*
A few years ago at the same time I had central AC installed in my house, I had the contractor put the two second floor bedrooms on a seperate zone. A seperate thermometer was installed in the master bedroom and opposing blade dampers were installed to control each zone. This has alleviated the problem of over heating or under cooling the second floor of the house.
The problem is that when the first floor calls for heat and the second floor does not, I hear a “humming” noise which seems to be coming from the second floor damper. It’s as if the air that is blowing up to, and then being stopped by, the damper is causing the damper blades to vibrate. The condition does not exist if both floors are being heated or cooled at the same time nor if only the second floor room is being heated or cooled.
I would appreciate suggestions on how to solve this problem. Is there a differet type of damper to use, perhaps?
TIA
Replies
*
You provided no details on the dampers that are installed, like manufacturer and model, but I have few questions. Does the first floor damper do the same thing when it is closed and the upstairs is open? Do the dampers have any provisions for a minimum position setpoint or a stop? If they are accessible, check and see if there is a stop. If there is make sure that they don't completely close, they're not designed for that anyway, but may be trying to. If you can establish a minimum flow, the vibration or humming will stop. There are dampers available that will close tight and not leak or vibrate.
*You do not say whether the damper defaults to the open position when all power is off to the damper, most manufacturers models do. The damper closes when there is not a demand for heating/cooling, in other words the damper motor is energized when the damper is closed. You can check this by disconnecting the power to the damper motor when it is closed, the damper should default to the open position and the humming should stop. I had this happen on my house same humming, I replaced the damper motor and I have not heard a thing for about two years now.
*They are TrolATemp Automatic Opposed Blade Dampers, the only model number I see is 45/97 (not sure if that's a model number or some kind of date code).To answer your questions Tim: No, I do not get the same noise from the first floor damper. It only happens when the first floor is being heated (or cooled) and the second floor is not, ie. the first floor damper is open, second floor is closed. They are accessible, can you tell me what a "stop" would look like or where the adjustment should be? I see the arm and the motor with the connections on top. They are then wired to a control box on the furnace.Can you site make and model of the other dampers you're referring to?Thanks,Pete
*The damper control box has a switch that lets me switch the default for each damper to open or closed. The second floor damper defaults closed.I do not believe that this noise is from the motor because, as you say when the damper is open there is no humming. When it is closed there is humming but which I believe is the blades vibrating by the air it is (correctly) stopping. By opening the damper the noise stops but leads to the original problem...too much heating or cooling of that floor, which is the reason for the zoning in the first place.Hopefully I made that somewhat clear :)Pete
*Look fore stops on the control arm that operates the damper. These could be a set of cams with set screws that pick up a microswitch, or adjustable linkages that only allow the control to rotate so far in one or both directions. If the system has electronic controls, look for a graduated set point dial or screw.Tim is correct in that most dampers are not meant to close 100% unless there is a way to relieve the excess static pressure that builds up in the duct, or you air handler has some type of variable fan speed control. Without one or in some cases both types of controls you could split the duct work open with excess pressure.Dave
*The damper manufacturers that I am familiar with are Ruskin, Carnes, Nailor and Greenheck. There are others. They all make leak tight dampers among other products.I think Dave described pretty accurately what I would look for in the stop.
*> Tim is correct in that most dampers are not meant to close 100% unless there is a way to relieve the excess static pressure that builds up in the duct, or you air handler has some type of variable fan speed control.My fan is, unfortunately, single speed. This may sound crazy but I'll ask anyway, what if I drilled one or more say 1/8" holes in the supply duct just before the damper to alleviate this pressure. This supple duct goes up to the second floor in the garage and a "heated" garage would not be a bad thing! Is this a stupid idea?Pete
*No, not a stupid idea. A small boot take-off and a register would be better than drilling holes in the duct. Find a way to keep the damper partially open.
*Sounds like a good idea. I'll try it. Thanks Tim and all who responded to my question. Happy Holidays, Pete
*I'm about to zone my HVAC system in my 2 story house with forced air furnace in basement, trunk line to attic with ceiling vents to all rooms upstairs. Another trunk across basement with vents to all main floor and basement. I intend to put dampers in both trunks to control 2 zones. The basement and first floor will be on the same zone (basement controlled with manual register dampers) Would it be worth the added expense to make the basement a separate zone? I assume it would require register dampers on both floors as they are supplied by the same trunk. Also should the damper for the 2nd floor be in the attic (duct board trunk in attic and easiest access. as opposed to metal duct from plenum to attic.)
*Ron,Two things are important when determining zones in any HVAC system; use and exposure. If you use your basement differently than your first floor, you may want to zone it separately. But your basement being supplied by the same trunk line as the first floor will make that less than practical.To be sure were on the same page here, in most residential systems, there are registers and there are branch dampers. I would do as you planned. If you have branch dampers, open all the registers fully and adjust the flows in the branches (within a zone) using the branch dampers if you have them, then you can open and close registers to fine tune or as use changes.Locate the (zone) dampers where access permits. All other factors being the same, closer to the unit is better. The reason being is that the dampers will have better control closer to the unit where the pressure in the duct is higher and the noise of air squeezing through the damper at low demand will be less noticeable.
*Thanks for the reply. Now one more question, do you have a preffrence as far as zoning equipment? Dampers,thermostats,controlers.
*Look for an integrated system unless you have the means to assemble a system from components. If you are going to do this custom I would recommend Honeywell controls and, Ruskin dampers.
*
A few years ago at the same time I had central AC installed in my house, I had the contractor put the two second floor bedrooms on a seperate zone. A seperate thermometer was installed in the master bedroom and opposing blade dampers were installed to control each zone. This has alleviated the problem of over heating or under cooling the second floor of the house.
The problem is that when the first floor calls for heat and the second floor does not, I hear a "humming" noise which seems to be coming from the second floor damper. It's as if the air that is blowing up to, and then being stopped by, the damper is causing the damper blades to vibrate. The condition does not exist if both floors are being heated or cooled at the same time nor if only the second floor room is being heated or cooled.
I would appreciate suggestions on how to solve this problem. Is there a differet type of damper to use, perhaps?
TIA