Thermal insulation influencing factors

The insulating properties of the windows

Not all windows offer the same thermal insulation level. Older ones, with cracked wooden carpentry and with only one layer of ordinary glass will always provide less insulation than modern windows with double panes made of LowE glass and filled with an inert gas, usually Argon, with silicone sealing and with frames organized in chambers that help providing superior thermal insulation. Some manufacturers went even further, so even triple glazed windows are available for those who need superior thermal comfort. If you have such a modern type of window and you add a thermal curtain to it, you probably won’t feel too much of a difference. However, if you add an insulating curtain or drape to an old window, you won’t need measuring instruments to tell you that the thermal resistance of your window has significantly improved.

Other window treatments

Cellular window blinds or insulation shutters have a positive effect in preventing thermal exchanges at the window glass level, therefore they may be just enough for an efficient insulation, thus making insulating curtains redundant.

Windows orientation

If your windows are orientated towards North, they will be less exposed to direct sunlight, therefore those rooms will always be colder than rooms which have the windows facing South.

R-value and u-value

The two parameters most commonly used to express thermal insulation are the r-value and the u-value. Usually, windows manufacturers and retailers state only one of the two values on their products. Let’s see why and how the two parameters are in relationship, so one of them is enough to define the thermal insulating properties of a window or door.

R-value = the expression of how much an insulating material resists heat passage through it (a measure of the energy conserving capacity of a material). The better insulator a material, the higher its R-value.

U-value = the expression of how much heat is lost because of passing through an insulation

This leads to the following relationship between r-value and u-value:

“r-value” = 1/”u-value”

A single-glazed window often provides an R-value equal to 1. By simply replacing it with a double-glazed one, the R-value will double. By adding a lined thermal curtain to the single-glazed window, one could hope to obtain an R-value of about 1.2 – 1.4. Although it may not seem much, the comfort in the room will significantly improve, not because of the r-value improvement, but because the thermal curtain will stop the draughts which are the real discomfort generators. However, for this to happen, it is important to properly install the thermal insulating curtain, which means that it should be mounted tight against the wall on all three free edges. Another important issue is that a thermal curtain should never cover a heat radiator, because that would make your room temperature even worse than it was before, as heat from the radiator will be prevented to advance towards the center of the room. Many times, simply stopping the draught offers direct and perceptible benefits to the user, therefore if the household budget doesn’t allow for installing windows with high energy efficiency, a carefully done weatherstripping of all windows and doors in the house may give good results as well. It’s actually the cheapest way to get thermal insulation for your home.

Making cheap insulated curtains

Making your own insulated curtains is easy. You only need to buy the insulating, reflective layer of fabric, then sew it on the back of your curtains. If you don’t have money to buy that special insulating sheet, you can go creative and use some old duvet instead, or some cheap aluminum foil. After you obtain the lined curtain, you need to work out a way to attach it to the wall on the sides and on the bottom edge. Velcro stripes are cheap and effective: just sew one side to the back of the curtain and stick the other side on the wall.

Thermal drapes for children’s rooms

Many people are concerned with thermal insulation when it comes to children’s rooms. That’s understandable, because children are more sensitive than adults and if they get ill, the money spent on doctors and drugs may exceed the budget needed to properly insulate their windows and doors. It would be very nice of parents could make an financial effort and buy good windows for a child’s room. However, if they can’t do that, just sew an insulating lining to the back of the drapes you already have. Additionally, buy some sealing strips and install them at all windows and at the door bottom. Another thing you can do is to avoid placing the child’s bed under the window. Try to use that wall for some other piece of furniture, or leave it alone, but don’t place the bed there, because the child will be exposed to cold draughts at night.

The first step in making a thermal curtain is measuring your windows. The curtain should be bigger than the windows, in order to provide an efficient insulation. Allow a few extra inches to the left and to the right, as well as at the bottom. There’s no need to have it touch the floor. In case you are not making the curtain from the scratch, but only lining an existent one, take it off the window and measure it, as the lining needs to be almost the same size – you can make it about one inch smaller, in order to avoid it becoming visible when hung at the windows. Here are two options: one is faster, but leaves the outer side of the curtain a bit uglier, as the seing will be visible. The other one is nicer but requires more attention when sewing: you first sew three edges, then flip the curtain and only then sew the final edge. In this way, the first three will be looking very nice and well finished. For the first case, the lining needs to be a bit smaller than the curtain, while for the second option, the two of them need to be exactly the same size.

The lining material with insulating properties can be found as such in home and garden stores, so you’ll have to buy it.

Cut the lining with great care, so it fits the curtain, then sew them together. Start with the top of the curtain, then sew the other edges. For the best result, it would be ideal that you use pins to fix the two fabrics together, then see if you did it correctly, and only after that proceed to assembling them together.

For optimal energy efficiency, your thermal curtains need to be attached to the walls, not only to the curtain rod. If you allow gaps between the curtain and the wall, there will be drafts that will push cold air inside the room. An excellent and very cheap way to fix the insulated curtain against the walls is Velcro tape. Another idea is to sew magnetic straps inside the lateral edges of the curtain, then have metallic straps attached on the walls. I don’t know how much this costs, but it can’t be as cheap as Velcro.

In order to be more clear, let me tell you that the R-value is a parameter which defines the thermal insulation efficiency. An R-value of 1 is very poor, and that’s exactly the case of single glass pane windows. So, if you have such windows and you don’t have enough money to replace them with double glass panes, low-e ones, or to add another set of windows on either the interior or the exterior side, you could consider investing in insulated curtains. These are probably the cheapest window coverings with insulating properties.

Thermal curtains won’t make your rooms look strange, as they are just like any other window covering, but features additional thermal insulating properties. The lining has a major contribution to preventing the temperature change between the room air and the cold window glass. Another factor that matters is the fact that such curtains are fixed at both their top and bottom edges. As the cold air is heavier than the hot air, it tends to escape through the bottom end of the curtain, therefore this seal plays an important role in providing the thermal insulation.

In future articles, I’m going to detail more on the types of fabrics and linings used for thermal curtains, on how to make your own insulating curtains and on where to buy them, in case you don’t like sewing that much. I’ll also try to seek for coupons and promotions from retailers and stores and I’ll publish them here, in a special section of the site.