Hi, I live in Long Island, NY. My current heating system is a 50+ year
old American Standard boiler with a Beckett oil-fired burner. Attached
to it is an uninsulated indirect water heater of unknown brand (which
is probably as old as the boiler). Most of the system is as old as the
house, which was built in the early 50s (the burner and a couple of the
circulators are fairly new).

For some reason, the previous homeowner (who was also the homebuilder)
connected the indirect water heater to the hot water coil of the
boiler, rather than using the recirculated boiler water. The system had
been working fairly well, although I suspect not at top efficiency (we
had insulated the water heater using a fiberglass water heater blanket,
but there was still some heat leakage out the top).

Anyway, recently, we've been having problems with the boiler pressure
triggering the pressure relief valve. After I empty the expansion tank,
the pressure gauge goes down to a more reasonable level; a couple of
weeks later and the pressure is high again. Our serviceman came out and
told us that there is a crack in the hot water coil (I'm not sure how
he concluded this, as I wasn't home at the time, and I didn't think to
ask). Now, since indirect water heaters don't require a hot water coil
(and when I tried to run our domestic HW directly through the coil, the
pressure was awful), I'm thinking I can just plug the HWC and attach
the water heater directly to the boiler. Now the questions ensue:

1. Is the conclusion about the cracked hot water coil valid? Is there
anything else that might cause this situation (boiler temperature is
being regulated properly at 160F)?

2. I'm thinking that since I'm doing some major work on the system, I
might as well replace the indirect water heater at the same time (I
don't want to get involved in replacing the boiler; I know it's not the
most efficient but that would incur enormous expense which would
probably not be recovered for a couple of decades; the sytem has been
fairly reliable except for this issue). I've noticed there are two
major types: most have a large recirculated-water tank with a coil for
domestic water; however, Phase III (and possibly other) heaters have an
outer and inner tank (this is how I had assumed they were all
constructed before I started doing research). Is there any advantage of
one over the other? The Phase III heaters have a much larger domestic
tank than recirculated-water tank.

3. The installation instructions for the Phase III heater explicitly
specify not to plug the old hot water coil (their exact words:
"Plugging tankless coil inlet and outlet will [sic] result in severe
personal injury, death, or substantial property damage."). Now first,
it seems to me that if the coil is completely purged of water, the only
thing in it will be air, and expanding air won't be enough to rupture
the coil. Additionally, I've seen similar systems in other homes where
the HWC HAD been plugged; also, since our coil is already cracked,
additional damage will be minimal or non-existent. Thoughts?

4. The house is a two-family home; figure average occupancy is 6 people
(adults+children). Any way I can easily calculate the size heater I
need?

Post responses to the groups, please; this email address is now owned
by the spammers.

Thanks,

Steve