PS--- the height of the sidelights are about 79 inches tall-- so, of course, not standard size;)

I would consider an insulated film which wouldn't take away from the looks of the windows. There are many options for your decor. Not sure a curtain, unless backed would do what you need. A film would also allow light in during the day. Privacy at night is an issue though.

Curtains will only help if there is a draft through the window framing, and that should not be happening in new construction. There are tests you can do to see if there are drafts, one as simple as holding a candle near the perimeter of the window and seeing if the flame moves. If you do, you need to get the builder back out to fix the problem.

It looks like you have a basement under the entryway, so the cold should not becoming from the flooring.

Maybe you need to play around with the dampers (if you have them) or the registers. The dampers would be near the furnace, and they direct the airflow from the furnace.

Tension rods and sidelight curtains are unlikely to help. Thermal drapes are what are used to block airflow at windows.

I'd do as graywings suggests and check out the heating system. I live in Canada in climate zone 3 and my house is never cold unless I turn the thermostat way down when I go away.

I'd also put a nice thick area rug on the tile floor. Tile floors and cold climates don't go together in the winter IMO unless one has in floor heating.

Your entry space may always feel cooler than the upper living areas tho as the thermostat is likely on the LR level and heat rises so the temperature will always be lower at the entry level. I've lived in houses with a similar style and unless you have more than one thermostat that's just the way it is. If you have the option of running the fan constantly it may move the warm air around and be warmer in the entry but, of course, that will eventually wear out that fan. I use that option occasionally when I use my wood stove which more than adequately heats the upper floors but heat doesn't sink so my basement areas are cold unless I use the whole house fan.

IMO curtains won't help altho I've heard of people making drapes from quilts or blankets (which can look quite nice) to keep a room warmer in the winter. However IMO all that does is block air circulation to the windows and cause moisture build up which leads to mold. Not what I'd want.

Your entry will be nice and bright with all those windows and since you really only pass thru that area and don't actually 'live' in it I recommend doing the minor fixes and ignoring the cool.

Enjoy your new home and don't expect perfection. I've lived in many houses and even the ones we planned and had built were never completely without small flaws. It's kind of like life - can be enjoyable but it's rarely perfect.

Yes -- check for drafts around the windows and the doors -- there are many ways to add additional insulation -- just ask at your local home center ....do check the insulation in the ceiling of the basement too (if you have one under the entryway)

Plus add a long wide sisal rug to the entryway (works for both the look and the texture) -- check around for indoor-outdoor ones -- and you could even take it outside to a patio in the warmer months.

IF this problem continues -- you may have to add a thick lined single curtain (or a pair of lined panels) across the entire doorway (and windows) This is called a "portiere" -- and is one of the oldest ways in decor history to stop a drafty doorway. You would have to install a curtain rod across the height of the top window -- and simply close them as needed ....

One of the problems is that your entry is in the middle of an open "chimney" -- any warm air there will rise to the upper floor. Is there a way to add a portiere to the top of the staircase, or is it open plan?

Some of the homes around here have ventilation systems that take the air from the ceiling of the upper floor and vent it on the bottom floor, to reduce the stratification. If there is a simple way to do this, it might be your best bet -- have the intake in the ceiling at the top of the stair and the outlet at the floor at the bottom.

The door doesn't look particularly special so it may not be insulated and it may not have weather stripping. If the glass is single pane, it will also be cold. You can look into shrink wrap plastic that is used for windows to act like storm windows...not sure what shapes and sizes it comes in though. I would also be sure to put down an area rug...polypropylene to take the wear and tear...to make the floor warmer. Also check for caulking around the exterior of the window to make sure it is sealed properly.