You aren't heating the brooder. The brooder should be on the cool side and of ample size that the chicks can shed excess heat. The heat source only acts like a small heater for the chicks to warm up under. And all the conventional heat guidelines are wrong, calling for much higher temps than is good for the chicks.
You will gauge the heat in two ways. One way, the more important, is to watch your chicks. If they are desperately huddling together under the heat, they are cold and need it to be warmer. If they are scattered to the far extremes of the brooder and possibly panting, they are dangerously hot and there is no room for them to shed heat. In that case, you need to raise the heat source.
The second way, but not as accurate as the first, is to lay a thermometer on the floor of your brooder directly beneath the heat source. It shouldn't be warmer than 85F in the first week, especially if you are brooding indoors where the ambient temp is also warm.
Then you can lower the temp by around 5F each week thereafter. But watching the chicks' behavior is your best gauge. Here's something not many people know - by age three weeks, chicks don't need any heat during the day. By age five weeks, they are done needing heat and can move into the coop.
I assume you are planning to use a heat lamp. There are better methods of heating chicks now. I urge you to explore them. They are all much safer than heat lamps and carry less risk of the chicks getting overheated and dying from it. Here's one.
https://www.backyardchickens.com/th...d-in-the-brooder-picture-heavy-update.956958/