m Ransley wrote:
In summer I partialy block off my 1st floor return to increase second
floor pull.


First, I would check all the ducts and returns to understand what's
there and make sure it's all connected. Very common to find tape
that's come off and a duct that's become seperated.

Then figure out how the ducts are run and which downstairs registers
are on the same ducts as upstairs. Then you can try closing off a
couple downstairs registers where it's likely to do the most good in
providing additional flow for upstairs.

Also, check out the size of the upstairs returns and make sure they are
open. Try taking off the grills for a couple of days. I did that and
it made a noticeable difference. Inspect the returns. These typically
use the bays between walls for passage and some times they aren't
completely open, due to poor installation and the installer having not
made complete cutouts all the way along the path, etc.

I agree with the advice about possibly adding another return, or larger
grill opening, if possible. Consider adding a radiant barrier in the
attic, which can help.

There also are booster fans, of 2 types. One gets inserted into the
duct serving upstairs in the basement and is wired into the furnace
blower. The other sits over the register, has a sail switch that
turns it on. I installed the first type on my system and it made a
noticeable difference, though it's not a total solution.

Unfortunately, I agree with Joseph that the best solution is a multiple
zone system. Many of these single zone systems would work better if
the installers did the job correctly during construction. But too
often there are not enough returns, supply ducts for upstairs and it's
very hard to fix later.