From Thermotech's website: Firstly a double hung window is not as air tight as a casement window. The double hung window has to slide, so its weatherstripping can't be as tight as a casement or it won't slide. That's obvious to most people. What is not so obvious is that sliding windows aren't as air tight as casements because the weatherstripping changes plane. Think of the bottom sash of a double hung. The bottom and side rails are weatherstripped along the edge of the rail. But what about the meeting rail? It's weatherstripped along the outer face. It is difficult, very difficult, to maintain the integrity of the air seal through this change of plane. Despite the fact that double hung windows are inherently draftier than casements, this does not have a major effect on your annual heating bill. The reality is that as long as new windows can maintain their tested air tightness (this topic will be the subject of a future column) very little of the window's heat loss is due to air leakage. Most of the annual heat loss from reasonably tight windows is from conductivity losses through the frame, spacer and glass. This is where double hung windows really fall down, (so to speak). All sliding windows have inherently cold frames compared to hinged windows, like casements. The sash in a casement window is "insulated" on the inside by the hardware cavity. The sash in a double hung window has no such advantage. Another inherent thermal weakness in any sliding window is the meeting rail. Thermally it is the weakest part of any sliding window. The upper sash in a double hung not only loses heat through its outer face, but also through its lower edge. It is cooled on two sides. That's why the bottom edge of the upper sash experiences condensation before the lower sash.

Only problem with that solution, is that if the unit is a double hung, the upper sash will be able to be pulled down. Your options are limited, because you need to keep the egress in tact. You don't mention how old the child is or what type of windows you have, but here's what I've done: On some old wood double hungs, we positioned the sash to the spot we wanted them to lock, about 4 inches of opening. We then drilled 1/4" holes through the lower sash into the upper sash. Our sash were 1-3/8" thick, so we drilled 2-1/4 inches. Then we took 2 old hinge pins and slid them into the holes, locking the sash together. To restore full operation, simply pull the pins. This will not work with modern clad windows, as you'd be drilling through the cladding. That will void warranties. Many hollow vinyl windows have a pop out tab on the upper sash that will limit the opening to a few inches. Being a parent myself, I'd probably keep the window locked and install central AC or a wall mounted unit if I had any concern for safety. Besides, if someone wants in, they will come in. With the window locked, an alarm could be installed. They have some small window alarms that don't require a whole house system. It's worth the piece of mind.

Eagle customer service is just ok compared to other manufacturers. I recommend to my customers Marvin or Jeldwen Custom. The service for both is great.

They are Innotech, a Canadian company. We are still under construction, so this is about the best photo I have. We were looking for triple pane windows with good seals anyway, so that's probably why our cost comparison was in the same ballpark. I think it's the general impression in the industry that T&T are a lot more expensive, but nobody seems to want to verify that. There was one kinda shady salesman from another company. All my other quotes were specific, listing the exact windows and the total price. This guy just said "$25-30k" for casements. And he wouldn't get specific until we agreed to buy from him. And then he was calling me daily to push me to sign up with him. I finally told him we'd decided to go with T&T, and since he wasn't supplying those, we wouldn't be buying from him. So then he said he could get T&T, but it would be "about 50% more". Given that his price was already about the same as the T&T guys, I was pretty certain we still wouldn't be buying from him, but I told him to go ahead and send me a quote. He never did, he just kept telling me that they cost more, and most people don't buy them because of that. Maybe because he doesn't specialize in them, he doesn't get good pricing on them? I finally had to block the guy's number. Durabuilt is another Canadian company that was in the same ballpark as Innotech.