How many chicks would fit under one heating pad? Assuming the size the OP uses, 12x24 inches, but on a tunnel that will make it something more like 12x18 or 12x12..... if I'm raising 60 chicks, how many heating pads will I need?
Don't make them tunnel-shaped. Make the ceiling flat so you can fit more chicks under the pad than would fit in a tunnel-shaped setup. I agree with junebuggena, divide them into 2or 3 brooders each with their own pad. The 12x24 pad can be found for $15, so it's not a big investment.