I have a two story 2.5k sq ft house with a varying degree of temperature throughout the house. The main problem is that the air coming out of vents are very weak if almost nil. Only the living room that's closest to the unit in the garage has full strong air and the rest of first floor and the whole second floor has almost no air coming out. A while ago, we had a minor work done on the duct going from the unit to the wall (to the house). He took off all the insulation padding and sealed the ducts with some kind of putty (I could be wrong I don't know too much about house stuff). I didn't notice much change then and two summers have passed.

I think it's really time for me to do something cuz one month my elec. bill came out to $500. But I don't know where to start or who to call to consult.

Can I reduct throughout with a narrower duct for easier(?) installation? I think there's definitely a leak somewhere because one side of a wall is cold whenever I have the a/c unit on. Hopefully that has each room with stronger air flow.

Then, I want to control each floor separately because temperature difference is too big to just do so with 1 thermostat. I read somewhere that if I wanna do multizone I need to install baffle to direct each flow to each zone. If I can do that much then maybe I can finally install z-wave thermostat with z-wave controlled vents to control temperature down to each room. Is my approach too far fetched? unrealistic? expensive? Sorry for the long messy explanation. Please help.


I would recommend first contacting a home energy efficiency company first rather than an HVAC company. HVAC guys are usually clueless about systemic problems like these and will usually try to sell you a larger unit without diagnosing the true cause of the issue (which is a pain in the neck and can probably be fixed for much less than the cost of new equipment).

It sounds like you have two problems: Poor duct pressure and temperature stratification. These are likely caused by the same thing: conditioned air escaping or being wasted in some manner. A common cause is ductwork running through an unconditioned attic. For example, in a ranch house, if the A/C unit is on one side of the house, the register on the far side will often not be very cold because the heat of the attic is sucking out all the coolness in the ducts!

This is the kind of thing that is virtually impossible to diagnose over the internet. I would recommend contacting a local energy efficiency & retrofit firm.

  • Thanks everyone for great tips! I feel more empowered. I looked into dampers and now am more clear on things. My problem is two folds-duct & zone control. So, I want to take care of possible leaky ducts first. Rather than an entire reducting, I thought about smaller duct inside my existing duct. In Vancouver, BC, I've seen a high end (mom-in-law's) house with a much narrower (maybe 6in diameter at most), white padded(?) duct that ran the house. It was kinda of fresh cuz I was used to seeing only the 1-ft diameter metal ducts. Anyone know what I saw? or better solution for possible leaky ducts? – mcchung52 Oct 13 '14 at 16:54
  • I agree, iLikeDirt. That's why I'm afraid to call anyone. So I want to do a thorough research and know what my options are. As for my looking-into-smaller-duct comment, my assumption here is that going through the entire existing duct, finding leaks then patching them is more time consuming and thus expensive than just running the smaller duct. – mcchung52 Oct 13 '14 at 17:07
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    Using a smaller duct isn't a great solution in my opinion. While it may increase the air pressure now, when you eventually fix the problem that's causing poor air pressure to begin with, it will work against you by restricting the flow. I would find and fix the root cause rather the symptoms. – iLikeDirt Oct 13 '14 at 17:18

If you're not going to do the work yourself, you could contact any local Heating & Air Conditioning company (HVAC). They will be able to find and repair any problems with the system.

As for zoning, it's definitely possible. How easily it can be done; and to what degree, completely depends on your house, and how willing you are to potentially open up walls (if required). To accomplish the task, you (or the HVAC company) will have to install dampers throughout the ducting system. These dampers will then be controlled by a zone controller, which in turn will be controlled by thermostats throughout the home.

When a zone(s) call for heat/cool, the HVAC system will turn on, and the applicable dampers will open to direct air to the desired location. This will provide better control over the temperature in the home, but could also lead to slightly higher or lower heating/cooling costs, depending on the setup.

  • There are also now retrofit duct systems that involve air bladder dampers with small air hoses passed through the duct. This eliminates opening walls. – David Pfeffer Oct 13 '14 at 12:26

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