Idea of getting extra efficiency out of electric heater was on our minds for quite a while.
After taking some copper tubing out of commission a small model was soldered together for a test run.

Copper frame filled with water sitting at an angle and lower part is placed by the air vent of electric base-board heater.


Water in a frame gets hot and natural circulation starts bringing hottest water to the top of the frame and once it cools down it goes around to the bottom part.

This is how the test frame looked before being cleaned-up:





and this is after:





Result:
Pipes got real hot when heater is on and keep prettu good temperature after it shuts-off.
As seen on a temperature graph - heater turns-on less and temperature stays warm longer after heater turns-off (Lime line for Bathroom).



Next - the same heater for a living room with ribs on the top portion.

Also, special brackets were 3D printed to keep the heater in-place:




Total expense:
Copper pipes: $0
Copper elbows: 3 x $0.98 + 3 x $1.40 = $7.14There's no place like ~

STL file for the bracket:
www.codemacs.com/download..There's no place like ~