Sensing concentration of methane with MQ-4 methane sensor? I'm on a project to sense any amounts of methane in the home. I have bought the popular MQ-4 methane sensor from SparkFun: https://www.sparkfun.com/products/9404

I've looked online for any sample code, but I am confused as to whether the input from the sensor is already given in parts per million, or it is just a voltage. To be specific, here is the sample code the data sheet for the sensor gives: 

int sensorValue;

void setup()
{
  Serial.begin(9600);      // sets the serial port to 9600
}

void loop()
{
  sensorValue = analogRead(0);       // read analog input pin 0
  Serial.println(sensorValue, DEC);  // prints the value read
  delay(100);                        // wait 100ms for next reading
}


I have also used a breakout board for these sensors: https://www.pololu.com/product/1479
The sensor is soldered on it, along with a 20K ohm load resistor, like how the spec. sheet specifies. 
However, I am confused on the readings I am getting. It's always something that ranges between 259 and 261. Is this ppm of methane in my home? If it is, shouldn't the normal level be 0? I currently have no methane based heating. Or is the 259 - 261 voltage?

Thanks for any help.
Actually, you are getting raw data from the sensor. A little bit of math should be done in order to calibrate it and based on the chart in datasheet, measure the real value in PPM.

The calibration basically helps you find R0, which is an internal resistance (along with RS form a voltage divider) that could be derived by doing calibration in a clean environment. After that, you use R0 to calculate a ratio and then look at the datasheet's chart to measure whatever gas you want since there is a curve describing it.

Please refer to this tutorial for more information. I have developed a similar application using MQ-4 before.

It is related to MQ-2, you may have noticed that all theses sensors have similar features and principle applications.