I'm going to basically try to follow what the copper's doing, except there will be more runs down to the basement than there are now. That means I'll have to widen the existing holes a bit.

I will get one of those tubing cutters. For larger sections where there's a bit more room I'll probably use the reciprocating saw just to save time, but for close quarters, the manual cutter will be a lot cleaner and easier.

Regarding the stagnant water thing, isn't the solution to that to just let the water run a bit before drinking, and to use thinner tubing to those fixtures?

You're definitely correct to note that because this is a retro-fit, the sharkbite/push-fit stuff would probably be easier.

The only thing is, they're much more spendy than the clamp/crimp fittings (see this vs. this and this vs. this, for example.) The clamps/crimp rings cost a little bit, but still, it looks like I'll spend at least 4x as much for the push-fit stuff. Maybe the ease of installation is worth it, though...

I have forced air heating, so no need for any of the heating stuff you mentioned.

EDIT: Re: Sharkbites... One downside I can think of is that the perception that they're not as tried-and-true as other connection methods could lead an inspector to say they're unsafe or not up to code. There's a perception that they're fine for temporary connections, but that in-wall connections should be done with crimp rings/clamps. Even if it's not true, the perception could cause me to have problems with the inspector...

EDIT #2: Also, how about the fittings that have to attach to copper? From what I've read, the sharkbite uses a steel ring to grab on to the copper. Isn't there a strong possibility that there's a reaction between the dissimilar metals?

Good idea. Do you have a brand/model of hot water pump that you recommend? I assume the instant availability of hot water makes up for whatever energy they consume?

EDIT: Just did some Googling on the hot water recirculation pumps. It looks like some of them don't even require a line back to the water heater, rather, they just bleed the room temperature (formerly hot) water from the hot water line into the cold water line. Any opinions on which of these options is better? Is one option more energy-efficient than the other?

I don't have one of these, so I can't offer any specific advice. If you decide you want one, then you might as well run a separate "return" line to your faucets, such that your cold-water system doesn't need to mix with your hot-water system. Or, you could just have a giant circle from faucet to faucet, or even a handful of loops -- whatever topology matches up best with your existing house.

My understanding of them is that they effectively use the municipal water as sort of an overflow. Many municipalities now require backflow preventers, which would make that sort of system either impossible or illegal. I don't know about where you live, obviously.

That system would save you money on piping, but I think the other system where hot water is constantly circulating in the pipes makes more sense. Effectively it's just extending your hot water tank almost all the way to the faucet.

Hm, guess I'll go the return-to-tank way, then.

While googling for some more info on PEX, I found this design/install guide (PDF). Wish I'd seen that earlier, since it answers at least half the questions I've asked so far. Oh well. Good reference material, anyway.

I don't think so. They just take from the hot, and give to the cold, canceling out flow-wise. There's no net (or actual) flow in or out of the building with that.

Cheers

Hm. Maybe so. Maybe the extra water being put into the cold water lines will feed back into the hot water tank. Honestly, I'm still a little unclear on how the house's pressure defeats the municipal pressure in any case.

When the water is heated, it expands. If it's a closed system, that means water can be pushed back into the mains. This is a big no-no in UK plumbing regulations, and probably elsewhere too. Traditional UK hot-water systems (and heating circuits) have an open pipe venting into the cold-water tank in the loft for expansion overflow.

Peter

That heated water comes from the cold water line.. so if we're taking water from the hot water heater, it's really coming from the cold line. So circulating back to the cold line just cancels that out.

There may still be a separate code requirement for a backflow preventer, but that's something which is good for garden hoses and even the normal hot water supply as well.

Cheers

My point is that in order to circulate, the pressure at the sink has to be greater than the pressure at the source. If the pressures are equal and the thermostat gate trips, why is the water in the hot water line inclined to move to the cold water line? It seems to me that you'd have to have some sort of motor, and the solutions I've seen along these lines do not have any such thing.

In the US, cold-water tanks are virtually nonexistant. (There are some municipalities where the municipal supply doesn't have enough pressure to put water to the top of their tall apartment buildings, and those buildings will have tanks, but as far as I know, that's pretty uncommon. Other than that New York City is one of them.)

I don't know precisely how US hot water tanks deal with that problem, but I'd bet that there is more space in the tank beyond the point where the tank will shut off incoming cold water.

Looking at our hot water tank, it seems like it's dealt with in the same way as in the UK -- minus the cold water tank. That is, there's an open pipe running down the side of the tank (so that the hot water that vents from the top doesn't spray someone in the face). Any water released in the process will make a puddle on the garage floor.

I'm assuming though, that, like you suggest, there's extra space in the tank to accommodate fluctuations without the need to constantly spill out the pressure release, and the vent pipe is just a safety release.

Ahh.. The ones I know about all have a pump to move the water around.

But the kind with added tubing to return water directly to the heater/tank rely upon gravity induced convection (cold water is heavier) rather than a pump.

A quick update:

I spent some time this weekend measuring out all the runs I'll need and making decisions about which fittings to use, etc.

After much consideration, I've decided that I'm going to give the Sharkbite push-fit connectors a try. While they're much more expensive than the other fittings, the difference is more than made up by the fact that the other connections require specialized tools that cost a minimum of $150 and possibly up to $300. Sure, I can turn around and sell the tool afterwards, but what about when I need to redo a joint or fix a piece of PEX that's leaking? Really, I'd need to keep the tool around just in case, and that pretty much negates the cost savings of the traditional fittings.

Factor in the time that can potentially be saved, and I think I should at least give the Sharkbite fittings a try. If worst comes to worse, I'll return them and go another direction. The ability to join PEX to copper without touching a blow torch or solder really seals the deal here.

The other big change is that, due to some space constraints in my wall where the riser goes to the 2nd floor, I've decided to branch the hot/cold supply lines and send them upstairs to a second manifold, rather than serving them with home runs to the manifold in the basement. This way, I only need to send two 3/4" pipes up to the 2nd floor instead of 10 1/2" pipes. The cost ends up being a wash, basically (save money on tubing, spend it on another manifold) but will save me a lot of install hassle.

I'm just about ready to place my order, and will be taking pictures as I go through the process. The materials list I have right now clocks in a little bit over $1000, but I just found another online store that has the Sharkbite fittings cheaper, so I'll probably squeeze that number down a bit.

http://www.geekstuff4u.com/product_info.php?manufacturers_id=&products_id=836

http://youtube.com/watch?v=XxXx3imY3tM&feature=related

You tube has a load of pex install videos. If I understand it right, you only need, either a crimper or an expander, not both. Crimpers go for $100-150. So the cost of the less expensive fittings will offset the tool cost by a lot. It also seems better to avoid angled fittings if a bend will do. The video above shows one way to avoid in wall right angle fittings.


ProPEX - brand of fittings and tool where the tube is expanded.