Just a couple points to figure Watts or Amps.
Volts x Amps = Watts.
1 Horse power equals 746 Watts. So the 1/4 hp is 746 x .25 = 186.5 watts.
KW stands for kilowatt, or 1000 watts.
186.5 divided by 1000 = .18 KW
Then add the load, the pump, the inefficiency and the restriction to flow.
Here's the most important part.
Different pumps have different applications they are best suited for. Ex, in your garage you have an air compressor and a leaf blower. Both move air, but very differently. An air compressor takes a long time to build up enough pressure to fill the tank and be able to blow leaves, and a lot of power.
A leaf blower will never fill you car tire, but moves a lot of air quickly, and less power consumption.
The OP stated one of his primary objectives was "low operating costs".
Keep in mind the goal is to move air, not compress it and waste power.
Let's compare the Gast vs the Hiblow.
According to the charts above, the Gast puts out 4 psi at 4 amps at 3.4 cubic feet per minute.
120 volts x 4 amps = 480 watts.
According the specs below, the Hiblow puts out 4 psi at 100 watts at (100 cubic liters per minute) 3.53 cubic feet per minute.
http://www.hiblow-usa.com/wp-content/uploads/2017/06/HP-100LL-120LL_170308.pdfWhile output to the diffusers is almost the same with both units, the power needed to run the Gast is almost 5 times as costly.
Personally I am running two diffusers strongly at 12 foot depth with 4 psi left on the gauge at the pump with the Hiblow 120LL.
In a similar analogy, if your goal was to leave a light on all the time in the garage. Would you want a 100 watt bulb, or a 480 watt bulb?
