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A: In a hot climate you need to keep the heat out. In a cold climate you need to keep the heat in. The answer is the same in either climate: insulation and triple-glazed windows. There are examples of how much money you can save by installing double and triple-glazed windows in the book in chapter 3. In more remote places like Australia, the choice of windows is often less than we have in the US or EU. This often makes triple-glazed windows hard to find. I even found it hard to get them in the US, my windows came from Canada. If you cannot get triple-glazed windows I suggest looking for the best low-E double-glazed windows. If you use a low-E 272 coating on the outside and a low-Ei89 coating on the inside you will get about R4 insulation with only the slightest greenish tint. This is as good as a triple-glazed window with i89 on the inside.

A: No. We have R4 triple-glazed windows on the lower floor and R5 on the upper floor. They are completely clear to the eye. There are photographs of four different types of low-E glass in the book in chapter 3, so you can see exactly what they look like.

A: The optimal air gap is about ½”. This is supported by both academic research and experiments I did on my own with small double-pane windows that I made in varying thicknesses.  Almost all double and triple-glazed windows use this spacing. If the spacing is larger the ½” the insulation value goes down because then convection currents start to move the heat from one side to the other. 

A: No because I have not added exterior storm windows. However, the purpose of exterior storm windows and interior-fitting window inserts is very different. Exterior storms protect the window frame and its paint from wind, rain and sun. But the air between the exterior storm and the real window is not sealed and it blows away with the breeze, hence it has very little insulating value. With little insulation benefit there is very little cost saving with exterior storm windows hence the reduction in carbon footprint and heating bill is likely to be very small. The purpose of interior-fitting window inserts is to stop drafts, add insulation and block noise. Because they are very effective at blocking drafts (see Chapter 4 in the book) and adding insulation window inserts will both cut your heating bill and carbon footprint. The financial payback is about 5 years. The increase in comfort of the room is immediate.

A: there are several good options for you. Blinds are cheap and effective at blocking sun. Growing deciduous trees that shade the windows in summer are also very effective if you are prepared to wait the 5-10 years for the tree to grow. Adding window overhangs also works very well but they cost more to add. The sunblock films you can buy at hardware stores do work to cut down the sun’s heat. They are cheap so you can’t lose anything to try it and see if you like it.

A: No. The low-E coating gets added to the glass at very high temperatures in the factory. You can buy films to apply to the glass from the inside, but these are not low-E coatings (i.e., they do not selectively reflect either UV or IR light) but they darken the whole window. They are good for blocking intense sun but they do not reflect the IR light that keeps you warm in winter.

A: We open plenty of windows and patio doors in summer, or more commonly in the shoulder season when it is around 70F outside, just not the ones with the window inserts.

A: You can but I do not. I leave mine in year round.

A: Please see the evaluation I did of the window inserts from four manufacturers. It is in the “Stuck at home COVID19” edition of the book which is available for free from my website, use the code COVID19 at checkout. If it does not work email me.

A: Yes, but only if the window material is glass. The only maker of window inserts that I know of that makes them in glass is Innerglass in CT, all the other companies I tested were made from clear plastic.