A solar pool cover will retain about 90% of the heat. This percentage can and will change depending on what region you live in. If you live in the hot south you will find that your pool will retain most of the heat whereas if you live in Minnesota where it is cooler it might retain 5% to 10% less. As far as generating heat...well, keep your heater. A solar pool cover will generate a very small amount of heat but not enough to where you can give up that heater. The solar cover will, however, probably save you at least 50% in your electricity costs of using the heater. Now I have to go back to the region aspect of these covers again. If you live in an area where it is hot at night (80 degrees or more) you can certainly go without the heater but be aware if the evening temperature drops so will the water temperate and it could take 1 to 2 days for the heat to go back up to where you want it. I hope this information helps but if not and you would like to find out more you can go to PoolCenter.com where yo