I do not know the age/style of your house but pondering this issue myself I went on a tour of the neighbourhood (mine is pretty much all handsome single family houses built from about 1880-1910), both Victorians and Colonial Revivals mainly and what became readily apparent is that in virtually all cases (and in the house plan books from that period that I pored over), the tops of the windows line up but the bottom of the windows can vary.

This was not the case in special instances like an added sleeping porch or sunroom even if historic but for virtually every other window it held true. The effect was a very nice harmony to the design even if very unusual and asymmetrical.

So I would say that if you can keep the upper level of the window constant, varying the lower sill height will not be an issue at all and will definitely improve the view for everyone. Good luck!

Thanks. My house was built in about 1992ish. So its not that old.

The bottom trim on the sink window starts about 4.25" above the countertop. The trim is 2.25" wide and so the actual window doesnt start until 6.5" above the counter. I would like to make the new windows about 2-3 inches taller. or maybe have the trim on the new windows start right at the countertop?

here is an interesting thread on the topic http://ths.gardenweb.com/forums/load/kitchbath/msg010555316155.html

My new windows are going to flank my range though, not the sink. I am just wondering if they need to be the same height as the sink window, or if it would look OK to bring them down closer to the countertop?

I think it would look ok from the interior to have the window sills be a bit closer to the counters, but how does it affect the fenestration pattern on the exterior? Would the new windows look appropriate?

Another consideration is your outlet placement. I would have liked my rangetop-flanking windows to come closer to the counter, but outlets were required by code in about the same spot. I didn't have enough wall space for them unless they went horizontally under the windows. I suppose I could have found a way to install them just under the counter on the cabinet front, but I refused to start chopping up drawer fronts for outlets.

We ran the window over the sink right down to the countertop with a bumpout for plants. I love it. If I were doing any more windows over the counter, I would run them right down to the counter as well....more light and it eliminates a lot of the trim work and tile work, etc. for a much cleaner line.

Also I highly recommend casements, but esp over counters as double hungs are almost impossible for anyone besides Charles Atlas to open without serious contortions or stools and countertop sitting.

Thanks. I only have 1 other window on that side of my house and its on the 2nd floor so I dont think these windows will look funny.

I agree about casement windows. I think this is the perfect time to use them, but my husband hates casement windows. He wants double-hung since all the other windows are double hung. He is 6' tall and has no problem opening the window over the sink. I am 5'2" and have to climb up on the countertop in order to open the window. perhaps I'll chat about it with him some more.