HVAC Question (multiple thermostats on one system)
 

Hello,

I have a question about how to handle a tricky thermostat situation.
I'll describe the situation simply below.

My house is located in Maryland and is pretty big. There is a main
floor with 10 ft ceilings and an upstairs, which is much smaller and
has 8 ft ceilings. There are only 2 bedrooms and one bath there. The
style is Georgian Colonial. Anyway, there are 2 separate furnaces / AC
units. The bigger one supplies around 3/4 of the main floor (the
central rooms, the foyer, and one wing of bedrooms). The other unit is
slightly smaller and supplies the other wing, which houses the kitchen,
DR and steps up. It also supplies upstairs.

We'll focus on the second unit. The other parts of the house are
fine. The weird thing about this set up is the fact that the smaller
unit has two thermostats, one upstairs and one on the main floor in the
DR. There is a switch to specify which one on the furnace.

This becomes a problem however, year-round, because of the rising and
cooling of heated/cooled air. In the winter, if the upstairs is
naturally warmer, and if you leave the thermostat up there on 72, then
the downstairs stays cold. If you use the downstairs thermostat, then
the upstairs becomes a sauna.

On the flipside, during the summer, if you set the upstairs thermostat
to 72, it will never achieve this, due to a slate roof, and attics with
only decorative vents for ventilation. While the AC unit battles with
the upstairs during the day, the downstairs gets very cold, often too
cold, and the electric meter spins like a radial saw through our
wallets. If you use the downstairs thermostat, then the upstairs
remains an uncomfortable 85+ degrees.

What can be done to achieve balance in the situation? Should the
upstairs be isolated from the downstairs? Currently there is only a
flimsy sliding door that slides into the wall, at the top of the steps.
I have a feeling other houses have to or have had to deal with this
problem, so if anyone has any advice, please, let me know!

On 1 Jun 2005 18:12:13 -0700, someone wrote:

... The weird thing about this set up is the fact that the smaller
unit has two thermostats, one upstairs and one on the main floor in the
DR. There is a switch to specify which one on the furnace.

Looks like somebody cobbled together a 1/2 arsed "solution". Having
found that the two floors did not behave consistently, they wired in a
"selector" so that they could get at least one of the floors to a
controllable temp.

It is very common, since heating and cooling loads are often NOT in
proportion, for single upstairs/downstairs systems not to balance
properly.

You need some zones, dude. That little upstairs is its own world.
Whether you would have success serving that downstairs part from the
other downstairs system instead, I dunno. But the way your house is
split, essentially horizontally, sucks.

Or is there any way that yo could, seasonally, rebalance the system?
For example, my mother's cheap condo had a single system for two
floors. Every Spring we would shut off all the downstairs registers
and open all the upstairs. And vice versa in the Fall.

Either re-zone once and forever, or re-balance every year if you can.


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