Our house currently has one older gas furnace (40 yrs old) with one set of
ducts that run between the first and second floors. The ducts branch such
that our suite (upstairs) has registers on the floor and the tenant's suite
(downstairs) has registers on the walls. I was interested in dividing the
heating for the house by installing a gas fireplace upstairs, along with
electric heaters in the bedrooms upstairs. We would then close off the
furnace registers such that the furnace only heats the downstairs suite.
I'm wondering if by closing off our registers (either by closing the dampers
or installing something to block the ducts) will we cause problems for the
furnace or for the downstairs suite? By halving the space that the furnace
feeds, will the furnace cycle frequency increase (more on/off cycles) and
thereby cause more wear on the furnace? The cold air return is in our
suite, is this a problem (obviously we won't block off the cold air return)?
What potential issues should I be aware of?
Any other suggestions for how I can create two separate heating zones for
our house? While the above scenario would probably work, it's likely quite
inefficient for the downstairs suite. Probably the best solution would be
to get a new more efficient furnace and install a second run of ducts. This
would be extremely expensive though, I think. If I were to go this route,
are there any required features for the furnace (variable speed fan, dual