Charlie Stross (npub1yac…la7e) SuperMoosie (npub163w…lq6z) npub1lllv638gr9ax6uaf3n3hy4aqp5e7pvrmz6g68x6rckuh7urx75dq5k5409 (npub1lll…5409) 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.