They’re in a big tote with a heat lamp right now and it’s great but as they get older it’s not gonna work. Any tips on how I should set up the garage for them? How many heat lamps I should use? Should I use the usual pine shavings or should I use hay? Should I put a tarp down?
I also use a heat lamp. I strongly recommend you do not use that clamp that comes with it. Hold it into place with wire or chain, supported so it cannot fall. As far as I'm concerned, firmly supporting the heat lamp so it cannot fall eliminates the vast majority of the risk of a heat lamp. I'll repeat that. Do not use string that can burn or plastic that can melt or that clamp that can fail, use wire or chain to secure it firmly
I don't know how big your tote is but a good way to get a bigger brooder is to get one or more appliance boxes, maybe from an appliance store. You can tape two or more together to make it really big. Put plywood or cardboard on the floor so their poop doesn't stain your garage floor. A tarp could work. Pine or aspen shavings, hay, straw, dried leaves, lots of things could work for bedding.
What you want is to keep one spot warm enough in the coolest temperatures and one spot cool enough in your warmest temperatures. It doesn't matter how warm one spot gets as long as they can go to a spot that is cool enough. It doesn't matter how cold one spot gets as long as they can go to a place warm enough. I don't know what kind of temperature swings you get in that garage or if it is climate controlled so it stays the same temperature. My 3' x 6' brooder is in the coop. I put chicks in there straight out of the incubator whether we are having a summer heat wave or it's below freezing. In the summer I use a lower wattage bulb on one end. In winter I use two heat lamps on one end in case one fails but there may be ice in the far end. The air temperature may go from below freeing into the 70's F in a few hours. If the chicks get warm they move to the cooler end. If they get cold they move to the warm end.
I don't worry about raising and lowering the lamp on a daily basis. I pretty well set it up when I start for the season I'm in and leave it. I let them micromanage their heat, sure makes my life a lot easier and they know better than I do if they are warm or cool. To me that's part of the problem in using a heat lamp with a tote, it is so easy to overheat the entire tote. Extra room in the brooder is nice for different reasons.
Most chicks are fully feathered around 4 weeks but not all chicks develop the same. Some can take longer. That's one reason I hate to give a firm age for anything like this. The quality of your coop matters too. If you have good ventilation and good breeze protection where they are they can handle pretty cold temperatures much younger than many people expect. It helps to acclimate them to colder temperatures. Mine get acclimated in my brooder, people would be surprised at how much time they spend in the colder parts of my brooder after they get a little age on them. If your garage has temperature swings and you allow parts of your brooder to cool down yours can get the advantage of acclimating too.
There are a lot of "if's" involved but yours can probably go out to the coop in your expected weather at six weeks. They don't have to, it won't hurt them to stay in the garage longer if you can stand it. But you do have that option.
If you can safely provide a warm enough spot in the coop, whether with a heat lamp, heating pad, or heat plate (some heat plates are not rated for below 50 F, you might want to check) you can move them out now.