HJL,
The difference between CNG and piped-in gas to your home is simply pressure. The gas in my house is at 7 psi and if your thumb is big enough you can stop the flow. CNG could be as high as 3000 psi, and you find it in tanks for vehicles that burn natural gas and filling stations for natural gas burning vehicles. The difference between butane, propane, and natural gas is British Thermal Units (btu) generated by a cubic foot of each substance. From high school, a btu is the amount of energy it takes to raise one pound of water one degree Farenheit at one atmosphere of pressure. I know that propane generates 20% more heat when comparing the same quantity of that to natural gas. I’m not sure where butane falls in there. The difference in heat yield is dealt with by changing the orifice through which the substance travels to be burned. It is very dangerous to change gases and not change orifices. Butane always comes in a device with a tiny opening. I would infer that its yield is even higher than propane. You find it employed in handy small devices all the time. I have a kit to install on one of my generators that claims to allow use of propane, natural gas, or gasoline. It relies on a needle valve to adjust the flow of fuel rather than an orifice change. The kit is in a box because I am waiting on some free time to install it. Guess you know how that is working out. There is also equipment that involves a venturi valve that will dilute propane with air as it flows from the tank to the device burning it so that the btu yield is reduced to that of natural gas. This equipment has industrial and institutional applications and is priced accordingly. Another nuance on gases is that natural gas floats. It is lighter than air. Propane on the other hand is a product of the crude oil distillation process and is heavier than air. It will collect in a low spot and potentially explode. As a consequence, you have to be careful about installing propane equipment over basements and crawl spaces. Certainly it is done, but you cannot have a switch that sparks or a device with an igniter in your crawl space. You just have to be conscious and careful. It is universally held as a bad idea to install propane-fueled equipment in a pit under your house. I dug that pit when I was young. Fortunately I learned the “propane collects” lesson from advice and not launching my house. RV