What is the best method to paint steel door frames when it's already installed in a occupied home ? I have alumn. Frames:confused:

Spray gives a smoother finish but overspray mau be an issue since the house is occupied. You may need to stick with a trim brush. I add Floetrol to the paint to get it extra smooth. Latex Paint Additives | Latex Paint Flow | Flood

How about using a foam brush

You can use one but it is less effective than a trim brush or spray. Why would you want to. Convenience?

I think using a foam brush you will not have any brush streaks

Brush strokes are caused when too much paint is applied and the paint is viscous, thick. Add Floetrol and use a brush. Its your call but I am just telling you how we do things. There is no hard and fast law/rule about paint, just best practices.