Yes, the heated towel racks that I have made, were all 3/4 inch copper pipe.
Basically four pipes of ~9 inches long fitted together with 'T's, standing vertical, the top is not a 'T' but a 90 degree elbow with the air-bleed fitting.
Four rungs of whatever length. One at ~ 1 foot high, a second ~2 foot high, a third ~3 foot high, and the top rung at ~4 foot high.
And the other end piece: of four pipes of ~9 inches long fitted together with 'T's, standing vertical, the top is not a 'T' but a 90 degree elbow with the air-bleed fitting.
Our towel racks not only heat and dry towels, but they make the greatest air separator units. All air that gets into the system will collect in that top rung.
I did mine with copper, MAP gas, that brush-on flux that self tins, and solder.
That tinning flux has got to be the greatest invention of the century for handling copper pipe.
The only problem that we have experienced, is that it looks ugly. I tried painting them with silver rustoleum paint. and my wife hates their look. Though she would never trade them away, she likes having heated towel racks. But we have to think of a way to make them look better.
Our are in the city, so it power goes down everyone in the city goes without heat. So I do not feel so bad for the renters, as a loss of heat would not be isolated to just their apartments, but the entire city.
Now for our homestead, I want our pumps to be 12Volt DC.
If you are doing this for your home, I would recommend that you use 12 volt DC pumps. So if you do lose power, you can still circulate the water.
Does TACO offer pumps in 12volt? Right now, I am still installing windows and insulating, I will not really be working on the water parts for another week.