Greetings & Salutations. Welcome.
I have used a heat lamp but make sure it is secure ( I applied extra clamps) and put an old screen on top of the brooder, so it cannot fall into it.
Also, depending on how many chicks, you can use/make a Mamma Heating Pad/MHP. If you do this, you will want a heating pad that Does Not have an automatic off. You want the heat on all the time when the are young.
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