperature outside of minus 9C and a ground temperature of minus 28C that bedroom maintained a temperatures between 15.4 and 19C.
For most of the winter that bedroom was around 19 to 21C.
I just like to be able to stand/sit in front of a window and be comfortable.
High Performance Windows worth Cost
I would suggest that this conversation is pedantic and just a little myopic. The loss or gain of a single, double, triple or quadruple pane is dependent on a whole lot of factors. There is solar orientation, seasonal shading or lack thereof, thermal mass, solar gain, tightness of structure, etc., etc,. There is great and intelligent discourses about the "tightness of a home or structure" and the insulative values of various products be they translucent or otherwise endowed. The simple reality proven out thousands of years ago is that the amount of thermal mass or ability to retain heat /cool temperatures over extended - even protracted periods of time proved to be the the most effective means for the the comfort of its inhabitants. I would humbly suggest that the utilization of electronic or mechanical controls to control the immediate environment of human habitation serves only serves to exacerbate the disconnection of humans from the environment around them and ensures the indifference to any and all environmental concerns relevant to our species immediate or long term survival.
If you can clearly define or offer me one single example of a species upon our planet (present or past) that has successfully created an environment that is entirely separate from its environment then I will humbly acquiesce to your discourses. If you cannot I will continue to contend that isolation of the present set of assumptions pertaining to the human environment in terms of building, infrastructure, be it residential, commercial or industrial flies in the face of the survival of our species.
The thermal wheel SIMPLY = the thermal wheel!--- that is a proven terrestrially axiom at least in context to this rather minor planet in the universe.
However, I will suggest at least at this date in time - not having received your response that nature and history can provide some very valid answer. Yes insulation is a factor, protection from decay is another,: however it has been not isolation (re:insulation) nor has it been exclusion from the immediate environment that has provided the continual survival of many a species of plant and animal through millennium or more it has been adaptation. And by your own culturally accepted dictionary the Merriam-Williams ; is defined as 1) -a - the act or process of adapting, 2) -a- the adjustment of a sense organ to the intensity or quality of stimulation. b- modification of an organism or its parts that make it more fit for existence under the conditions of its environment.
Note: Adaptation is not exclusion,denial, omission, or human science! It is evolution,not retention.
Simply put it is; not the knowledge of the box, it is simply the desire, drive, commitment and drive to think outside of the box, yet with the respect of the world or environment the box has and does exist in.
With great regard,
Rhaud.
ps. I prefer to move the coffee table and consider a different route.
My apologies
My diatribe was ill conceived and unwarranted. Can you not conceive of the reality that the limited, yes LIMITED resources of this present day world of buy and sell and business as usual cannot sustain ourselves (humans) or the planet whose only purpose is to sustain life, even our human ones, even though it appears as though everyday we try to ensure our own demise.
THETHERMALWHEELISATHEWHEELGRABHOLDANDSURVIVE!!!!!!
bring it back to earth
I've spent the past few years building passive solar houses and hope to go for a more "super insulated" approach on the next one but I still can not make the practical case for triple pane windows. First of all, the cost increase from a Hurd H3 wood/almuminum clad double pane to a Termotech triple pane is likely to be in the range of $6000 for a 1800 s.f. house. Most of my glazing is on the south side and all of this glazing would suffer from lower SHGC. Cardinal 179 glass on the #3 surface would bring in 70% of the heat. The best triple glazing might be around 60%. I can see the advantages to having a lower peak heat load and greater ease in heating from a point source but from a total energy consumption versus cost standpoint I think that the triple pane windows are last on the list. I'll go with R40 walls, R60 roof, 1 ach 50, and skip the high end canadian windows. If my glazing was not facing south or I had sound control issues I might reconsider. I'm as idealistic as the next guy but we have to bring these things back to earth and what can be done for the least cost. For south facing windows in Asheville nc, triple pane windows make no sense.
Expensive windows
Samuel,
I'm with you, in your location, triple glazed windows would yield a very slow payback. I have looked at replacement costs for 4 north facing windows on our house in Minneapolis. They are large double hung, thermo pane with a storm. The cost to replace these 4 windows will pay our entire heating bill for the next 10 years, it does not make economic sense, to me at least.
I am all for super low energy housing and if you can build in the price of very efficient windows, do so. From a window replacement standpoint, one should crunch some numbers.
Window shades worth looking into
I had ruled out the high cost of replacing windows with triple glazed so ended up installing Hunter Douglas Duette Architella honeycomb semi-opaque shades in our great room windows. The r value is supposed to be around 3 and they are the only shade I found that qualifies for the tax credit. I was so impressed I got more for all 3 bedrooms the next year . On a 25 F day the temperature next to the double glazed window was 22 degrees colder than the room side of the shade. Their use in summertime makes a huge difference in solar heat gain. Because they are opaque, they don't darken the room significantly which is a big plus. I hate curtains and like the clean look of cellular shades anyway, so I was thrilled to find a great looking shade that performs so well. I am all for triple glazed windows and wish we could have afforded them when the house was built, but the shades are definitely making a huge difference in the comfort of our home. I am hoping someday triple glazed becomes the norm and maybe the price difference won't be so great.
