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Dutch2 02-28-2010 01:51 PM

Zone damper sticking
My downstairs HVAC system is divided into two zones, the main living areas and the master bedroom.

The damper for the main area occasionally does not open.

I notice this because the temperature drops and only a little air comes out of the registers. I imagine that before I notice this the heater has been going for a while trying to heat the place, so I'm sure this is costing me money.

I can go into the attic and hit the damper and it will open and work OK for a while.

Is this something that can be fixed or should I replace the whole thing?

By the way, I don't really like the zoning system because even with both zones active the bypass damper does not fully close.


beenthere 02-28-2010 02:07 PM

Depends on why its sticking.

Probably needs replaced.

The bypass probably doesn't close the whole way when both zones call because your short on return.

Dutch2 02-28-2010 02:14 PM

I was just wondering if this is something I could lubricate or if this is the normal way these things stop working and it just need to be replaced.

I've been thinking about adding a return in the bedroom so the system works better when the door is closed, so it sounds like this would help it overall.

Is there a way to determine how "short on return" the system is? Can I measure the in & out temperature and calculate this?



beenthere 02-28-2010 02:19 PM

You can try oiling it. But, the motors are generally sealed bearings. So oil usually doesn't help. For more then a little while.

Yes, temp rise with both zone open can tell you how much air its moving. But not if its your return or supply that is lacking.

I said short on return. because that is the usual problem. it is possible that you are short on both supply and return, or just one or the other.

Best way to tell that is with a manometer, and check static pressure of both supply and return.

BTU output divided by (temp rise times 1.08) equals CFM.

Dutch2 02-28-2010 02:33 PM

Thanks, I might try to oil the motor while I look for a replacement.

I looked in the furnace manual and it shows a CFM vs. temperature rise table. It seems if I measure the in and output temperature I can use this table to determine CFM?

I also have a CFM vs. External Static Pressure table for each of the 4 fan speeds, so if I know CFM and fan speed I could determine Static Pressure?


beenthere 02-28-2010 02:49 PM

Yes to your above questions.

But. it works better to measure each individual parameter. to get an accurate CFM.

EG: Check temp rise, calculate CFM. Check static, and check CFM against chart.

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