2 of my 3 cold air return vents have almost no suction

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  #1  
Old 10-29-11, 04:19 PM
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2 of my 3 cold air return vents have almost no suction

I'm new here, so hopefully this is in the right spot.

I recently bought a new house. It's not brand new, but new to me. It's about 11 years old. It's a 1500 sq ft bungalow. There are 2 cold air return vents upstairs and 1 in the basement. 1 cold air return vent is in the living room almost directly above where the furnace is. This vent has a lot of suction. The other vent upstairs is down the hallway, about 30-40 feet. It has almost no suction and wouldn't hold a piece of tissue paper in place. The vent in the basement is almost directly below the weak vent upstairs, and it also has virtually no suction.

I tried blocking the good return vent to see if that made a difference, but it didn't, the other two vents still have almost no suction.

Is there an easy fix for this? Is it likely there's a big leak somewhere after the good vent and before the two weak vents? If so, and keeping in mind I have a finished basement, what is the best way to find this leak? Or is it just that my furnace isn't sucking hard enough to produce suction in vents much further away?

The regular vents throughout the house all work fine and appear to be balanced.

Thanks
 
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  #2  
Old 10-29-11, 04:56 PM
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Easy fix? No. What's causing it? Lousy design and/or installation.

Cheer up, probably 90% of residential duct systems have similar deficiencies so you are not alone. Wish I could give you better news.
 
  #3  
Old 10-29-11, 10:41 PM
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Okay, so what would the fix be? In fact, what is the cause? Is it likely a leak somewhere in the duct? Is the furnace just not producing enough suction? Where do I start?

I need to get this fixed as my woodstove is in my basement, so when I run the furnace fan, I want to distribute the heat from my woodstove to the rest of the house. That will happen easier and quicker if I can get the cold air return (which I have on my ceiling by the way, just for this very purpose) in the basement to produce enough suction.
 
  #4  
Old 10-29-11, 11:36 PM
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U need to have a heat load done then a proper duct design and size of the duct can be done
 
  #5  
Old 10-30-11, 12:22 AM
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As Airman states, you need to start at the beginning. You need to know the amount of heat your home loses on a room-by-room basis. You need to calculate the proper airflow to each room and you need to then calculate the proper size ducts. These are things that really need to be done when the house is designed but unfortunately it is far more common to have a heating contractor called in AFTER the house is framed and then he has to compromise and fit whatever ductwork he can wherever it will fit. The result is exactly what you have, a system that performs, but only barely.
 
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Old 10-30-11, 07:35 AM
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That's what I was hoping I wouldn't hear. Not surprised it's that complicated though.

So it's quite possible I would need to rip out a fair bit of ducting from my house after getting the heat load done? That would obviously be a problem as the basement is finished. Is there any type of quick fix that wouldn't entirely solve the problem but would allow me to get more suction out of the vent in the basement?
 
  #7  
Old 12-05-11, 08:32 PM
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Alright, As it's starting to get cold, the room that I have prepared for my 18 month old daughter over the summer is freezing. I live in a ranch style home, almost 2k sq ft upstairs. Half of the house has good suction, the other side (daughters side) has zero suction.

I went into the basement and noticed that there were some gaps in the duct work. I took some mastic and sealed as much as I could but ran out. Need to get some more. I am hoping that it will do something as it would be great to get some cold air pulled out of that room.

Right now, my house is set at 72 degrees. The baby monitor in her room has a temp indicator displayed in our room. It's at 61 degrees. HATE IT! Hope this helps some.

Would sealing gaps in the duct work with Mastic help?
 
  #8  
Old 12-05-11, 09:32 PM
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Most likely not unless there big holes. You have a duct issue. Have a heat load done.
 
  #9  
Old 12-06-11, 09:40 AM
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Hi Shaner, It sounds like you have major leaks in your duct work. Your post indicates that you have thought about it and probably diagnosed the problem. You have given us a bunch of reasons that it should be fixed, including a babies room being 10 degrees colder than the rest of the house. You have only given us 1 reason not to do it - the basement is finished.
You will have to take down the bulkheads that cover the duct work and find and seal all of the leaks. This includes the returns and feeds. You have to assume that the right sizes were put in originally (unless you want to have it all changed) and that when sealed, it will function properly. There is no other quick fix for it.
I have done a lot of basement renos and one of the things I do before closing the ceiling is to seal all duct work with mastic / foil tape (not duct tape). This ensures that the feeds and returns are doing what they are supposed to do - keep the whole house comfortable. It has taken me anywhere from 2 to 6 hours to complete but the clients notice the benefits right away. I have never found a system without leaks!
Once this is done, you can probably "tune" your returns to get more draw where you want it and draw some heat from the basement.

Good Luck with it!
Jim
 
  #10  
Old 12-06-11, 03:33 PM
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Most homes do not have major leaks. Most home do have a poorly sized and run and installed HVAC system. Having a properly designed and installed system will save big money over the life of a system. Hot and cold spots is always going to be a poor duct system design. Start with a heat load! This is the best tool for solving these issues.
 
  #11  
Old 12-10-11, 06:28 AM
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What is above and below your daughters room? There is a good chance that you also have inadequate insulation in that area of the house.
 
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