This past winter I used a heat lamp in my coop anytime it got really cold (generally 100-150W, but did break out the 250 on a few nights) for my girls, and they weren't even chicks anymore...lol. I think maybe it raised our winter bill around $10.00 a month. When they were using the 250 full time last fall (as chicks), it was probably about $15 for the month. Electricity in our area is fairly reasonable. We did compare bills to last years, and they weren't much different, even though last winter was much milder than this year????