Two years ago I put specialized Central Vac PVC pipe into the walls, under serious time constraints, right before we put up drywall. I had no idea what I was doing, but it only cost about $100 for all of tubing and fittings, about half of which stayed in a box down stairs, unused.
Note: Vacuum tubing is different from plumbing tubing. They aren't interchangeable. In any case, even with a number of screw-ups, it was pretty easy diy (given a bit of head scratching).
Note that you'll also need to run low voltage wire with the vacuum tubing. This is what actually trips the signal back to the vacuum to turn on when you insert the tubing into the wall.
You'll want to tape the wire to the tubing to keep it where it belongs and away from drywall screws, or anything else that can snag, stab, cut, etc. Recommended is that you tape the wire to the backside of the tubing, away from the drywall, in case some time down the road you decide to hang a picture or attach a 2x4 right in front of the wiring.
For the low voltage wiring, you want to create one big loop circuit that can be closed by touching the 2 wires together and closing the circuit. (This means one big loop going around to each vacuum inlet, leaving enough wire at each inlet location to wire the cover when it comes to that. Be generous.
Eventually you'll need to attach the wires to the back of the cover plate and snip off the excess.
When planning out the tubing, you want to try to run the tubing with minimal bends. The less bends, the less likely something will get caught in there.
You'll also want to plan out the locations of the inlets so that you can readily reach every corner of the house with a 30' hose.
We dry fit the entire assembly together before we used the PVC cement to connect the fittings together. If a fitting is easy to access, but also not likely to be disturbed, cement is unnecessary.
I'd say the toughest part for me was not knowing exactly how to terminate the tubing at the wall inlet locations before the drywall went up, so when it came to that, I just left the tubing so it would extend past the drywall a few inches. (Better to have too much sticking out than not enough).
I ran a 90-degree or "Y" sweep fitting from the vertical main line (going up through the house from the basement) to where I wanted the inlet on the interior wall. We put the inlets about 18" up from the floor, but realistically, you can put them anywhere you want, even in a ceiling.
If you keep the front edge of the 90-degree sweep fitting about 1" from where the drywall will be, you'll be glad you did. I dry-fit a short length of PVC to the main pipe and let the drywaller do his thing around it. Later on, you can easily remove the PVC and fit almost any inlet type to the pipe with a few cuts and connectors. The reason that extra 1" is important can be seen below. Note that the inlet fitting and connective PVC is rather protrusive. You'll want the extra room.
The result, as you can see, is an inlet that sits almost 1" from the wall. Not acceptable. Now, we could put a piece of trim behind the inlet, but it still would look lame, albeit a more finished kind of lame. So, what to do? My solution was to fabricate a shallower fitting that will allow the inlet to mount closer to the wall.
I found a reducer that would fit snugly to the inlet, but which would easily fit inside the PVC elbow. I then glued a small ring of PVC on top of that fitting, essentially making a collar that will allow the inlet to tightly fit inside the PVC elbow.
After getting the CV PVC tubing squared away, and all the inlets in place and anchored, it was time to install the vacuum unit. Step one, find an appropriate place to mount the unit. I decided that it wouldn't be worth the effort to try to mount a bracket to the weeping stone foundation, if it was even possible. So, I decided to suspend it from the floor joists. Of course, I had to scrape any spray foam insulation off of them.
Then, I screwed two 30" 2x4's to two joists perfectly plumb. Then, to those, I screwed a hefty piece of 1"x 14" pine. Plywood would have been fine, too. Then I measured from the attachment point on the vacuum to the top of the unit. I then added a couple inches to that and then used that as the minimum distance from the joists that I could screw the mounting bracket.
Now, we got an Air-Way system built for a 8000 sq' home (almost 4x more than needed--OVERKILL!!). The motor is huge so it has to work less hard and thus will (theoretically) last forever. You can vent these units outside, too, to really cut down on allergens in the house. Unlike a regular vac, you aren't blowing dust around the room as you vacuum. Dust goes in, but air isn't exhausted into the room. We hung this unit from the mounting bracket.
Here you can see the unit hanging in front of the mount I created from the 2x4's hung from the above joists. It hangs on the board like a picture frame. It's not very heavy at all.
After hanging it, it's just a matter of wiring the low voltage to the vacuum and attaching the CV PVC to the unit. Remember, that wires go to each inlet and when the hose is connected, it allows you to turn the unit in the basement on or off from the vacuum hose handle.
BTW: When you run the last run of PVC to the vacuum unit, it is not really necessary to cement the PVC together. In fact, if there is a blockage or a need to move the unit, it's just a matter of detaching either clearing the pipes or adding whatever is necessary. Almost all the tubing in the basement is dry fit together.
The final step is to either run the vent outside, or put a muffler on it for sound dampening.
It's a pretty easy install and a HUGE improvement. There is no comparison to a standard vacuum unit.
Even for a retro fit, I'm thinking this makes sense. Basically, if you can get tubing up and around to enough locations so that your 30' hose will reach all the corners, it's a go. You can mount outlets on or in walls, in or on cabinets, floor trim, or the floor itself.
Kitchen installation and first floor is usually pretty easy. As you go up, it's trickier, but you can even run the tubing up the cold air return. You can also cut the wall in a closet if you have to in order to run tubing and low-voltage wire.
Addendum from DW:
OK, here's the cost breakdown:
Our vacuum unit ~$500
The kitchen 'magic dustpan' $40*
The wand and the beater brush unit, stair tool and accessories cost: $270
And the most surprising part of all... the vacuum hose was about $225.
"WHAT? The hose is $225??" sayeth the Wife with the look of total "WTF" on her face to the poor salesman (who was not so poor after we left.... ahem.)
Yes. The HOSE has electrical wires spiral ling all the way down the 30' length, from end hose connector that goes to the beater brush and wand (This is the electrical connection that comes from the wall that makes the brush spin. Otherwise, all you get is a sucking hose) to the wall where the wires, once you plug in the hose to make the connection, turn on the unit in the basement.
So if you are planning on getting a CV unit, plan on the hose and the brush & wand stuff being about half of the cost of the setup.
*magic dustpan. This almost requires a demonstration. Chance for the wife to make a video. :-)