Derek Campbell said:
My brother in law replaced a copper coil (with several patches) with 3/4" copper pipe making several loops around the tank (square, home made) and it seems to work fine. I don't remember the size of the tank or length of coils / piping.
I was always curious about using baseboard piping with the aluminum fins. Should increase heat transfer and reduce the length required.
Does anyone have any simple formulas to calculate the heat transfer of tubing etc in a tank so one could get a reasonably accurate estimate on the amount of tubing required?
Goose said it right, aluminum fin tube will not work very well and the fins would eventually corrode and plug anyway.
There are enough folks here who have done fine jobs with smooth copper and PEX hx. You do need to pay for the surface area of either material to get a decent hx, but this is the most economical way to go.
Plate hx are certainly a different way to go, with many people getting excellent performance. Of course, you trade off an extra pump against a slightly more passive design.
One final way to look at this is to consider using the tank water directly into a heat load. This works fine with radiant floors on a house that is on a single floor.
I am heating my home via a tank, with only a DHW hx. We pump tank water via a bronze 007 to the radiant floor and walls. I did replace a steel radiant panel
with a double layer of fin tube baseboard that I built into a custom tall case. The taller the case, the better it works with low temp water.
The house stays at 70-72F with 105F water. Yes, it is superinsulated, but that only lets me get away with lower temp water.
The unpressurized system would work with most systems if you remove all the iron/steel or thoroughly treat the water.
We have done both. And we are heating two levels.
We do have a 25 year old system at the University of Maine that operates this way with iron pumps and corrosion inhibited water.
Only the DHW hx and we pump tank water to two levels.