Adding a whole house sediment filter to a house that never had one is a contained job, and the difficulty is rarely the plumbing itself. It is finding a position that satisfies four requirements at once, and checking a couple of things about the existing pipework before any pipe is cut rather than discovering them halfway through.
The four requirements a position has to meet
After the main shut off, so the whole house is downstream of it and the supply can be isolated. Before the water heater and any other treatment, so everything is protected. With clearance below the housing equal to a cartridge length, or the element cannot be withdrawn. And somewhere a leak does no damage and you can reach without a ladder. Those four together usually narrow the options to one or two spots, which is why the survey comes before the shopping.
What to check about the existing pipework
Pipe material and size, since the fittings and the housing ports have to match and an old galvanized run may be due for replacement anyway. Whether the main shut off actually works, because plenty do not until they are tested and a seized valve turns a two hour job into an emergency. Where the nearest drain is, for flushing after the work. And whether the run has enough straight length to accept a housing with unions either side without straining anything.
Doing the work
Isolate and drain the section. Mount the bracket first and hang the housing on it so the pipework is cut to suit the housing rather than the reverse. Fit isolation valves either side and, ideally, a bypass across them, which is the difference between a ten minute cartridge change and an afternoon without water. Use unions or push fittings so the housing can come out again. Then open slowly, purge air through a nearby tap, and check every joint by hand and again an hour later.
Expect a debris flush afterwards
Cutting into old pipework disturbs it, so the first water through will carry rust and scale, and the new cartridge will catch a season's worth of debris in its first days. Check it after a week rather than waiting for the normal interval, and be ready to replace it early once. Downstream aerators and appliance inlet screens are worth checking at the same time. Our whole house filter guide covers sizing the housing for the household's peak flow.
Questions people ask about sediment filter whole house
Where should a retrofitted filter go?
After the main shut off, before the water heater and any other treatment, with clearance below the sump and easy access.
What should I check before starting?
Pipe material and size, whether the main shut off actually works, where the nearest drain is, and available straight run length.
Do I need a bypass?
Not strictly, but it is the difference between a ten minute cartridge change and an afternoon with no water in the house.
Why does the first cartridge block so quickly?
Cutting into old pipework disturbs rust and scale, so the new element catches a season's worth of debris in its first days.