How do I mothball my hydronic heating system?
 

Due to changing household requirements, I have decided to mothball my
custom hydronic heating system. This includes removing the "boiler,"
which is uninsulated and occupies a huge amount of precious living
space. A large wood-burning fireplace wrapped with large iron water
pipes heats the boiler; there's a backup LP gas heater, too. All the
water pipes are embedded in the concrete slab; no pipes are ever
exposed to temperatures lower that 40 degrees F. Well, I suppose that,
if the house were unoccupied and all heat sources shut off, a prolonged

extremely cold period could result in mild freezing exposure to one
small section in a closet in the garage.

My questions:

1. Once the boiler is removed, what should I do with the remainder of
the system? I mainly want to prevent corrosion in the pipes and pumps
because I'd like to retain the option to replace the boiler and
upgrade the system. But I realize that this may not be possible after
years of disuse.

2. Is it possible to simply close each of the three zone loops? This
would allow me to run all the pumps occasionally to prevent them from
becoming 'frozen.' Somewhere I read that draining the system is a bad
idea because you can't ever get all the water out and the added air
will accelerate corrosion.

3. Should I add a corrosion inhibitor?

4. What should I do with the fireplace loop if I want to continue
burning wood? I suppose I must remove all the water from that loop and
leave it open or else the water will boil and burst a pipe. Then I
suppose that the extreme heat will boil away any remaining moisture and

thereby prevent corrosion.