Hi all, I have been reading through the posts on this thread and others a few hrs and just don't have time for any more today lol. So thought I should just ask straight up regarding my specific scenario instead to get advice from the experts

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I have 12 chicks about a week old. They are currently inside a room (on average 60-65 degrees). I use a 12x12 heating plate (from Rent-a-Coop on Amazon; looks like a table). This was recommended to me so I bit the bullet and bought it so I wouldn't have to deal with a lamp. Funny I had thought of using a normal heating pad too but wasn't sure how I'd go about it...plus didn't know about BYC at the time. ANYWAY.
We need to move chicks into larger brooder but it won't fit in the room and I don't want it stinking up main living areas so they're heading to the garage soon in a huge produce box (will insulate base from cold floor). Can't go out to coop because I don't have power out there yet- working on it. Temps outside still hit the 20s here at night from time to time so needless to say the garage will be a lot colder than the house.
Would this plate even work out there? And up to what age for 12 chicks to fit? As a newbie I find they were really misleading with toting 20 chicks as description implies - I wanted one and done for the heat source the whole 8 weeks. Sigh.
What should I get for them (and size, for one-and-done, try #2?)? Need to make the move soon. How long do you see my current heat source lasting, if it would even work in the garage? Thanks so much. Chicks doing great so far.