nostr:npub1yacj26q9parem5fqf2s3ym9xkxghkk0w2jc63aglsnl2fmyhshnszgla7e nostr:npub163w0x42e9v5halescch6sqe3k4lzmjlghsqpejapgfnmeucjnekshmlq6z nostr:npub1lllv638gr9ax6uaf3n3hy4aqp5e7pvrmz6g68x6rckuh7urx75dq5k5409 There are two main downsides to them:

1 - as of now, they're quite expensive.

2 - because they're a single unit, the fan that drives the air over the heat exchanger is part of the unit. Therefore, it makes a noise.

It's noisier than a gas boiler, but not massively so. If you have it in an airing cupboard then you can ignore it. If it's out in the open, it may be annoying.