Want to hang draps in my living room with a heather below window sill

No idea what you're taking about here. Can you explain a bit what your issue is m

I would guess that the thing under the window gives off heat... perhaps a radiator if the house has hot water or steam heat. All the windows in my house are like that. You can hang drapes on the wall next to the heater and hang blinds or sheer curtains over the actual windows. Blinds will hide the edges of the windows better than sheers will

If it is a floor heater vent, your local home improvement store carries diverters. They are magnetized and sit right on the vent and direct the air forward instead of up inside your curtains.

this should not be a issue..hang them above the heater

Usually advised to have any fabric 6" away from a heater. So shorten them, or use curtain tie backs and extend your rods past the window frames.... https://www.google.com/search?client=opera&hs=Ngq&ei=gu1zWvb9NM7kjwPC76qYAw&q=curtain+tie+backs&oq=curtain+tie+backs&gs_l=psy-ab.12..0l10.226311.234309.0.238264.13.9.0.4.4.0.151.1148.1j8.9.0....0...1c.1.64.psy-ab..0.13.1192...0i67k1j35i39k1j0i20i263k1j0i20i263i264k1j0i131k1j0i131i20i263k1.0.y4Q2pD_9t08

This is no problem. I have drapes and sheers . I have them down to the floor. It is about 25 inches below the window. This is not a problem.

Do you feel that the heat is trapped behind the drapes in the winter time in DE? I have electric heat in one room and have my blinds end just above the heat register.

Having a large radiator under a large window is what made us decide to use shutters in our living room. We also constructed a cover for the radiator which also allows the heat to "escape" Since we have bookcases that encircle the living room, we had no room for curtains to be hung on the sides.