====== ota ======

===== ESP does not have enough space =====

<code>
ERROR Error binary size: Error: ESP does not have enough space to store OTA file. Please try flashing a minimal firmware (remove everything except ota)
</code>

It is great chance that ESP8266 is equipped with 1M flash. So change board definition in yaml 
from
<code yaml>
board: esp01
# or
board: esp8285
</code>

to

<code yaml>
board: esp01_1m
</code>

or for 4M to
<code yaml>
board: d1_mini
</code>

===== minimal firmware =====

<code yaml>
esphome:
  ...
wifi:
  ...
esp8266:
  board: ...
ota:      
</code>

===== detect real flash size remotely =====

<code yaml>
debug:

sensor:
- platform: template
  name: Flash Real Size
  lambda: |-
    return ESP.getFlashChipRealSize();
  update_interval: 10s
</code>