Cold Air from Heat Registers

I have carrier forced air heating system (Upflow furnace). There are two heat register in the living room and one in the kitchen that actually are not working (no heat is coming out from those register but sometimes I can feel little cold air draft). All other register are working fine.
I called an HVAC technician to have him look into it. He checked the furnace and as per him furnace is working fine. He popped a mirror with flash light and try to look into the ducts and he could not found any blockage. As per him nothing is blocking inside the duct he checked the flapper on the duct work and it was fully open. He increased blower speed (by exchanging red and black wire) so that air can get more push and told me to reverse the wires back to the original position in summer.
Still there is no hot air coming out from those register..finally I have been told that it could a crushed pipe (duct) in the slab which will take thousands of dollar to replace.
I just bought this home four months ago and not sure what should I do now.
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Is this a recent occurrence? Is it a new house? If the registers have never worked properly, you might see what remedies are available with regards to hidden defects. Laws and regulations vary from state to state. If it's a new house, the homebuilder sometimes has a warranty.
If you're on your own with this and don't expect any financial help from seller or homebuilder, then the next thing I would do is have the register ductwork scoped. There are companies that have flexible snakes with cameras attached. The service may cost you a few hundred, but finding out the problem may be worth it. It might be worth your while to find another HVAC company, seeing as how this one seems to have just given up after some half-hearted measures. Switching the blower speed and telling you to "switch it back" later would not be a good fix even if it DID help. Call around, and you may find a HVAC company who has a snake or works with a 3rd party who has one and get the service call done with one company.
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House is around 15 years old. It is hard to believe that the actual duct pipe under the slab might have crushed. I think it was working fine when I had home inspection done. suddenly something happen..?
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If it's goign to cost that much, or even a hundred, how about buying a camera, etc. That way the OP will have the camera for other uses when he is done. Don't need a wireless camera, but do need some sort of lighting.
If you do this OP, plan in advance how you are going to get the camera not just into the duct but out of the duct too. You might want to mount it inside a funnel, the nozzle of which points back to you, with a snake to push it away from you and something firmly attached, like a strong piece of nylon twine to pull it back. Maybe you'll need part of a 2nd funnel, the cut-off top part, glued top to top to the first funnel, to get past some of the obstructions, that is mostly where duct sections are connected, especially at corners.

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All the vents on the first floor are in the slab (except one in the bathroom) I have total seven vents on the first floor out of these three are not working..one in the kitchen and two in the living room. I tried to ignore this but when I had guests..someone he made a sarcasam that I am really trying to save my heating bill...except those three all four vents are working fine with very hot air. I am going to call a HVAC contractor and finding out someone more comfortable with the duct work.
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Some HVAC ducts have flap/dampers built into them somewhere along the run. They're often controlled with a wingnut. If the ears are parallel to the duct, it's open, crosswise, it's closed. Maybe check to see if you have any-- and that they're open?
Edw.
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I do have wingnut flappers...they are parallel to the duct and it is open
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I'll stand by my original thought then: call a different HVAC company. The one you had out there doesn't sound interested in helping you. Ask if they have the ability to snake a buried duct to see if there are problems.
If a duct had collapsed, I would expect to see some evidence of that in the slab, like a crack or hollow. Ducts don't just suddenly collapse by themselves. There has to be some kind of outside force to do that, and if it's surrounded by concrete then the concrete would show signs of this. I would be more inclined to think that the damper ( or "flapper" if you like) is possibly broken and stuck in the closed position, or maybe broken off and wedged downstream, or some piece of insulation or debris is wedged somewhere.
A thought just occurred to me: take a screwdriver and remove the register cover and take a mirror on a stick and a flashlight and look down past the register elbow as far as you can. This is something you could do before spending any more money. If you see an obstruction, then you have to determine how far downstream it is and how to get it.
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louie thank you very much for your reply. I sincerely appreciate it. I used a flash light and mirror I do not see anything blocking the duct system. but there is an issue with it I can't see more than 3 feet inside the duct and portion of duct system is passing right below kitchen cabinates and stove so I suspect something burried there...
No sign of cracks of damage to the slab from the outside..I agree with you that might be a flapper has falled and blocked that section of the duct work.
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Wonder if those are cold air returns? They might be there to suck cold air back to the furnace.
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I would think that a cold air return in the kitchen would be VERY unusual. I've seen some....ummm... 'creative' work in the two houses that I've owned so far, so nothing's out of the question, but I was under the impression that returning air from the kitchen was a no-no (distribution of grease and cooking odors, etc.).
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You may well be right -- I don't know much -- but if you put the warm air in the kitchen, won't the cold dirty kitchen air just go through the dining room to get back to the furnace? Why would that be better?
I don't have any outside leaks in my kitchen, and the hot air comes out at the sliding glass door, so the current is away from the door and towards the dining room.
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I do not know more but I am pretty sure that those are not cold air return. In my house I have only two returns, they are white colored and near the ceiling. Loiue and mm, HVAC contractor is coming tomorrow morning (Saturday) and he is brining camera to look inside the ducts I will let you know by posting it here or by e-mail.
Thank you for your valuable time and helping me out.
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Hey, hopefully it's an easy and inexpensive problem. I'm curious to know what's happening in those ducts, so keep us informed. Thanks for the feedback.
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Louie and mm, The HVAC contractor came on Saturday..He put the camera ( they use camera for the duct cleaning work) and found no blockage inside the duct. He recommened to put a diverter inside plenum and reinsulate the duct work.
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interesting, so these ducts must have never worked properly? Sounds like poorly designed ductwork then. A deflector will probably help some, but a proper fix would probably involve replacing the main supply trunk with something the distributes the flow a little better.
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Louie, does duct booster work in this case? Just curious
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I have no experience with the boosters. Most of my ductwork experience (very limited) was with industrial solvent dryers for paper coating machines and with smoke hoods on plastic extruders. My only residential experience has been replacing some of the ductwork in my current house.
Duct-booster seems to me like a band-aid solution. It might help, but I wouldn't treat it as a long-term fix. Really, I think what you probably need is someone who knows HVAC ductwork to check over your system and make the necessary changes. I would guess that the majority of the work would involve the supply and return trunks. If the contractor you had out there does ductwork or has a subcontractor that does, ask them for a quote to check the whole system and fix it up. Might only be a few hundred to do the job. I just had a new furnace installed and the contractor put in new, properly sized supply and return trunks for $300 (of course they were already there doing the furnace install so that probably helped with the pricing).
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wrote:

I don't think I have such things (but I'll look some day.)
If you have them, maybe one is broken. Is that possible?
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wrote:

LOL. That's not important. The important thing is that he switched the wires and you get to switch them back in the summer.

How much air is coming out of those vents?. There is probably a good way to measure this, but what is your estimate? Is it as much as the other vents with warm air. Is it more now that the fan is running at a higher speed? IF it has as much air coming out as the other vents do, it's not a crushed duct, duh.
The duct is in the slab? Are the ducts with warm air also in the slab? As much? Did these vents ever give out warm air? You don't say. You don't say how long you've been in the house or how long there has been a problem. (see below)

Oh, you do!!!. So the bad vents have never worked.
Are these three ducts connected close together, so that you could put a booster fan in that would boost all of them.
How about just ignoring the problem. The living room and kitchen will be a little colder than the rest of the house, but not much. I have the vent to my kitchen turned off, and when I go into th ekitchen it's like taking a walk in the cool fall weather.
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