Programming arduino nano via esp8266

Is there a way to upload sketches to arduino nano via the esp8266 after I have the later connected to my wifi router?

No.

But what you can do is stop using the Nano and (I assume, you did not say) the esp-01 module, and replace them with an esp-based board such as a Wemos D1 mini. These can be re-programmed "Over-The-Air" (OTA) and you will have made your project simpler over-all.

Thank you very much! Would I be able to connect an NTC thermistor on Wemos D1 mini and program Wemos to read temperatures (It looks like I could) ? This is what I have successfully done with my arduino nano and am able to use it as a P.I.D. controller => SSR .

I am looking for ways to be able to change those set parameters via wifi.

it is possible to upload to Nano over esp8266. there are even two or three options for ISP or Serial over bootloader, but it is much simpler to use only the esp8266 dev board.

superJj:
Would I be able to connect an NTC thermistor on Wemos D1 mini and program Wemos to read temperatures

I am looking for ways to be able to change those set parameters via wifi.

Yes, you can, but only one thermistor, because all esp8266 have only one analog pin. If you need more analog pins, you can add more using external modules like ads1115, or even using a multiplexer chip. But for temperature measurement, it’s much easier to use digital sensors such as ds18b20. You can connect as many of those as you like to the same digital pin, and yet still read each sensor separately (they use a bus system called “OneWire”).

To set parameters and check readings, you can get the chip to host a simple web page. Or you can use an app called “Blynk”.

PaulRB:
Yes, you can, but only one thermistor, because all esp8266 have only one analog pin. If you need more analog pins, you can add more using external modules like ads1115, or even using a multiplexer chip. But for temperature measurement, it's much easier to use digital sensors such as ds18b20. You can connect as many of those as you like to the same digital pin, and yet still read each sensor separately (they use a bus system called "OneWire").

To set parameters and check readings, you can get the chip to host a simple web page. Or you can use an app called "Blynk".

Thank you both ! I have to stick with the analog pin, so one is fine (at least for now) can you please point me to the correct direction as to how to be able to upload the sketch via wifi?

Just Google for "esp8266 OTH". I have never done this yet, but many others have.

superJj:
Thank you both ! I have to stick with the analog pin, so one is fine (at least for now) can you please point me to the correct direction as to how to be able to upload the sketch via wifi?

to remote update the sketch on esp8266, use in sketch the ArduinoOTA library bundled with esp8266 Arduino boards package