(I’m assuming you’re in USA)

The other commenters have correctly described how you could run metallic conduit (EMT) or PVC, and that would be perfectly acceptable for “low voltage” wires like twisted pair Ethernet. But it’s also kinda overbuilding it, because EMT or PVC are also suitable for “line voltage” AC electricity. Other conduit types are available, depending on your jurisdiction, since EMT is meant to provide physical protection and PVC is meant for be water-resistant. And both provide physical support for the wires within. None of these qualities are really required for Cat 5/6 cabling.

Here in California, it is permissible to use ENT – with an N – also known as Smurf tube for its blue color, for line-voltage applications where no environmental protection (physical, UV, vibrations) is required. Smurf tube is made from thin, corrugated plastic in standard sizes, so it’s easy to pass through top-plates and anchor to studs. This makes it an excellent choice for organizing low-voltage wires, or for future proofing.

Indeed, if you really wanted to, you could terminate the Smurf tube into standard outlet boxes, so that there’s zero exposure to the insulation batts within the wall, for when you later fish the cables through. For a still-acceptable arrangement, the Smurf tube could be anchored just above where you’ve cut out a hole for the future wall-plate, allowing retrieval of the cable through that hole. You should not later use these conduits for AC electricity though, and mixing low-voltage and line-voltage in the same conduit or box is typically prohibited.

I do think that conduit is true future proofing. Who knows if CAT6, 7, or 8 just gets replaced (finally) with fibre optic cables. Or perhaps you decide to become a ham radio operator and thus need to run specialized coax. Or maybe you really want a 50 ft HDMI cable from the upstairs living room down to the man-cave in this basement. Running wire today is temporary, but conduit is forever haha.

You can do this with PVC pipe and some glue and straps. Once you put the glue on and put the two pieces together, hold them tight together for a few seconds to let the glue set and prevent them from sliding apart a little bit. Your local code might dictate how far apart the straps should be, but generally you put a strap close to each end, and then spaced the same as your stud spaces along the length of the run. As for the size of the PVC that depends on your future needs… I would guess 1" or 1 1/4" would be more than enough? You can use a fishtape to pull your ethernet cables through. When you do this also pull through a string so that if you want to add cables in the future you can just use the string to pull them through. Always remember to pull a new string through for future you as its harder to get a fishtape a pipe with stuff already in it

You might find smurf tube easier to run and it’s perfectly cromulent to pull cables through.

When our house was being built, we had them install a pipe chase from the basement near the fuse box to the attic, specifically for me to be able to run whatever cable I wanted to later on. This was done with 3" PVC (I think, I haven’t looked for a while).

I’m seeing other people suggesting much narrower conduit, and I would have to advise against that. Let’s say you already have a couple of ethernet cables run through your pipe chase, and you want to run another one. Having plenty more room for the fish tape with the new cable attached is going to make it much easier to pull that new cable through.

I would run the largest conduit you can fit.

When I do runs i do at least 3 lines in case one fails. In my garage I just setup an old router as a wireless bridge with open wrt.

Check your local building code, conduit is probably not needed

I would keep it simple and get 1/2" metallic EMT conduit. Unless you’re running multiple lengths of cat 8.2 ethernet cable through–and you might want to do that, IDK–you shouldn’t need larger.

You’ll need a bender, a hacksaw and/or cordless band saw (something like this), something to deburr the inside and outside of the conduit after you cut it, and you’ll need a hole saw large enough to run the conduit through (for putting holes in studs). You can use stud shoes if you end up needing to reinforce the studs because the hole is large. If you’re running through joists, check building code in your area on where they’re supposed to go. The strongest location is at the top of a joist, at the bottom of the joist will weaken the joist, and your local building code may require middle.

If I were you, I would suggest not putting more than 360 degrees of bend in any run without also putting in a junction box that you can access once the drywall is installed (this is probably also a building code issue). The more bends you have in a run, the more difficult it is to get your fish tape through the conduit. Unless you don’t have any other options, I would not use the elbow fittings except where they will be exposed; you won’t be able to push a fish tape through/past them. The tighter the bend in the conduit is, the harder it’s going to be to fish wires/cables through.

Oh, and you probably shouldn’t use the same conduit for electrical runs.

Hope that helps.

For how much, I would do one per room as minimum, and one per wall as maximum.

I have not seen it mentioned, but get the fire rated stuff. No good to have the rare fire spread through cables.

If you are able to terminate Ethernet yourself or plan on being able to in the future (the hardest part is probably buying the crimping tool), you could just buy a spool of Ethernet and run it now. Either leave the ends loose, or you could terminate them into female jacks in wall plates (just find a good way to label them for your future self).

Depending on your budget, Cat5e would probably be fine, but if you want future proofing you could do Cat6. Technically you can go higher but that’s probably more than you’ll ever need.

Conduit can also work, but you need to make sure you’re able to fish wires through. Could be useful to think about how you’re going to do that, and it kind of depends on the setup. Some way of leaving a string, or perhaps fixing a string into a loop so you can use it as a pulley to pull things through. If it’s a short, straight shot that might not be necessary.