Hi There
I'm about to build a new house and the builder wants to use United windows and Doors. I have never heard of them before. Should I be concerned using this manufacture.

The link to their warranty details is here:http://www.unitedwindowmfg.com/Warranty.html.
But a warranty is only as good as the company. And it seems window companies go out of business every day. Ask your installer to give you the history of the company. If they haven't been around for that long, then it is hard to tell. Two companies we deal with are Silver Line and Great Lakes. They have both been around a while and build quality products.

http://www.allaboutdoors.com
http://www.doorandwindowparts.com