In the late 80s we ran 2 solar thermal panels on our garage roof to heat the pool. If you forget anf left the pump on the pool would be too hot to even get in. Really tho thats over kill and there is almost no need to heat a chicken coop. If its insulated and vented well it will be just fine. Infact id venture to guess more chickens freeze to death from lack of ventilation then from the actually temp outside. Humidity builds up and water removes heat faster then air. If you over heat your coop and the heat source fails in some way. You will probably ensure all the birds freeze to death.