Carbon at the point of entry is the stage that takes chlorine out of every tap and shower rather than just the kitchen, and it is the one most often undersized, because the constraint is not what the media can do but how long the water spends touching it. Getting that right decides between a system that works and one that is bypassed in frustration.
Contact time is the whole specification
Carbon works by adsorption, and adsorption takes time. A cartridge rated at a generous flow will pass that much water; it will not necessarily treat it at that rate. The same element performs far better at a slow tap than on a whole house line during a shower. So the specification question is how much media the water passes through at your peak simultaneous draw, which is why whole house carbon is usually a large housing or a media tank rather than the cartridge that fits under a sink.
Cartridge housings against a media tank
A large diameter housing with a twenty inch carbon block or granular cartridge is simple, cheap to install and suits moderate demand, with cartridges replaced on throughput. A backwashing media tank holds far more carbon, gives much better contact at household flow, and backwashes to prevent the bed packing and channelling, with media replaced every few years instead of cartridges every few months. The tank costs more up front and less to run, and it needs a backwash flow the supply can sustain.
Chloramine changes the answer
If your utility uses chloramine rather than free chlorine, standard carbon reduces it slowly and incompletely, and a system sized on a chlorine rating will under perform. The media has to be catalytic carbon and the contact time has to be substantially longer, which in practice means a larger vessel or a slower flow than the same house would need for chlorine. Check the utility's annual report before specifying, because this single fact changes both the media and the size.
What it changes and what it does not
Every tap and shower loses the chlorine smell and taste, which is the point, and downstream equipment including softener resin and any membrane is protected from chlorine attack. It does not soften water, so scale continues exactly as before, and it does not remove iron, nitrate or dissolved salts. One consequence worth knowing: removing the disinfectant residual means the water inside the house plumbing is no longer chemically protected, which is a reason to keep the media fresh. Our installation guide covers the train.
Questions people ask about water carbon filter system
What decides how well a whole house carbon filter performs?
Contact time at your peak flow, which means media volume rather than the cartridge's stated flow rating.
Cartridge housing or media tank?
A large housing suits moderate demand and is cheap to install. A media tank gives far better contact and lower running cost.
Does chloramine need something different?
Yes: catalytic carbon and substantially more contact time. A system sized for free chlorine will under perform on chloramine.
Will it stop limescale?
No. Carbon does nothing to hardness, so scale continues exactly as before. That needs a softener.