zoning trouble....

Bigsteve

Hi guys, Less than one year old Lennox natural gas furnace with 3 zone controller. What I have zone 1--800 sq. foot cottage on a lake, southern michigan, not insulated well. Low temps, heavy winds , lake effect snow. Zone 2 --upstairs new addition approx 1600 sq feet Zone 3-- downstairs new addition approx 1600 sq feet. New additions are new construction 2X6 walls , insulated to the max....
Problem is with zoning. If we turn up zone 1 far enough to make it warm, then zones 2 and 3 are exceptionally hot. With the thermostats set at 72 in those zones the real temp can be 78, while its still chilly in the "old" part of the cottage. Yes, I know the proper way to fix it is to add more insulation to the old part. Not really on option in the middle of winter.
When the installers put it in, they explained the furnace is too big for the 800 sq foot cottage and some of the heat has to be "bled off" into the other zones or the heat exchanger gets too hot and could crack. I am aware that this is true. So , when they set it up, zones 2 and 3 dampers don't close all the way allowing some of the heat to "bleed" into those zones, whenever zone 1 runs. Leaving zone 1 chillier than it should be and zones 2 and 3-- 78 while the thermostat is set to 72. So to fix this I could 1--Start tearing out walls and re-insulate zone 1 or option 2 --reset the dampers to where they don't bleed off as much heat and hope the heat exchanger doesn't melt, or perhaps you guys have some ideas?

HVACNUT

It should have a barometric bypass to compensate for partial load and a DATS, discharge air temperature sensor. The zone board should have DATS terminals.
Even better if the furnace has an ECM motor.
I dont know how the linkages were adjusted on the dampers to not fully close. That's not typical.

Bigsteve

Thanks so much for the response, merry christmas!. I will research the bypass and dats and see if it's something I can do myself, or have done for me. Ecm motor is something i will have to research also. At least i have a place to start now.
And yes i just looked at the damper motors, they do not return all the way back to the closed position. That is where they made the adjustments. Thanks for any and all help, much appreciated

John Mills_5

They were probably trying to keep the furnace from short cycling. It should have the DAT to keep the furnace off its own limit as the furnace limits like to stick open if they open too often. But if you fully close the other 2 dampers, even with a bypass, you'll increase the short cycling which costs gas usage and shortens the heat exchanger life.

EBEBRATT-Ed

I think your stuck with what you have and need to insulate the "old section" You zones have very different loads.

The installer is correct you do need enough airflow to not damage the furnace heat exchanger. Weather it's done with a barometric damper or by keeping the other zone dampers at a minimum position doesn't matter. The bleed air needs to go somewhere.

What should have happened was a second furnace for the old area would have worked better

ratio

I've thought, off 'n on, about zoning with inline fans instead of dampers. Use a RIB relay to switch a booster fan, using the wind open contact on the zone board.