Yes, they should be the same length.

Definitely they should be one length.

If you have baseboard heaters below the window, I would think that 84" sheers that would be closed continuously would create a fire hazard. Although it would be more asthetically pleasing for them to be the same length, I would tend to use the shorter panels.

Almost all our windows have vents below. When I had long sheers on, the wall behind the sheer was cozy warm in winter, nice and cool in summer. The room, on the other hand, was the opposite. So they now all have short sheers. Except the dining room, where the sheers are long but tied back so they don't hang over the vent.

Can you post a picture or two?

It's hot water heat, so I don't think it poses a fire hazard. It's hard to take photos because of the sunlight, but here are a couple. I only have the long curtains on this window; haven't gotten around to the others yet.

Here's another pic.

Okay, great!

Now,

1.) I think you should swap out the drapery panels for ones that are A) longer, and hang them as close to the ceiling as possible: 84" for a 7' ceiling; 96" for 8'; and B) lined.

2.) The sheers should be the same length as the drapes.

3.) Hang both drapes and sheers from the same fixture, which'll be a double rod. They're very easy to find!

Here are some examples of hardware that allows drapes and sheers to be hung at the same height (disregard how far away they are from the ceiling, though!):

And here are a couple of infographics I think are pretty helpful:

I love the Internet. :)

Thanks! We're trying to work with the existing hardware until we paint and get new windows, but I do plan to install them higher later on. I'm using add-a-rod things for the sheers now.

These curtains are lined. I need to add back tabs before hanging the rest; I have tabs pinned on for now on that one set.

Looking at that guide, I wonder if we'd be better off with sheer/semi-sheer shades. Right now, the single sheer panel works because the curtains cover the sides of the window. If the curtains move to cover the wall, I'll need more coverage for the window itself.

You're welcome! You know, I didn't even realize there was just one sheer panel there now. I just assumed it was a pair...oops!

As for using shades instead of sheers, that would totally work, but it depends on what you're trying to achieve (daytime/nighttime privacy, light filtering, etc.).

Will your new window be the same size/style? And are you replacing the entire window, or just the sashes? I, too, am about to replace windows, so I have windows--and window coverings--on the brain right now.

Feel free to bounce any ideas off of me; I've had just about every curtain/blind/shade/valance on my windows at one time or another!

I didn't want a pair of sheers because of the ability to accidentally leave an opening. My goal is to let light in, while being able to change without closing the curtains. In our last house, we had wooden blinds (regular size) and honeycomb blinds. A couple of those were cordless and they stopped working after a while, so I'm not keen on cordless. I don't mind the continuous loop versions.

I'm intrigued by the idea of blackout fabric roman shades with sheer solar panels underneath, but that's not in the budget right now. (We're in the middle of a major kitchen remodel!)

My husband is OK with getting more sheers for the room now, and changing it up later on when we decide what to do. There is no room in the current windows to attach any type of hardware. Not even tension rods. Anything would have to be mounted outside, but we don't want to poke more holes right now.

Windows will be new construction windows, so the whole thing will be replaced.