If you’re in the U.S. you may even be able to get a free (or at a substantial discount) commercial heat exchanger later this year: https://www.hvac.com/resources/inflation-reduction-act-heat-pump-rebates/ Not quite as fun as the DIY version though!

If you have some technical ability and are on Android I’d setup sshd on the phone (there are various apps to do this easily) and use rsync(1) or scp(1).

If you want something less technical, I use the Conversations app on my phone and Dino on my desktop for chat and sometimes send files to myself. Not ideal, but it does work pretty well for one-off smaller files.