Hiya,
you can use BD91 to control any number of the zones (up to the max of 12).
The BD91 can be added as a few types of zone (note you'll need a separate thermostat to get the zone temp):
- Electrical underfloor - it just switches electrically
- Zone valve - it switches electrically (to operate the valve) AND requests heat from the boiler
For any of your zones use the second option, this'll then mean they'll pull for heat from the boiler. You say you don't want thermostatic control in some of your zones, how come? Surely it's better to keep them regulated rather than full heat continuously?
I'm about to get UFH (CH based) in my kitchen and this will also be done using a BD91 rather than the very very expensive HCC80R - this is because the UFH kit I'm going to buy (from these guys
www.theunderfloorheatingcompany.co.uk) already has a mixer and pump, so all the BD91 needs to do is know when to request heat from teh boiler, the UFH kit then does the mixing.
Hope that helps
thx