hvac baffle system

Is anyone familiar with what I believe they called a baffle system? I have one furnace and one a/c unit and 3 thermostats, one for each floor. depending on which thermostat orders heat or a/c, the baffle system opens those ducts and closes the others. My problem is that when it blows it is quite loud at certain ceiling registers and I don’t know if that is the norm. Any ideas or areas to conduct my search would be greatly appreciated. Thank you.

Is the sound always loud at the same registers, or does it depend upon which thermostat(s) are calling for air? I can imagine that there might be a whistling sound when one or more dampers (baffles) is closed, as some air will escape around the damper, be forced to a high velocity, and make the sound. If you are able to determine which damper is the main offender, you can then attempt corrective action, which might include adjusting the damper to close tighter, and verifying that the other dampers are opening fully. If those don’t work, then adjusting the “closed” position of the dampers to be not so tightly closed might help. Those are the only actions that come to mind. Other inspectors may have some additional suggestions.

Jim King

In different parts of the country, it is referred to by different names. Here in Chicago, we refer to them as motorized dampers. As far as the noise; the blower fan does make noise, but shouldn’t be annoying. Older units were loud. Depending on the type of noise, it could mean anything from a loose belt to damaged bearings. I may also just be dirty. You have to decide for yourself if you want to upgrade to a quieter fan.

I hope this helps. If not feel free to add additional information or give me a call.

it appears that the air/heat is being blown very forcefully and creates the noise coming through the registers. hope this helps describe what is taking place and gives you a better idea of what could be the fix. thank you.

Some fans have adjustable blower speeds. You should consult an HVAC contractor to make these changes. If they kicked up the pressure because a remote location is not getting enough air flow, then you have to decide which is more important. Noise or heat.

that would make sense. it is a 1 year new 3 story townhouse and the installers might have tweaked the fan speed to reach all areas. we’ll have that looked into. thank you very much.

in keeping with that thought, the 3rd floor does not seem to have a very long blowing cycle and it is nearest the a/c unit. if it is blowing harder than it should, that area would get the brunt of the faster speed, heating or cooling faster. i believe i read that the unit should run a longer period of time as opposed to a shorter period in order to remove moisture from the air. would this be true?

and, if it is true, could moisture have built up in the ductwork causing a problem there? the townhouse comes out of warranty soon and i’d like to make sure it doesn’t have any major flaws. thank you again.

I am assuming you are a homeowner. If this is the case, the best advice that I can give you is to have this property professionally inspected. You will most likely have a home inspector come through the property when you go to sell the home. That person will most likely find defects that you are not aware of. Since your warranty will be expired, you will be the one who will bear the consequences. You can find someone close to you at the top left of this page.

I would be happy to talk to you on the phone. You can reach me at the number below.

In Canada, it’s known as ZONE heating.
There is also supposed to be another damper which is usually located somewhere on the plenum that lets excess pressure out when only one zone is calling for heat/AC. This usually has an adjustment lever on it for this purpose. Kind of a balancing damper if you will. I don’t know the technical name for it or the specs on setting it though.

From the description it seems you have what is called a “zone dampered system” around my neck of the woods, which is much less desirable to having separate equipment/zones for each area for exactly the reasons/problems you described (and others).

Talk to a local HVAC specialist to see what can be done.


Sounds like a poorly designed Zone System. They should have sized the smallest zone to handle 100% of available air or installed a bypass damper so the extra air the system delivers is dumped back in to the return. The best way to install these types of systems are with 2 stage heating and cooling equipment with variable drive motors sizing the smallest zone to handle 100% of 1st stage air flow. You can try changing the supply air grills with a one way adjustable grill such as the shoemaker 950 series thats the one we use on all zone systems.

As posted by Darrell and Rolland, the barometric (bypass damper) is not properly installed/sized.

It is also likely that the system design is wrong.

Generally you will not find a residential zoned system that can handle just one zone at a time. The HVAC unit must be too small to handle all 3 zones in the worse case weather. The controller can be adjusted in many cases to allow 50% bypass rather than 100% when one zone is operating ect… This takes a VERY Qualified person to set up. So go for the gold and have a TAB Tech correct it.