I want a cheap, and eco friendly way to heat my 12' diameter, and 4'2" height, above ground garden swimming pool, using the firewood that I have access to. I was thinking of having a firepit, built in to the ground, near to the pool, for sitting around, and wondered if I can also utilise the heat of the fire to heat the pool.
I have electricity and a cold water tap near the pool, and a basic pump and sand filter for keeping the pool clean, as well as a solar blanket for keeping the heat in, once the pool is warmed up.

Heating your pool with firewood is a good idea but,. you would have to have a pipe and water connection under the pool in order to heat it.

You are almost thinking of the way the Romans heated their floors and houses in Britain during the cold winter months. They had furnaces, wood as fuel, and a hot water system under their floors, (pipes made of terracotta) but I am quite sure it would not be cost effective now and a constant supply of firewood would have to be used in order to keep your pool warm. Stay with your solar blanket, it is much cheaper !

Tick

This may give you some ideas

H2oFun ECO Wood Burning Swimming Pool Heater (http://www.h2ofun.co.uk/wood-burning-pool-heater.htm)