I don't know where you are or what you mean by cold. That can make a difference.
At a month old they should be real closed to feathered out. Most chicks are fully feathered out at 4 to 5 weeks. After that, in theory, they don't need any supplemental heat. If yours have been kept where they are always warm, I'd wean them just a bit. Maybe set up a heat lamp in their area where they can go to it if they want to. Maybe put a shallow draft guard inthe area so when they are laying down they are out of any possible drafts. But make that area is big enough that they can move away from the lamp if they get too hot. And be very sure to throw that clamp away and use wire or something that will very securely support that lamp. You do not want to cause a fire and those clamps are extremely unreliable.
With 30 chicks, they will sleep in a pile and keep each other warm. That by itself makes a big difference.
I start mine in a brooder in the coop from Day 1. I keep one area warm but leave the rest of the brooder to cool off quite a bit cooler than the recommended temperatures. They spend a lot of time in the cooler areas and go back to the heat when they need it. I take the brooder and heat away at 4 to 5 weeks, but that is during a warmer part of the year. It does get down to the upper 40's, but not down to the 30's when I do that.