It seems to me that in Quebec that triple glazing is fast becoming the norm. Apart from the more reasonable prices it is now quite possible to find discarded double glazed windows to double up on double glazed windows that are still in good shape. I wouldn't recommend it unless the recuperated window is high end or small. Big thermopanes that are hard to install have a tendency to fog up.
economics
one key points is where do you want your money to go, when payback is even
do you want to send it to the utility company (more than likely to drill, mine, and burn)
or send it to the window manufacturer
i like the idea of sending it to the window manufacturer, and in the end, you have free windows when the energy equivalent is paid off
i will admit myself though that i'm having a hard time with using most triple panes on the south end; the high end ones that work better as far as SHG cost two arms and a leg
supply and demand
My guess is that someone building this type of house is doing so not solely out of financial motivations, even though those are often quite compelling and sufficient. Another consideration might be that by purchasing triple pane windows, one is creating demand for the product. That will motivate vendors to increase supply and that will bring costs down. Ultimately, that will encourage more people to purchase those windows including those who’s only concern is their bottom line. We all benefit if triple pane becomes the norm for cold climates. I for one am grateful to the early adaptors of dual pane over single pane. They helped drive down the cost for the rest of us and now single pane windows are energy hogs of the past.
Windows
Cripple Creek Construction; We only build hand hewn log homes. PROPERLY done, these are the most energy efficient homes built. We use Kolbe & Kolbe double pane, low e-glass windows and to further their ability to prevent heat loss, we usually build raised panel shutters from re-cycled lumber. Past experience, 25 years, shows us that using wood shutters reduces heat loss by about 20% on customer heating costs. I do not have scientific evaluations, only satisfied clients.
Four panes of glass eh? I
Four panes of glass eh? I can see the snake oil marketing campaign for 6 panes already… just a matter of time. NA engineering at its finest, I guess tripples weren’t bringing in the kind of sales the industry was expecting…onto polishing that turd some more.
It all boils down to what we as builders/home owners consider "high performance”.
I wouldn’t qualify tripples (even quadruples) as HIGH performance… Performance at best, but at the end of the day it’s still not enough for HP homes.
Heat mirror films, PV window films are just a couple of the "features" we should be expecting in HIGH performance windows and demanding the industry to make these standard options…..
The industry is riding on market’s lowered expectations when it comes to glass, and until building codes, standards and building methods demand it…why improve it, they money is good the way things are..
No failure discussion?
In nearly every triple glazed / heat mirror discussion I come across there's at least some time spent on the increased failure rates over double glazed units due to increased weight to frame strength, more seals that can fail; there's also the well known problems with the reliability of some triple glazed products/manufactures in the past. But so far in this thread the issue has not appeared?
Heck, I had a representative from Big Window Co in the other day (that doesn't carry triple) who claimed triples will _always_ fail given time. Well, I have little idea if there's basis for that statement, and I don't know about the long term reliability of the current crop of triple products. I do however feel it is reasonable to assume triple reliability is likely at least somewhat less than that of a standard double glazed unit, perhaps substantially less. Adding the reliability finger on a scale already showing marginal benefit versus cost seems to clearly tilt in favor of double glazed.
RE: No Failure Discussion
Mark
Very interesting point. When I inquired with a local Window Mfg about their triple pane windows, they strongly discouraged them citing high cost/long payback period and problems because of the extra weight. They said they only sell the triple if the customer insists. They only sell their windows locally installed by their people and guarantee the windows for life. Now I'm thinking their reluctance is due to high call back rate due to failures.
failures, heat glazing, cost vs payback
Manufacturers dont offer less of a warranty for their triple pane products so I doubt failure should be included in the debate although if anyone has good figures we would all love to know..
Since heat glazing has been brought up I will offer the most commonly listed drawbacks; low VT, lower SHGC, questionable long term performance.
Comment #13 applies to me being an Asheville home builder, Hi Sam! Sam builds amazing homes by the way. Aside from the excellent reasons already given to upgrade to triple, design can drastically reduce the cost and complicate the payback argument even more. Windows that are bigger but fewer, more fixed (less operable), but most importantly focusing on orientation whenever possible increasing windows on the South and fewer, smaller windows on the N, E and W. This can make the cost to upgrade to triple everywhere except the South very affordable.
We recently completed two of our passive solar, Springtime Cottage plans in Asheville NC and upgraded to triple pane everywhere except the South. The cost to do so: around 300$. We didnt try to model the payback, it was seen as an affordable upgrade that brings good marketing and better comfort to the homeowner.
I will agree that trying to find affordable triples for the South is scary and difficult. Its important though that we all actively pursue the price to do so. Even just getting the costs from the reps will help prove demand and hopefully reduce costs for everyone which seems to be happening.
I must add payback doesn't account for rising energy costs very well and doesn't account for the Hidden Costs of our dirty energy at all. Better comfort, less potential for frost/condensation, less sound transmission, simplification of some mechanical systems are also tough to account for.
I included a rendering of the cottage I mentioned mostly for shameless promotion but it does visually show how massing South windows that are not necessarily triple paned can cloud the debate for triples in more mild climates like Asheville. HDDs:4308
Triple Pane Windows
I don't understand why one is concerned about expense, energy savings and payback with triple pane windows for a 500 sqft curtain wall? As Marge Shott (owner of several car dealerships and one time owner of the Cincinnati Reds once said "if a car's MPG is a concern, you probably can't afford the car"!
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