Unless it is very cold where you are--like if you have your brooder box in the house, or in a protected garage, etc, a 40 or 60 watt bulb should do it. Keep it fairly low-15 inches or so from the floor of the brooder, and put a thermometer under it when you forst set up, to make sure the temp is at least 90/95 degrees there. But, have it at one end of the box, so if it gets too hot, they can spread out to where it is cooler. Nights will probably be colder than daytime, so be sure to check it at night, when setting it up. I kept a 40, a 60, and a 100 watt regular light bulb on hand, and raised chicks all thru the winter in my garage, which wasn't heated. Temps got down to 10 or 20 F. (-8 to -12 C) at ights, and I had the 100 watt bulb in and they could move directly under it if they got chilly. Warmer days, I switched to the 60 or 40 watt. Much more economical than a 250 W. which I think is overkill, unless you are in a very cold place. I keep the smaller bulbs lower, instead of raising the 250 watt way up so it won't be too hot. Good luck.