Replacing old windows in all but the most extreme cases will not save money in your lifetime. Repairing old windows or adding layers may be a more cost-effective solution.
We often get asked if it is a good idea to replace old windows with new and better performing windows to save money. Usually to the surprise and relief of homeowners we most often tell them to stick with the ones they've got. Not to say that the idea of replacing windows is always 'green washing', but it's not necessarily going to save energy and money once you run all the numbers.
Yes, old windows will leak more air and lose more heat than new ones, but there is an energy variable to consider with replacement as well. Purchasing a new window will have its own energy footprint in terms of raw material extraction, manufacturing and transportation.
The cost of replacing windows is pretty high and predominantly labour based; partly in manufacturing, but you have to factor in the cost of installation and finishing as well. So if you're going to replace them, you might as well get good ones. To go to all that effort and install a low-quality double-pane window doesn't make sense from a financial point of view, or even quality of life.
Upgrading a potential purchase from double to triple pane usually means an additional 20-25% on the sticker price, and there is a relatively quick payback on that added investment that comes from energy savings if in the end you are going to buy some. Beyond energy savings, a triple pane window offers greater durability, reduced sound transmission and a noticeably more comfortable home on cold days. All that is to say, if you are buying windows for any reason, buy good ones.
Will replacing old windows save money?
The short answer is, it's not likely. From a standpoint of saving money, a complete home window replacement job rarely justifies the cost. For full disclosure before we do 'our' math, we don't like vinyl and we would only ever install triple pane windows with Low- E coatings and wood or fiberglass frames.
A truly accurate assessent of whether or not you should replace windows would take a quote of the windows you want and possibly energy modeling of your existing winodws and potential new ones to see how far out your payback period would be be, but to quickly do your own very rough guesstimation - imagine the cost of a good quality triple pane window of perhaps 4x5 feet; call that about $1,200 for arguments sake. Now add installation and finishing costs - we'll conservatively call that $400 to install, insulate, and replace trim inside and out.
Now look at your heating bill and figure if it is even possible to recoup the replacement cost of a window through added energy savings from that individual window. How long will it take to save $1,600 worth of heat through a better window, and will you even live that long? In most cases it is unlikely that you will be around to see a return on your investment. The window itself most likely won't last as long as it takes to recoup the money before needing to be replaced again.
When to replace windows:
If your windows are extremely damaged by water infiltration you have a strong case for replacement. Letting rot go unchecked in your house will just lead to further problems. More than just the loss of heat, money and comfort, over time rot could spread beyond just the window and affect the structural integrity of the wall itself. There is also air quality issues to consider as you may have mold and mildew as well. In such a case you may be wise to replace an individual window.
The problem here is of course the 'slippery slope', in that replacing only one window on a wall may stand out, and replacing the windows on only one wall of the house may stand out. That's unfortunately your own demon to chase off; we can't help much there.
Repairing old windows:
If your frames are in relatively good shape and the issue is air leakage, repair is not only possible, it will likely be much cheaper and offer a very quick payback for your efforts in terms of saving energy and money.
Air tightness - air isn't moving through the glass, it’s leaking around old seals and perhaps between the window frame and rough opening. If you can stop that from happening you have stopped your air leaks, so having airtight windows may be only a tube of caulking away.
The first step would be determining from where exactly air is leaking. Keep in mind the natural stack effect of buildings - warm air rises, so in the absence of wind pressure air will leak in on the bottom floors and leak out on the top floors, so it may be a little tricky to identify leaks from the inside on upper levels. A cold windy day may help you with your forensics, also look for signs of moisture damage like water staining, mold and mildew.
How to fix fogged windows:
Over time, the seals in windows start to wear down allowing air to leak in and out, in some cases this leads to windows with humidity between the panes. There are companies that offer a service of defogging windows, often for about half the price of replacement. This is a solution where we are quite suspicious of the assessment of savings and final quality.
To repair a fogged window, holes are bored in the glass to facilitate cleaning them, moisture venting valves are then installed in those holes to make sure air can flow through and remove moisture in the future so the problem doesn't reoccur. This creates a convection loop in between the panes, so after a repair, a double-pane window may perform more like a single-pane window. While they may be nicer to look through, they may perform worse than they did before the repair so don't look at this as an energy and money-saving solution.
In the long term, the added heat loss with de-fogging in our opinion negates the proclaimed benefits of this repair solution. We would instead recommend at that point to consider replacing the thermals, which are the sealed glass units inside the frames. The thermals of double paned windows have a lifespan of about 20 years, so it is fairly normal to have to replace them.
Replacing window thermals is often an option, that's done without having to remove and change the entire window, you just remove the trim on the inside of the window (whether it is fixed or operational) to access the thermals, which are the sealed glass units inside the frame.
This is initially more expensive than the defogging but cheaper in fairly short order due to energy savings, and it's a good time to upgrade to gas-filled chambers and Low-E coatings, even ones with a third pane if there is room for the added thickness.
What the best solution is will depend on the initial state of the windows you are considering replacing. Some questions that should be asked and answered - how leaky are they; are the frames in good condition; are the frames insulated and do they have Low-E coatings?
If in the end you decide to replace your windows or you're buying some for a new build, check out some of the following pages. Windows are not all created equal, choosing the right ones and a proper installation will have a huge impact on how they perform and how long they last.