Ok, thank you. So sending BTC from a Trezor should work just fine, correct?
Yes if it has static bitcoin address.
But how exactly do you receive the Heat tokens? Do you have to sign a transaction? I assume the tokens won't be running on the Bitcoin Blockchain

We'll arrange the token redemption process that for Bitcoin users will include either signing a transaction, or another messaging solution on the Bitcoin protocol. Any way, it'll be made simple enough and if you have access to the sender Bitcoin address you're covered.
HEAT of course has its own blockchain in which the HEAT tokens exist (even when the HEAT client supports access to BTC blockchain also)