Zones and Air Balancing

Problems related to residential installations.

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Zones and Air Balancing

Post by Logan46 » Mon Jan 17, 2011 7:04 pm

When we had our house built last year, we specified separate controls for a small parent suite (421 sq ft) and master bedroom suite (511 sq ft). What was installed was a unit with 2 zones. One zone for the parent suite and 1 zone for the master bedroom suite, which also included an adjoining bedroom (145 sq ft).

The initial problem was too much air and noise in the parent suite. The HVAC installer installed a bypass(?) to reduce the air flow. The problem then was hardly any noticeable airflow in the master bedroom suite. A second service call resulted in the fan speed being increased, but I still could not feel hardly any air coming out the registers from 4 feet away (standing on a chair with 10 ft ceiling).

During a recent cold spell, our master bedroom suite and especially bathroom were cool. We normally set the thermostat back 5 degrees at night. It will take almost an hour plus of constant running to bring the Master bedroom suite up 5 degree, whereas the rest of the house (2300 sq ft) on the other unit takes 15 to 20 minutes at the most and always feels toasty.

What I don't understand is why they installed a bypass which to me just re-circulates already heated air over and over instead of putting all out into the ducts--that would seem to be very inefficient. Secondly, the unit has a Honeywell TrueZone electronic controller (?) which I thought was supposed to automatically balance the air flow to the different zones.

The furnace in question is a Lennox G40UH-36A--070 with an output of 53,000 BTUH.

I know next to nothing about HVAC but what little common sense I have tells me something is not right. Please help educate me so I can deal with the installer intelligently instead of being confrontational. Why do they sell zoned systems if they don't work? Many thanks in advance.

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- Zones and Air Balancing

Post by nomadpeo » Thu Jan 20, 2011 6:16 am

i agree with the duke. the only thing i would add is that there are limits where zoning is concerned. the reason there must be a barometric bypass damper is to maintain a reasonable cfm of airflow through the system when motorized dampers close off some of the ducts. the bypass damper must be sized appropriately for the smallest zone so that when that is the only zone calling, the balance of the required cfm of air (350 to 400 cfm per ton) is recirculated to maintain proper airflow. it is possible the damper is the wrong size. an imbalance can cause problems with the refrigerant system as well.

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