Installation
How to install a whole house water filter
Quick answer
A whole house filter cuts into the main line after the main shutoff valve and before the water heater, mounted on its own wall bracket so the housing weight never hangs off the pipe, with a bypass valve and a pressure gauge on each side. Push-to-connect fittings turn this into a weekend job on copper, CPVC or PEX rather than a soldering job.
A whole house filter is a point of entry device: it treats every gallon that enters the house, which means its location in the plumbing run is not a preference, it is the decision that determines whether the rest of the installation works at all. Get the location and the support right and a cartridge change is a five minute job for the next decade. Get it wrong and the filter chokes flow to the whole house, strains the pipe it hangs from, or leaves half the fixtures untreated.
This page covers the mechanical installation: where the filter goes, what holds it up, and how to plumb around it so the house is never without water during a cartridge change. It assumes you already know which filter and which housing size you need. If you have not sized that yet, start with what size whole house water filter do I need, which is sized on peak flow rather than on household headcount.
Permit requirements and backflow prevention rules for point of entry plumbing work vary by city and county, and some jurisdictions require a permit or an inspection for a main line tie-in even when the work itself is straightforward. Check with your local building department before cutting into the main before doing the work described here.
On this page
Where does the filter actually go?
The filter goes on the main line, after the main shutoff valve, and before the water heater. After the shutoff means the filter can itself be isolated for service without having to shut off the street or well supply upstream of it. Before the water heater matters for a reason that has nothing to do with taste: sediment and scale that reach a tank or a tankless heat exchanger settle and bake onto surfaces where a filter downstream can never remove them again, and a tankless unit in particular depends on clean incoming water to avoid scaling its heat exchanger between descales.
On a well system, the filter goes after the pressure tank, not before it. Backwashing and cartridge-based equipment both need the steady pressure and flow a charged pressure tank provides, and plumbing a filter ahead of the tank exposes it to the sharp pressure swings of the pump cycling on and off.
If the house branches to an outdoor hose bib or irrigation line before the water heater, whether that branch goes before or after the filter is a local code and personal preference question rather than a fixed rule. Treating outdoor water adds cost and cartridge life burden for water nobody drinks, and many installers tee the irrigation line off ahead of the filter for that reason, where local code allows it.
What has to be true about the mounting before you start
A filled 20 inch big blue housing weighs considerably more than an empty one once water and a cartridge are inside it, and that weight has to be carried by a bracket screwed into a wall stud or a solid mounting surface, never by the inlet and outlet pipe alone. An unsupported housing puts a constant bending load on the pipe fittings, and that load is what eventually cracks a fitting or works a compression joint loose, usually discovered as a leak rather than as a warning.
Confirm the pipe size and thread type before buying fittings. A housing rated for one inch NPT ports on a three quarter inch line needs a reducing fitting, and mixing that up after the pipe is already cut is a frustrating way to lose an afternoon.
Why a bypass valve is not optional
A bypass assembly routes water around the filter entirely, either through a dedicated bypass valve built into some housings or through three ball valves plumbed around the unit: one on the inlet side of the filter, one on the outlet side, and one across the two ends. Closing the two filter valves and opening the bypass valve lets the house run on unfiltered water while a stuck housing is worked loose, a cartridge is sourced, or a leak is repaired, rather than leaving the household with no water at all until the filter problem is solved.
Gauges on both sides of the housing are the cheapest diagnostic tool in this entire category, and installing them at the same time as the filter means they are already in place the day the cartridge starts loading. A rising difference between the inlet and outlet reading, not a date on the calendar, is what actually tells you a cartridge needs changing. See how to change a whole house filter cartridge for the pressure figure that triggers a change.
Installing it, in order
- Shut off the main and depressurize. Close the main shutoff valve upstream of where you will cut in, then open a faucet at the lowest point in the house and let it run until it stops, which confirms the section you are about to cut is fully depressurized.
- Choose the cut point. Mark the pipe after the main shutoff and before the water heater, on a straight run with enough clearance above and below for the housing plus a wrench swing for future cartridge changes.
- Mount the bracket first. Screw the housing bracket into a wall stud or other solid backing before any plumbing is connected, so the housing weight is carried by the bracket from the first fitting onward rather than by the pipe.
- Cut the pipe and dry-fit the assembly. Cut the section out, then dry-fit the bypass valves, the housing, and the gauge tees in sequence without gluing or crimping anything, to confirm every piece lines up before a joint is made permanent.
- Make the connections. Push-to-connect fittings need no torch or solvent and are rated for potable water; sweat or solvent-weld fittings work equally well if that is the skill and tools on hand. Install the pressure gauges on the inlet and outlet tees.
- Install the cartridge and close the housing. Lubricate the O-ring lightly, seat the cartridge, and close the housing sump hand tight plus the quarter turn most manufacturers specify. Do not over-tighten a plastic sump.
- Open the main slowly and check for leaks. Open the main shutoff slowly rather than all at once, watch every joint including the bypass valves, and correct anything weeping before moving on.
- Flush before drawing water for use. Run a hose bib or an outdoor tap downstream of the filter for several minutes to clear manufacturing carbon fines and trapped air from the new cartridge before anyone draws water at an indoor fixture.
Housing size decides how much flow gets through
The housing family, not the brand, decides the cartridge diameter and the flow the filter can pass before it becomes the bottleneck for the whole house. A standard 2.5 inch housing on a whole house feed is a common and preventable cause of a pressure complaint people blame on the water main instead of the filter.
