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Ducts/Dampers question for residental home.

1K views 8 replies 5 participants last post by  bobinphx 
#1 ·
My two story home in southern calif was built in 1965 with forced heating only. I moved here in 1986. I fixed all the leaks in the existing ducts when I moved here. The ducts continue to work fine.I am intending on adding a new heating and air conditioning unit in the upcoming year. I have replaced about 25% of the ducts in one area since I have lived here. The ones that were installed in the house when it was built are a thinner gauge material and I went with a little heavier gauge considering the labor was free with me doing the work. I had always intended on getting air conditioning but could not afford it. Is there a benefit to replacing the ducts with a heavier gauge metal especially when cold air with be running through them with the addition of A/C?
Every room in my house has the original damper in the ceiling to close the duct and keep the heat out of those rooms when there not needed or not in use. Will I have the ability to use the dampers in the same fashion with cold air as I currently do with heating. Or do the dampers have to be wide open all the time with air conditioning? Thanks
 
#4 ·
There is no differance.
Ever looked at them in the store before? There sure not marked hot and cold.
Same physics applys to move the air hot or cold until the air leaves the defuser.
 
#5 ·
I should explain my line of questioning. And I do understand there is no hot or cold on ducts. In just about every house I have been in with air conditioning it always appears that the damper is always open in each room and it is just directing the flow of air. Meaning a whole house is being cooled down while the unit is on and the occupants might only be in a couple of the rooms which obviously becomes very costly. In my 5 bedroom house where I live alone I am able to close the dampers in all of the bedrooms I never go in and the heater works more efficiently and just heats the rooms I spend most of my time in. I assumed A/C could be used in the same manner but I was not sure. I figured the thermostat would shut the unit off when the temperature reached the setting. It seemed to me that as long as the thermostat is in the area that is cooled all the time then it would not matter if the dampers were closed in other rooms.
 
#6 ·
The return air vent would also have to be in the cooled rooms.
That works to a certin extent.
If those room are getting really warm that the vents are close in it can radiate into the other room though the walls and under the doors.
Not a big deal though, it's done all the time.
 
#7 ·
Free flow of air though the equipment is the thing thatactually controls the cost of operation.
shutting off the air in rooms only puts more stress on the equipment.
The dampers at the registers will not in any way control costs.Balancing dampers on the other hand can help balance the house out.
 
#8 ·
The A/C may or may not freeze up if you shut off all the registers in the bedrooms. You may or may not be harming your furnace when you are doing that in heating mode.
 
#9 ·
so you ask, How doI know if I am harming my ac or heater by closing off rooms???

static pressure. you will need to measure or have the measurement done. Your furnace or hvac system will have a max static pressure listed on it or in the manual. Exceed the max static pressure and you will shorten the life of the indoor blower motor and the possibly the compressor.



you can also check the delta t of the in comming and outgoing air.
There are scientific methods to caluculate the delta t, but the rule of thumb is between 15 and 20 degrees of cooling, after the system has been running over 10 minutes.
 
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