Help using thermistor with esp8266
Considerations about the ESP8266 analog pin

The ESP8266 has only one pin that allows analog read. This pin is call A0 on the NodeMCU module or A on the ESP8266 Huzzah (some other ESP module don't expose that pad - for example ESP8266-01) or might label it differently - check the documentation of your ESP module.
Following your edit: make sure that you connect your thermistor to the A pin of the Huzzah ESP8266 module.

You should keep in mind that this analog pin is a 10bit ADC with in principle limited input voltage range.

To read an external voltage applied to the ADC pin, use analogRead(A0). Unless you are using a board specially design to increase its range, the input voltage range is 0 — 1.0V. As @dandavis pointed out some boards (Node MCU e.g.) include a voltage divider on board to give you a full 0 - 3.3V input range.

Thermistor equations

The datasheet of your thermistor states that the TCR coefficient is 3000ppm/%C and has a 10K value [note that the manufacturer doesn't provide you with the temperature at which R = 10K]. The equation of the resistance variation ∆R with temperature variation ∆T is given by:

∆R = ∆T*10k*3000ppm = 30*∆T

So if T_0 is the temperature where R = 10k, the equation of the resistance value is given by:

R = 10k + (T-T_0)*30

I am assuming that you are using the 3.3V supply of your ESP and creating a voltage divider using the 1K resistor and the thermistor.
There are two ways to do this divider:

1. Voltage divider option 1







simulate this circuit &ndash; Schematic created using CircuitLab

[Note that the thermistor needs to be connected to the A pin of your ESP8266.]

2. Voltage divider option 2







simulate this circuit

Equation of voltage at node A

For both case here is the voltage V_A seen at node A:

1. Voltage divider option 1

V_A = R_series *3.3 / (R_th + R_series)

2. Voltage divider option 2

V_A = R_th *3.3 / (R_th + R_series)

Analysis of the variations of V_A with temperature

Lets look at the difference between the 2 formulas above:

1. Voltage divider option 1

The numerator is a constant with temperature while the denominator changes with T. You will get a strong variation.

2. Voltage divider option 2

Both the numerator and denominator increase with temperature. You won't get a lot of variation on V_A with temperature. You should avoid this configuration.

Analysis of the maximum allowed value of R_series

The important consideration is that for your ESP module V_A cannot be higher than 1V.

1. Voltage divider option 1

Increasing R_series will increase V_A so we compute a maximum value:
1V = 3.3V*R_series_max/(R_series_max+10K)

That gives you: R_series_max = 4300Ohms

2. Voltage divider option 2

Increasing R_series will decrease V_A so we compute a minimum value:
1V = 3.3V*10k/(R_series_min+10K)

That gives you: R_series_min = 23kOhms

This is the reason why it was suggested to you using a 30k resistor in that case.

Considerations about temperature measurement precision

The voltage variation ∆V on the node A of the ESP between temperature T1 and T2 can be computed as follow:
∆V = 3.3 *1K/(1k + 10k + 30*T1) - 3.3 *1K/(1k +10k+ 30*T2)

If we assume that the thermistor is 10K for ambient temperatures the baseline voltage measured on the A pin is:
3.3V*1K/11k = 0.3V

For a 0 to 1V 10bit DAC of the ESP8266 that is around: 2^10*0.3 = 307

A change of 10C would lead to a variation of voltage of:
∆V = 0.3 - 3.3 *1K/(11k + 300) = 8mV ~8ADC code

The equation of ∆T vs ∆V is not linear but for small variation of temperature with your current setup you get ~1ADC code per degree.

Depending of your application this might not be enough for you. As suggested in several comment you could:


Add more thermistors in parallel
Increase the 1K series resistor (but not too much or you will saturate the ADC).
Change the architecture of the measuring circuit (RC oscillator using the thermistor and interrupt counter in the ESP, 555 timer circuit loaded with the thermistor and interrupt counter, ...) 
Or since you want to do humidity and temperature measurement why don't you get the BME280 module. It can be read over I2C and libraries are readily available to read it with the ESP8266.