How do I test fuel efficiency of generator?

here's another SWAG. 13,000BTU AC. Let's assume draw is about 12A and PF=1, so 12Ax120V = about 1500W load. 1500W=5000BTU (IIR 1W=3.3BTU). Let's assume the generator inverter is near 100% efficient (which they are close to, at least for this excercise) OK, most internal combustions engines run about 20% thermal efficiency. so to get 5,000BTU/hr output= 25,000BTU/hr input. Propane is about 80KBTU/gallon, so figure 1/3 gallon of propane/hr.

Note: do NOT use the AC output BTU, and it doesn't violate any physics that AC output BTU is greater than the input BTU. An AC MOVES heat from inside to outside it doesn't create heat, except for the energy needed to overcome the losses in the heat transfer (compressing the gas and letting it then boil to remove heat)

Forest Camp.

Lbs of fuel per kWh is the industry standard for determining efficiency. If you maintain temperature so as to force the A/C to operate 100% of the test it is a valid test. Also, do the same test, same duration 0% generator loading. This will give you some perspective in case you are curious.

I like the scale idea. I'll probably go with that.

Let's see if this guess is about right...

4-6 hours per pot, for 100% A/C run time. Time (later on) will prove me right or wrong...

Some owner's manual will list the fuel consumption at different loads. My Onan manual for my 2.5KW propane shows half load, quarter load, etc. for planning I use the half load figure of 1.5 lbs of propane per hour. Since propane weighs about 4.5 lbs per gallon, I expect to get about 3 hours per gallon, running my AC. Without the AC, it will be closer to the quarter load figure.

The figures for your generator should be available in your manual or on line at the Generac site. Otherwise, as mentioned above, weigh your tank before and after running for an hour.

smkettner wrote:
Remove the tanks before and after the test and weigh them.

Simpler still:

Stick a bathroom scale under the operational tank, read the weight, run the A/C for a few hours, and read again.

FYI, if it helps:

There are 21,548 BTU's in one pound of propane.
(Since it actually changes volume according to temperature, weight is really the only way to get a real reading of how much propane is used.)

Remove the tanks before and after the test and weigh them.