A 4.5 by 20 inch big blue housing passes up to 15 gallons per minute, roughly twice a standard 2.5 inch housing on the same cartridge count.
Published figure A published standard, regulatory limit, unit conversion or manufacturer specification. It does not change because somebody disagrees with it.
| Housing family | Cartridge size | Typical maximum flow |
|---|---|---|
| Standard 10 inch | 2.5 x 10 in | 6 gpm |
| Standard 20 inch | 2.5 x 20 in | 8 gpm |
| Big Blue 10 inch | 4.5 x 10 in | 10 gpm |
| Big Blue 20 inch | 4.5 x 20 in | 15 gpm |
Match the housing to the peak flow your fixture count actually demands, not to the smallest box that fits the available space. See what size whole house water filter do I need for how to work out that peak figure.
What you need on hand
Pentair Pentek 150233 Big Blue Filter Housing, 1 Inch NPT, 20 Inch
$68.15The reference big blue housing in the 20 inch length with one inch ports, sized for whole house flow rather than under sink use.
Best for: A whole house installation on one inch plumbing
Check price on Amazon
Pentair Pentek 150578 MC-1A Mounting Bracket Kit
$13.22A wall bracket that carries the housing weight so it never hangs off the pipe.
Best for: Any housing installation, because an unbraced housing loads the pipe
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SharkBite Max Water Filtration Connection Kit, 3/4 Inch
$21.49Push to connect fittings sized for a filtration tie-in, which is what makes this a weekend job rather than a soldering job.
Best for: A first whole house filter installation without a torch
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Measureman Water Pressure Test Gauge, 3/4 Inch Hose Thread, 0 to 200 PSI
$16.17A pressure gauge that threads on directly, useful both for the inlet and outlet tees and for a first house pressure check.
Best for: A first pressure check before sizing any filtration
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Cash Acme EB45 Pressure Regulating Valve, 3/4 Inch
$62.42A pressure regulating valve worth installing at the same time if incoming pressure runs above about 80 psi, since high pressure strains a new housing the same way it strains everything else.
Best for: A house measuring above about 80 psi at the hose bib
Check price on AmazonHow we chose
We did not test this equipment in person and we never claim to. Picks are researched from manufacturer specification sheets, published standards and regulatory limits, and the recurring themes in verified owner reviews. Every pick is matched to a real grain capacity, a real micron rating, a real certified claim or a real flow rating rather than to a price bracket, and it is placed in the tier where its published capability actually belongs. We rejected the unbranded flood that dominates several of these search results, because a softener is a pressure vessel on the main line and a filter is the only thing between a contaminant and a glass of water, and neither is a place for a product with no parts channel and no service path. Where a figure is trade convention rather than a published standard we label it that way, and where a manufacturer does not publish a figure we leave it out instead of estimating it. Above all, we do not recommend equipment for a problem nobody has measured.
Frequently asked questions
Do I need a permit to install a whole house water filter?
Sometimes. Point of entry plumbing work that ties into the main line falls under plumbing code in some jurisdictions and is treated as routine maintenance in others, and backflow prevention rules for a main line tie-in vary by city and county as well. Check with your local building department before cutting into the main, since the requirement is genuinely inconsistent across the country.
Can I install a whole house filter myself without soldering?
Yes, on most residential copper, CPVC or PEX lines. Push-to-connect fittings rated for potable water eliminate the torch or solvent step entirely, seating with hand pressure and a stainless collar. They are what turns this from a plumber's job into a weekend project for most one inch or three quarter inch installations.
Does the filter go before or after the water heater?
Before. Sediment and scale that reach a tank or tankless heat exchanger settle and bake onto surfaces where downstream filtration can never remove them again. Installing the filter on the cold main ahead of the heater protects the heater along with every fixture in the house rather than protecting only the cold side.
Why do I need a bypass valve if I already have a shutoff before and after the housing?
Two shutoffs isolate the filter but leave the house with no water at all while it is isolated. A bypass valve, or three ball valves plumbed around the housing, routes flow around the filter so the household still has unfiltered water during a stuck housing, a cartridge search or a repair, rather than being without water until the filter problem is solved.
What size pipe fittings does a whole house filter need?
Most residential big blue housings ship with one inch or three quarter inch NPT ports; confirm which one before ordering fittings, since a mismatch means a reducing bushing has to be added after the pipe is already cut. Standard 2.5 inch housings commonly use three quarter inch ports and pass considerably less flow.
Is a whole house filter installed on a well different from one on city water?
The mechanical installation is the same, but the location relative to other equipment is not. On a well, the filter goes after the pressure tank so it sees the steady pressure a charged tank provides rather than the sharp swings of the pump cycling. On city water there is no pressure tank to consider, only the main shutoff and the water heater.
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Researched, not professional advice. This page is compiled from published standards, regulatory limits, manufacturer specifications and owner-review consensus, not hands-on testing. Nothing here diagnoses a water problem or says any product makes water safe to drink. Figures described as a rule of thumb are water treatment trade convention rather than published standards, and they are labeled that way wherever they appear. Test your water before you buy equipment: on city water start with the Consumer Confidence Report your utility publishes each year, and on a private well only a certified laboratory test tells you what you have. Bacteria, nitrate, lead, arsenic and PFAS are not do it yourself topics, they are invisible and tasteless, and they need a laboratory and usually a licensed professional rather than a product. Remember that a certification covers a specific claim under a specific standard, so "NSF certified" with no number attached tells you very little.