Match the filter to the claim
NSF/ANSI 42 covers aesthetic claims such as chlorine, taste and odor. NSF/ANSI 53 covers specific health-effect reduction claims. A product certified to one standard is not automatically certified for every contaminant within that standard.
Do not ignore service flow
Whole-house media can create pressure drop. Compare the manufacturer's service-flow and pressure-drop data with your household's expected peak use.
Maintenance is part of the system
Include replacement cartridges, media life, backwash requirements, drain needs and bypass access in your plan.
Next step
Run your numbers through the Water System Planner, then verify any product against its actual service-flow, pressure-drop, capacity and certification data.