I have to agree with that, a 1000w heater is excessive, even for several turtles. It's best to buy the size of heater (or multiple heaters if the amount of water exceeds the recommended capacity) for your tank, make sure it keeps the temperature at the desired temperature, and it's fine.
For example, a 250w Stealth heater says it's good for 75 Gallons of water, so for most turtle enclosures, you won't fill the water up to the top as you would with fish (unless you construct your own above tank basking area), so it's fine. There are often charts on reputable heater websites, or even on the back of the box that tells you what wattage heater or how many you need if you want to raise the temperature of the water to X degrees, counting in the room temperature as well.
rocketright, I recall in some other post you had a formula of 200w or so per turtle in a tank, this is not necessary, just enough to warm the water capacity of your enclosure is fine. 1000w would also drive your electric bill way up there, especially in a water heater on 24/7.
