Blackout curtains help to keep light out, making them useful if you have a lot of light pollution at night or need to sleep during the day. But do blackout curtains help with heat? Do blackout curtains save energy? And how much?
Blackout curtains can have an R value of up to 5, depending on how you use them. Considering most windows have an R value between 1 and 5, and your walls have an R value of at least 13, blackout curtains do help with heat, and can save you hundreds of dollars per year.
How blackout curtains help with heat
Blackout curtains block light, which can also help block heat in the summertime. But the backing on blackout curtains has insulating properties too. This means they help to keep the cold out during the winter months too.
How much insulating properties blackout curtains have depends both on the curtains and how you use them. Ideally, when you buy curtains, buy curtains that advertise thermal properties as well. If the curtain tells you its R rating, even better. Buy the highest R rating you can find.
To get the full effect, you need to attach the curtains to the wall to seal out the window. The best thermal curtains come with Velcro strips for exactly this purpose. During the hottest and coldest months of the year, you seal the curtains to the strips to seal out airflow and improve the curtains’ insulating properties. During warmer months, and on unseasonably warm days, you can unseal the curtains so you can use them as normal.
They’re a good choice if you happen to be renting. You can’t change windows in a rental property, of course. But you can replace the curtains. And when you move, take your curtains down, put the original curtains back up, and take your blackout curtains with you to use in your new place. Even if you don’t install the Velcro (which I recommend not doing if you’re renting), the curtains will still help, just to a lesser degree. And they make the room more comfortable because it feels less drafty.
The effect of windows on heat and why blackout curtains can help
An uninsulated wall has an R value of between 1.0 and 1.5. A single pane window has an R value around 1. A good double pane window has an R value of 4-5. A triple pane window could have an R value of 9. A properly insulated exterior wall should have an R value of at least 13.
As you can see, there’s a big gap between the properties of an insulated wall and any windows the wall may have. There’s enough difference that any window that’s less than a triple pane might as well be slightly open all the time.
Replacing single pane windows with double pane windows will save you between $126 and $465 a year, according to US Department of Energy estimates. This is where the value of good curtains shines.
The cost of new windows varies. Despite what the billboards say, there’s not really any such thing as a $189 window. But for estimation purposes, let’s say it costs $200 per window to replace them. Good curtains will give you a similar effect, but a set of thermal or blackout curtains may only set you back $20 per panel. So you’re talking $40 per window, or about 20 percent of the cost. Tax credits on energy efficiency may close that gap a bit, but they vary from year to year.
It’s a lot easier to come up with $40 for a set of curtains. And if money is tight, you can do one room at a time as you can afford it. If you only replace one window at a time, you’ll spend more per window.
Even if the savings are on the low side of the estimates, along the lines of $100-$200 per year, good sets of curtains pay for themselves pretty quickly.
Do blackout curtains save energy if I already have good windows?
Even if you have new, energy efficient windows, a good insulating curtain can make a lot of sense. If you have triple pane windows, which is about the best case scenario, your windows have an R value around 9. Your walls are probably at least R-13 if you have good windows. Installing thermal curtains and insulating blinds helps you close whatever gap you have in insulation between the wall and the window. The curtains will probably save you $100 a year, and they last a long time if you take care of them. Take them down to wash them about once a year, then hang them up to air dry. That’s usually all they need. I still have some thermal curtains I bought 10 years ago.
By installing good thermal curtains and taking other measures, I’ve been able to decrease my energy costs most years over the last decade. Energy hasn’t gotten any cheaper, but by using less of it, I’ve been able to negate the increases. That’s good for the environment and good for my wallet.