We have a solar blanket, our neighbors heat their pool with an electric pool heater. The months they heat their pool they told us the electric bill increases by about $100/month. (And we live in the low Yuma desert where winter temps only reach a chilly low of about 55-60 degrees) Our solar blanket extends our swimming season to about four weeks earlier and six weeks later than not having a blanket. We don't have a blanket roller--looks like a paper towel roller turned on it's side--so the dragging of an 8 Mil blanket across the decking each day caused it to last us barely 2 seasons. The blanket also only heats the top half of the water, so when you get into the pool the top half of the water is REALLY warm & the bottom half is pretty darn cold--it requires some mixing up. We still think it's worth it. We wouldn't recommend going less than 8 Mils.