Many of us are familiar with the ubiquitous advertising "deals" on thermal replacement windows. They tell us that replacement windows will save us money on energy and maintenance. They tell us our home will be cozier. They tell us our home will be more valuable. We wonder whether any of what they say is true. We ask questions and get some hi-tech double talk about low-E glass and argon gas. They might as well be talking Chinese.

So what is the truth about thermal replacement windows?

Here are straight answers to the most commonly asked questions about windows:

Q. What's the difference between the windows I have now and thermal replacement windows?

A. You may already have thermal replacement windows. The easiest way to check is to see if there is more than one sheet of glass between you and the outdoors. Thermal windows are always double- or triple-paned. Traditional windows are single-paned. Thermal replacement windows allow far less heat to escape your home in the winter and less heat to get in during the summer, lowering your fuel bills considerably. Most thermal windows also eliminate the need for painting.

Q. Do thermal windows really save enough energy to pay for themselves?

A. Windows and doors are typically responsible for about 40 percent of your home's heating bill. Thermal windows are typically two to four times more efficient than older single pane windows. That means you can expect your winter heating bills to drop on average about 20 percent to 30 percent. The bigger your fuel bills and the draftier your old windows, the quicker your new windows will pay for themselves.

Q. Are the telemarketing firms that call me scam artists?

A. Both legitimate firms and shady firms use telemarketing as a way to get business, so it's hard to generalize. Although telemarketing is annoying, it does not necessarily mean the company is crooked. Most telemarketers set up appointments for free estimates. Expect to be put under considerable pressure to buy during the free estimate. Never buy windows without getting more than one estimate. Whenever hiring any home service firm, use a contractor referral service or thoroughly interview references and check records with area consumer agencies.

Q. I've seen some pretty good deals on windows at a local home center store. Is that a good way to get windows?

A. Sometimes you can get a good price at a home center, but there are several pitfalls to watch for. First of all, the best prices are typically for "bargain" windows that may not be built well and may not last long. Second, it is difficult to get a pro to install windows you buy from a home center. Most pros realize that if something goes wrong and it is due to a shortcoming in the window, they will likely shoulder the blame. That means either you or a handyman will have to do the installation. If thermal windows are not installed exactly plumb and square, with all the appropriate insulation, you may get little or no energy savings.

Q. What is "low-E glass"?

A. Low-E glass has a special coating that blocks certain kinds of light that we can't see. The result is that it looks like normal glass but insulates better.

Q. What is argon gas?

A. Argon is one of the most popular gasses used to fill the space between the two (or three) panes of glass in a thermal window. Argon is a good insulator.

Q. With all the technical terms, how can the average homeowner make comparisons?

A. The best way to compare windows is to check for a rating from the National Fenestration Rating Council (NFRC). Most major brands of windows have a sticker on them that lists their NFRC rating. The lower the number the better. To achieve a low score the manufacturer has to build the window carefully and incorporate a variety of energy saving features.

Q. Are "maintenance-free" windows really maintenance-free?

A. Most thermal replacement windows are made of wood, vinyl or a combination of the two. Vinyl windows require no painting, inside or out. Windows are the most difficult and expensive part of any painting project, so by eliminating the need to paint windows, homeowners can usually save a huge amount of money. Switching to "maintenance-free" vinyl windows may cut your painting bills by 50 percent. Vinyl windows still have to be cleaned, so they are not completely maintenance free.

Q. Is it a good idea to buy one of the well-known brands of windows I see advertised on television and in magazines?

A. All the well-known brands make at least one line of highly rated windows. The problem is that the well-known companies may also make other lower quality lines of windows -- including some of the so-called bargain windows that are built to be cheap. This means that you have to look beyond brand name. Many contractors install what are called "no-name" windows. Actually, the windows have a brand, just a brand no one has heard of. If you are working with a truly reputable contractor, he is not going to steer you towards a bad window -- after all, his reputation is on the line. There are many well-made no-name windows that offer consumers bang for their buck.

Q. Is window replacement a big project?

A. In terms of dollars, it's a big project. Doing the whole house may run many thousands of dollars. However, the work itself is pretty straightforward. A whole house can be done in as little as a day or two, with little disruption to interior spaces and household routines.

Q. Given the high cost of windows, does it make sense to borrow the money?