Regarding bathroom fans - my bathrooms have regular ceiling-mounted fans, and I would love to swap with a heat recovery unit (they are needing replaced anyway). Are there any drop in replacements? Can you point me at them?
I have forgotten the manufacturers names. For the larger house type units have a look on the self-build sites as they tend to be leading edge for widgets and construction tech. The systems are scaleable with the gubbins being placed up in the attic. Doing a UK/euro house I would only bother doing upstairs areas only as the warm air rises to those areas anyway - and you do not end up with having to try and hide 4" air pipes when bringing them downstairs.
Another interesting widget I saw in Germany was recycling warm air. As we all know warm air rises and 'cos the air rises and we are on the floor we keep pumping out heat to keep us warm. The solution I saw was to have air pipes (around 10cm - 15cm) from a high ceiling back down to floor level with a small PC type cooling fan sucking in the air at the top of the pipe and re-circulating it back down to floor / seating level. I was told it worked very well and saved money - they did baffle me with numbers but, bottom line was they saved money.