I'm using - and have used - 250 watt infrared heat lamps. I just raise or lower it depending upon circumstances, and I have my brooder in my bathroom. Plus, the Rubbermaid tub is NOT covered.
It doesn't need to be 4 feet above the brooder, honestly. But it is about 2 feet up. I'm able to arrange "zones" in the brooder: really warm, warm, not so warm, cool. As the need for heat diminishes, I just raise or tilt the lamp, and move the brooder slightly. Works very well for me, for (counting) four sets of chicks since October 2009.
The infrared heat lamp can fool you, though; it does NOT heat the air, so putting your hand in the brooder to check how warm it is in there is NOT the way to do it. You have to really observe the chicks to see their response to the warmth and make sure they have the zones for hot, not so hot, cooler.