As you can tell, the answer is not just a simple 'get this'
each response so far has merit and holds part of the answers.
There is a unwitten rule that the quality of the anwer is directly proportional to the quality of the questins.
now, we have to make some wild assumtions here.
as WVMARLE said, get a gallon tank, get it hot, and just use that to circulate.
since we do not know your actual use, that might work great.
in a distillation column, you get the jacket up to some temperature, you said 160.
if you want, get an old coffee maker, use the heater and relay and circulate the fluid through that. it might take 5-10 minutes to get it up to temperature, but since we do not have a great grasp on what you need, it may or may not work.
It would seem to me that you have two conditions, start from cold,and a keep warm.
staring from cold would require a lot of heat. keeping warm, not so much. more of a nudge to add a bit more heat......
the best answer lies with better details. if you are doing a still, and heating vapors to your temp, then you only need to 'keep it warm'
if you are heating ground water to 160 for washing hands or dishes, (more like 2nd degree burns on hands, and sterilizing dishes) your process has a MUCH higher energy requirement for heating.
I would recommend a water temp in and water temp out of the column, give you an idea of the heat transfer in the unit.
A small, and I mean tiny/small coffee maker pump can be had from Amazon or E-bay and it can be controlled with a a relay or variable speed.
as you will learn, high volume water flow = high transfer rates
low volume, high temperature = high transfer rates.
good surface conductor materials = good heat transfer rates
your answer may lie in a combination of things.
as for the '1 gallon' is that your total storage for circulation ? wherein your storage is 160 and the returning water temp is 155 ?
or is that 1 gallon per minute from 45 degrees starting temperature ?