On a recent segment of This Old House (the one they’re spec’ing), they showed dual supply lines for both the cold & hot water to all the fixtures. While pressure surges might be eliminated (that’s what they claim), I don’t see how it’s going to improve the hot water flow to the fixtures. Assuming the hot water lines (both legs) are allowed to cool to room temperature. Now, if the fixture adjacent to the water heater is turned on, that shorter leg’s hot water temperature will be tempered by the action of water coming in from the longer leg. Not until both legs are filled with hot water will the temperature at the fixture reach the water heater’s temperature setting. (Of course, I’m assuming negligible heat loss.)
Anybody have any comments?
Butch
Replies
You mean four lines total? Makes absolutely no sense -- could just run a larger-diameter single line.
Yes. There were two complete circuits running completely around the house and the various fixtures were T'd into those two lines. Where there were several fixtures adjacent to each other, a manifold was connected to the hot and another manifold connected to the cold. From each manifold the branch lines lead to the fixtures.
butch
So it's a circular system, kinda like the way they wire outlet circuits in the UK. The water can be drawn from either direction, depending on which direction has the least resistance, and whether some other fixture is drawing water somewhere else in the "circuit".There's probably some conceptual merit to this, but only if the layout is conducive to a circular arrangement -- coercing the piping into a "circle" when it's really spread out differently would seem to cause problems.I think there are generally better ways to deal with the usual pressure problems.
While this system will solve the pressure drop/surge problem, in the hot water circuit; however, the difference in water volume between the "legs" from the heater to the fixture will cause differing water temperature to be supplied to the fixture. This temperature difference will continue until the longer "leg" has been purged of the lower temperature water.
I just don't think it would work for the hot water circuit.
butch
I would agree that the range of applications for this scheme is fairly limited.
Since this is TOH's spec house, I'm assuming they're hanging on all the bells and whistles.
butch
On the other hand, with the hot water supply already configured as a ring, it would be easy to install a circulation pump and keep the water hot all the time throughout the ring.
The show didn't indicate that that's what they were doing.
With the size of the house, I would think it would be cheaper to install tankless heaters located nearer the locations where the hot water would be needed.
butch
Yeah, if I had my druthers, and an infinite budget/utility space, I'd install local tank/tankless heaters in all of the baths, combined with a pressure reducer system to assure uniform pressure.
On the other hand, with the hot water supply already configured as a ring, it would be easy to install a circulation pump and keep the water hot all the time throughout the ring.
I think thats the idea - Instant hot water.You get out of life what you put into it......minus taxes.
Marv
In one series, the Napa Valley house (I think), they used a circulation pump to keep the hot water available in the lines.
I installed an electric tankless heater beneath my kitchen and it takes only a few seconds to get steaming hot water from the line (about 1 quart - measured it).
I also emailed TOH but I don't expect a reply. I only received their standard reply.
butch
I didn't see that one, but it sure doesn't make a lot of sense to me. I would need more info before I would buy into that one. - lol
Didn't make sense to me either, that's why I posted my comment on BT. Sounds good in theory but in practically it looked too far out.
BTW, I posted a message on the TOH site and asked for a further explanation.
butch
Butch are you talking about a manifold system?
The info I got was to install 3/8' pex to all the lowflow fixtures that don't flow over 2.5 gpm and are not over 80' from the fixture
1/2' to everything else except the whirlpool which would be 3/4'
This info was from the Zurn company in there pex manual.
There rep told me that in there test it took 22 seconds for hot water to reach the fixture with 1/2' pex vs 7 seconds with the 3/8' pex
All the info that I have found about manifold system state that there is normally a 1-2 psi pressure loss thru the system when multiple fixtures are running at the same time.
This info is fine in a test lab but I haven't really heard any in the field results yet.I also don't know how this system works on well water and pressure tanks.
Greg
Lead,Follow,or Get the Hell Out of the Way!
In that one show, the main lines were 3/4" connected to both ends of the manifold and the branches appeared to be 1/2". All the manifolds were connect to the 3/4" circuit.
butch
All they claimed was that it would eliminate surges. They never made any mention about delivering hot water faster.
I just watched that episode.
I know that's what they said; however, I'm raising the question of hot water delivery. After all, in large houses where the source is far from the point of use, waiting for hot water to come out of the faucet is a big problem to me. Especially, when you consider the lifetime of the system.
butch