Windows are like big holes in your insulation
From a strict energy efficiency view, windows are a really bad idea. If you want the most energy efficient building, make it one with good insulation and no windows!
When designing and building an energy efficient structure, we spend a great deal of effort creating a thermally resistant building shell that can effectively control heat loss. Placing windows in our carefully designed insulating shell is essentially cutting big holes in our work. Even the best windows available have insulating properties that are only a small fraction of the performance of an average wall system. Add to the mix the fact that windows provide a path of air leakage during all seasons and the potential for unwanted solar heat gain during the cooling season.
Of course, windows are vital for a healthy, safe building and no one would seriously consider doing away with them. We’re stuck with windows, thankfully, but they can be energy wasters.
So, you may ask, if windows are such energy wasters, shouldn’t we put the absolute best performing windows into our homes in order to minimize those loses?
If you are constructing a new home, the simple answer to that question is yes, you should buy the best performing window system appropriate for your climate that your budget can bear. You will save money each and every day of the life of that building.
And since windows are being installed anyway, the cost differential between an average and a high performance window is relatively minor. The simple payback on your additional investment will likely be a reasonable period, depending on your climate.
Changing Windows Is Expensive
When it comes to remodeling and upgrading a home, the question, “should I replace my windows” is not nearly as easily answered. Retrofitting an existing home with new windows is an expensive proposition. There can be significant labor expense in exterior trim and possibly siding removal and repair or replacement, as well as interior drywall or plaster and finish carpentry work.
If you own a home built before 1978, there will be additional expense associated with testing for lead based paint on and around the windows being removed. If lead is found on surfaces that must be disturbed in the job, special measures to contain and clean up the lead dust must be implemented as a part of the EPA Lead Safe Renovation, Repair, and Painting Rule (RRP).
Unless you are in a relatively new home that was built with higher end windows, new efficient windows will probably save you some energy. Unless you have very old and poor windows, that savings is likely to be small enough in comparison to the cost of a window retrofit job that it will take many years for your savings to break even with the expense of the job. The average payback period from energy efficiency savings on a window replacement job is 8-10 years.
“But I’m planning to sell my house. NOW should I replace my windows?”
If you are upgrading your windows with the idea of selling your home in the near future, you can expect to recoup about 80% of your investment in the form of a higher selling price. Of course, if you can do some or all of the work on your window upgrade yourself, your margins will be significantly more attractive.
All this does not mean that you should never replace your old and inefficient windows. It just means that there are probably other projects that will cost a lot less money with an equal or greater amount of energy and money saving potential.
Should I replace my windows? — Look for cheap or low cost paths to greater efficiency first
When it comes to energy efficiency retrofits always go after the low hanging, easy, and inexpensive fixes first. Projects such as air sealing in your attic, ventilating your attic, sealing HVAC duct work, and upgrading your lighting to CFL or LED will cost very little and may save a bundle.
Projects such as upgrading your attic insulation with loose fill cellulose, adding insulation to a crawl space, or replacement of inefficient cooling and heating equipment will involve a bigger investment, but are likely to have a shorter payback period than window replacement.
Once the easier and cheaper projects with a good energy saving payback have been undertaken, tackle that new window project. Every BTU or kilowatt you save is good for your wallet and for the planet.
“But my double paned windows are foggy between the panes…NOW should I replace my windows?”
A thin film of water condensation between the glass of a double pane window is a common problem. On most new windows, there is an inert gas such as argon between the two panes of glass. These gases have greater density than air, providing resistance to small convection currents in the dead space between glass panes.
Over time, the seal on one of the panes or on the window frame itself can develop a small leak, causing the gas to leak out and be replaced by room or outdoor air. The moisture in this air can condense on the cool exterior window pane during cold weather or on the interior pane when the air conditioning is on in the summer.
While window marketing will tout the insulating properties of rare gases used between panes, some energy experts suggest that these gases actually make only small improvements in thermal resistance.
Condensation between panes is largely an aesthetic issue. If you change your windows for this reason alone, you will probably never save enough money from the additional energy savings of an intact gas charge between panes to equal the expense of changing these windows.
Should I replace my windows because I don’t like the film on them? might be a better question. Aesthetics may be an adequate reason to opt for replacement of the glass panes, but probably not the whole window.
“But my windows weep condensation on the inside. NOW should I replace my windows?”
A thin film of water condensation between the glass of a double pane window is a common problem. On most new windows, there is an inert gas such as argon between the two panes of glass. Over time, the seal on one of the panes or on the window frame itself can develop a small leak, causing the gas to leak out and be replaced by room or outdoor air. The moisture in this air can condense on the cool exterior window pane during cold weather or on the interior pane when the air conditioning is on in the summer.
Condensation between panes is largely an aesthetic issue. While some window marketing will tout the insulating properties of rare gases used between panes, these gases actually make relatively little difference in thermal resistance. The R-value lost by leaking gases is, in fact, negligible. If you change your windows for this reason alone, you will probably never save enough money from the additional energy savings of an intact gas charge between panes to equal the expense of changing these windows.
You may find the condensation film unsightly, which may be an adequate reason to opt for replacement of the glass panes, but probably not the whole window.
“Okay, so when SHOULD I replace my windows?” –- Get an Energy Audit to know for certain…
The only way to get a full appreciation of payback intervals for the various energy retrofit projects you might have in mind for your home is to get an energy auditor to do a comprehensive evaluation of your home.
Look for an energy auditor who is certified by the Building Performance Institute or by RESNET, and preferably from an independent company and not a contractor.
It’s funny how an audit from a window contractor will almost always recommend window replacement, while an audit from an insulation contractor will recommend that you add their high-end spray foam to everything. Hey, when your only tool is a hammer, the whole world looks like a nail!
Hiring an independent energy auditor will give you a true evaluation of your home, not a sales pitch.
An Energy Auditor Will Know About Incentive Programs
Your auditor will also be able to advise you on available federal and state tax incentives, utility and state rebate programs, grants, and low interest loans.
A little guidance and data will make it all clear, and who knows, you might just get those new windows out of the deal after all.