Sealed Pressuried Advantages:
1. Easy to refill, reduced airlocks
2. No pumping over.
3. Limited discharge of water in the event of a leak.
4. Easier to set up
5. Required for modern boilers.
6. Cheaper to install.
7. No tanks in loft.
1. Automatic topup (opposite to (3) above)
2. Required for ancient boilers
I don't know if US systems are different. In the UK, it is typical to plumb
a sealed pressurised primary to be manually refilled. This means that the
total loss of water is limited to the capacity of the system. I'd hate to
come back from holiday and find a weeks worth of water has been pumped into
the house via a leaking radiator valve.
It also means you get to know about leaks sooner rather than later because
the system pressure drops. Automatic top-up might conceal that fact that you
have a leak.
Most everybody in the US is putting in PRV's to automatically feed boilers.
Many old-timers prefer to manually feed the boilers for the reasons you
give. I also think a manually fed system ( for hot water, not steam
boilers) is the best way but like everything else, the customers want
everything automatic and they don't want to learn to go down and look at the
gauge on the boiler once in a while. They want everything to work
perfectly forever with no maintenance at all.
No maintenance except cleaning up the nasty sludge from their systems which
have been slowly leaking and adding new oxygen and scale over the years,
whilst diluting the corrosion inhibitor. Still, that sort of maintenance is
to be done by the heating engineer for loadsa money. ;-)
Out of interest, what is a typical plumbing setup in the U.S.?
A typical newly installed British system would be:
1. Natural gas hot water boiler with modulating burner (possibly condensing)
2. Internal pump with overrun.
3. Sealed pressurised primary circuit. Manual refill.
4. Separate zones for hot water cylinder and central heating radiators.
5. 2 channel programmer to determine timing for zones.
6. Room thermostat to control heating zone.
7. Thermostatic radiator valves in other rooms.
8. Radiators run on two pipe in parallel, across flow and return lines.
9. Unvented hot water cylinder off a 3bar (~40psi) PRV.
10. Electric backup heating element in cylinder. Rarely used.
11. Hot water zone controlled by tank thermostat.
12. Automatic bypass valve between unzoned flow and return.
On smaller houses and flat (apartments), a "combi" boiler would be normal.
This cuts out the zone valves and hot water cylinder. Instead, internally to
the boiler, the entire boiler output goes through a plate heat exchanger
connected to the incoming mains (or 3bar PRV) which is heated
instantaneously when required by a flow switch.
On larger houses, or more sophisticated systems, the heating may be
subdivided into more zones, such as upstairs and downstairs, or room by
room, with different timings and temperatures for each zone.
So, do these systems differ markedly from U.S. practice?
on average your heating systems are much more modern in the U.K. then
we have over here, mostly due to energy conservation which is your #1
goal. Yes, we have all the bells and whistles available to us but only
a small percentage of our systems will include any. On average most of
our residentual heating consists of the old fashion series loop,
mono-flo, one pipe, two pipe or two pipe reverse systems. We zone with
zone valves or circulators. We usually keep our systems very simple
and in turn they are cost effective by our standards.
We do occasionally get the chance to be creative and go to town with
the new stuff. Here is a link that might be of interest to you:
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