"Nicholas Sardo" wrote in message
...
Since there appears to be some confusion on this unit, this post is
meant to clairify:

Aqua Therm is made by First Company, and utilizes a Hot Water Coil fed
from the dwellings hot water heater. This hot water coil is not
"radiant" heat as one respondant hypothicated, but rather incorporated
in a Forced Air Unit. A blower forces air through the hot water coil
and out the supply ducting. A "Taco" pump pumps the water through.
The SAME water that is used for the buildings hot water is used for
space heating. The hot water from the hot water heater is fed through
he coil, and the return feeds back into the cold water supply inlet to
the hot water heater. Obviously there are check valves.

Well, the AquaTherm unit information I gleaned from the web seemed
different. But no matter....

One thing that happens when hot water is circulated might be unexpected.
Nothing happens until you start to seriously draw hot water and then things
change. This situation sounds like that's what's happening.

Example: I had a house with a hot water pump / loop so that hot water would
be more quickly available at the furthest point in the house from the water
heater. We noticed that the water would rather quickly become less than
really hot while taking a shower. If the circulating pump were turned off,
this didn't happen. Why?

The circulating system takes hot water out of the tank as normal and routes
it through the house. The return pipe feeds water into the water heater
cold water inlet side. When there's no hot water being used, this keeps the
water in the pipes hot and doesn't much affect the water heater.
However, when there is hot water being consumed, things change. Instead of
cold water coming in the bottom of the tank and hot water coming out the top
as usual, hot water mixes with cold water coming into the bottom of the
tank. This causes more mixing inside the water tank than normal and quickly
enough the entire tank goes to a lower temperature. This is in contrast to
the normal situation where there being a rather sharp temperature gradient
between cold water at the bottom and hot water at the top.
So, this can be annoying.

There are a couple of solutions:
One can attach a hot water heater thermostat to the water heater inlet pipe
that controls the circulating pump. The idea is to stop circulating if the
inlet water is cold. Something like that....

Another approach is to put two hot water heaters in series and only
circulate water from the heater on the outlet side of the pair. This way,
there's no cold water mixing in the outlet side heater until the inlet side
heater runs out of hot water. The outlet side heater can be small because
it's only other purpose is to circulate hot water - which shouldn't take
much energy if the pipes are insulated. The inlet side heater is not
subject to the kind of mixing that occurs with one heater plus a circulation
pump.

Now, if the energy loss in circulation goes up then the outlet side heater
would need to be larger and this wouldn't be such a good solution because
mixing would occur. However, it's probably better than not having two tanks
because really cold water isn't brought into this "mixing tank" right away.

Fred