Thats a good question - while I certainly wouldn't recommend it, I do understand that fireplaces are really important to a lot of homeowners. So yes: we can and do build fireplaces into our Passive House projects. There are a couple things to keep in mind:
- The firebox should be airtight with good seals on any doors / hatches.
- The firebox should have its own dedicated combustion air and never use the room air for combustion. Along these lines - we'd never recommend an 'open' wood fireplace in a high performance air-tight home.
- With a Passive House, due to the very, very low need for heating you'll likely overheat the space pretty quickly even with a small fireplace - so be prepared to open a window or crack a door if you have 4 or 5 people over and a fire going. It'll get warm in there!
But the short answer is yes, although you do need to think about it and design it in carefully.