Question for residential techs.

[fixerup]

I am an industrial A/C tech. and just moved into a house we had built.Turned on the heat for the first time last night.It is a dual zone system with gas heat.The downstairs was 66F and the upstairs was 75F both T-stats are set at 66F.I checked out the system after calling the installing contractor and them telling me they could get to me in about a week.What I found was the damper for the upstairs was closed but air still came out of up stairs vents. So I took the damper out and found the damper is 1 1/4 inches short lengthwise and a half inch shorter on height than my ductwork. My question is shouldn't this damper seal off better or is it supposed to have some bypass.I should also mention this metal damper and motor are mounted in ductboard with no support. Will the ductwork sag and lose its shape in the future? Sorry for the long post.Any info is greatlt appreciated.

[BobbyBJr]

Yeah, I want all my dampers to seal better than that and yeah, the ductboard will sag over time from the weight of the damper and cause it to bind and not work.

Bobby

[Toolpusher]

I don't install ductbrd, but when i install a metal truckline, I usually leave about 1/4" clearence top and bottom and side to side.
I don't want any drag from the movement of the dampers.

Build yourself a metal sleave to fit inside the ductbrd, and mount the damper your self, with less bypass.

[tinknocker service tech]

how can the damper be held in place properly with out a matal sleeve. it should be tight in the duct work. there should be a metal sleeve about a foot long at least and supported so the duct board doent sag and break apart
i dont work with duct board and dont plan on it either so this is just my opinion only

[wxr]

All the residential zone systems I have worked on the dampers seal tight and have a gasket stop ring aruond the inside of the damper. My ? would be Is the unit a single stage system and the original installers never put a bypass damper in to allow the system to operate on a call for one zone. Wonder if they did that to get it to work when the down stair T-stat is calling and the up stairs is off.

[docholiday]

They might have been undersized to allow minimum airflow when only one zone is calling.

[fixerup]

There is a bypass back to the return.As far as undersizing the damper I don't think so.It is called a dual zone system that should be able to maintain a set point up stairs and a setpoint downstairs within reason.I can live with a 2F difference in zones but not 9F-10F difference.

[docholiday]

Yes but if one zone is calling, your just as well served to allow a small amount into the other zone for three reasons at least.

First, pulling 120 degree air into the return can make the unit cycle on it's limit

Second, if there is a load on the first zone for heat, there is likley some need for heat, albiet less, for the other zone, feeding a small amount of heated air into that space will help maintain it and prevent it from calling for heat less often without overheating the zone.

Third, a bypass damper will supply significant return air in and of itself. This will slow the amount of return coming from the return grills which are out in the home leaving you with poor circulation within the conditioned space.

I almost always recommend some sort of minimum damper position unless there are 4 or more zones where a minimum of two of them are open 100%.

[pecmsg]

Not to add fuel to the fire but just for argument sake and this is a big problem I’ve seen with residential zoning. If the op has a 12 X 20 duct and a 12 X 18 damper, You make a sleeve and block off the extra 2" aren’t you reducing the duct to 12 X 18???

I agree with Doc about minimum air flow but do it with the damper. Minimum closed

[Edited by pecmsg on 10-26-2005 at 09:23 PM]

[fixerup]

I agree if minimum air flow is required then don't let the damper shut off 100%.I thought the dual zone system was supposed to maintain a comfortable temperature in each zone.So far in the heat mode this unit is not making my family very comfortable.