HVAC people, how do you fix air flow issues?

[Elixer]

This is a ~35 year old house, and the vents from the furnace have those levers in-lined with the heating/cooling pipe. They are all metal.
Problem is, no matter the combination of turning all levers to off, and turning them on one by one to try and detect which pipe goes to what room, gives any measurable difference in air flow.

When the lever is straight with the pipe, that should be on, and when it is at a 90 deg. angle from the pipe, it should be off right ?

So, why doesn't it make any difference no matter which way you turn the levers?
The pipes were all cleaned last year, so it can't be that.

Any ideas ?

Trying to fix 2 rooms that are always too cold in the winter, and too hot in the summer.



Moved from OT.

Anandtech Administrator
KeithTalent

 

[disappoint]

Pipe? Air flow? Usually forced air goes through ductwork. Pipes usually carry hot water or steam, depending on the system.

Yes steam is technically a gas, but people don't usually call it air.

Yes when the lever is straight with the pipe, that usually means on, and 90° is off or flow restricted.

Why it makes no difference no matter which way the levers are turned? Probably a restriction other than at the levers (valves).

Or maybe the ball valves (levered valves are usually ball valves) wore out and are allowing flow. All valves need to be replaced eventually. It's just a matter of time. Ball valves are usually better than gate valves but nothing lasts forever.

 

[wgusler]

You might have a return air problem. Where is the return? Are the room that are hot/cold far away from the return? Is there a return or does the furnace draw outside air?

Second issue may be a pressure leak in the ducts. Duct cleaning companies are sometimes a bit agressive with old ducting and knock joints loose.

Third may be a supply fan problem.

 

[disappoint]

You must have been calling ductwork pipe. Is that it?

 

[Greenman]

Check the duct work for leaks or breaks. Old duct work often breaks or rots. If it's wrapped with a gray paper like material, it's most likely asbestos, don't mess with it.

 

[Elixer]

You might have a return air problem. Where is the return? Are the room that are hot/cold far away from the return? Is there a return or does the furnace draw outside air?

Second issue may be a pressure leak in the ducts. Duct cleaning companies are sometimes a bit agressive with old ducting and knock joints loose.

Third may be a supply fan problem.

Each room has a return air grill at the top of the wall.
I would say it was a leak, except before and after the cleaning, the airflow is the same.

You must have been calling ductwork pipe. Is that it?

Yes, sorry... these are in between the ducts.

Check the duct work for leaks or breaks. Old duct work often breaks or rots. If it's wrapped with a gray paper like material, it's most likely asbestos, don't mess with it.

These aren't wrapped, or anything. Just bare metal.
I can only see 6 pipes..err ducts before they go into the wall. They all look OK, and no obvious air is leaking around those.

I was thinking there might be some kind of test to measure the output at each of the vents to see what they each read, since the warm rooms have lots of air, and the cold ones don't.

 

[disappoint]

Yes, sorry... these are in between the ducts.

No worries, they are round like pipes. Good luck with finding a solution.

 

[iGas]

Check the blower motor (oil/grease motor), belt, clean filter, pilot, burner, ignitor, return air duct for blockage.

http://www.trane.com/residential/en/for-owners/maintenance-tips.html

 

[MagnusTheBrewer]

The biggest problem is is usually leaking (untaped) duct joints, followed by inadequate air returns.

 

[jaedaliu]

Each room has a return air grill at the top of the wall.
I would say it was a leak, except before and after the cleaning, the airflow is the same.

No difference before and after just means that they didn't make the leak any worse after.

Yes, sorry... these are in between the ducts.

These aren't wrapped, or anything. Just bare metal.
I can only see 6 pipes..err ducts before they go into the wall. They all look OK, and no obvious air is leaking around those.

I was thinking there might be some kind of test to measure the output at each of the vents to see what they each read, since the warm rooms have lots of air, and the cold ones don't.

You can buy these sheets of magnets that go over vents. They hug the metal, and seal up the vent. You can use those to block ventilation to the good rooms, and see if the bad rooms get air. If not, you have a leak/block. If they do with good air flow, you have a pressure issue where the last rooms aren't getting enough air. That one's harder.

Is there a crawl space that you can get into to look at the ducting?

 

[MagnusTheBrewer]

Many times duct work is run through uninsulated outside walls or garages. In some older homes, part of the run is actually framed that is, instead of using metal duct, the space between wall studs is used. Cleaning is fine but, every single connection between the furnace/air handler and the registers should be taped.

 

[deadlyapp]

Each room has a return air grill at the top of the wall.
I would say it was a leak, except before and after the cleaning, the airflow is the same.


Yes, sorry... these are in between the ducts.

These aren't wrapped, or anything. Just bare metal.
I can only see 6 pipes..err ducts before they go into the wall. They all look OK, and no obvious air is leaking around those.

I was thinking there might be some kind of test to measure the output at each of the vents to see what they each read, since the warm rooms have lots of air, and the cold ones don't.

Oh they certainly do sell something that measures the output at the vents

http://www.aikencolon.com/Alnor-620..._p_2554.html?gclid=CP6CtPvJicICFW5p7Aodn3oAHw

Not sure if it's in your budget!

 

[Red Squirrel]

Cut a hole and take the dampers out then tape back shut. The old ones get misaligned with the lever and it's impossible to know how they're positioned if they even move at all. It's easier to just take em out. That's what I did. If you do need to control flow you can do it at the register, but typically you want the best flow anyway. I kind of see the idea of the dampers as you can fine tune the entire system to balance it but I find I rather just leave it wide open and control at the registers.

It is also possible you have insufficient return though. Also if you have a high end filter maybe replace with a cheaper one, some systems seem to not like the good filters.

 

[steppinthrax]

I'm not a pro HVAC guy, but I've replaced my entire heat pump and furnace by myself and have all the tools necesary as well as understanding of how these systems work.

What you essentially asking for is a AC duct balancing. That is to finely tune the dampers on those pipes you posted to a point where a equal amount of air is getting to both up/down stairs and other appropriate rooms.

In order to do this you will need a hvac anemometer which will measure the precises CFM flow across the vents. You will need to get the exact air flow coming from the supply plenum of the air handler and determine if your furnace is pushing out the correct CFM for the rated tonnage of the system. If correct then you need to get the CFM of all registers. If the total CFM is lower than the CFM of the supply plenum then you have a leak somewhere.

Once you've corrected the leaks then you can start balancing. Personally I will use mastic and aluminum foil anyway to seal the duct system real good before performing any balancing.

Anyway my suspicion for a 35 year old house is the duct work was design pretty shitty to began with. It wasn't until the 80s were they started adhering to standards for return/supply duct sizes. Your return could also be too small etc...

 

[nickbits]

Disconnected ducts or undersized blower is my first guess
Insufficient return air flow is another possibility

 

[steppinthrax]

You also need to measure temp difference between supply plenum and furthest air register from the unit.....

If there is too much of a diff then you have an issue.

 

[MrDudeMan]

Most people, including HVAC installers, overlook a critical element of the system: repressurization at the end of distributions. If the design of the system is incorrect, you basically can't fix it and no amount of tweaking will significantly help unless you rip out the main distribution areas.

This actually works very similarly to electron flow in a conductor with a terminated load at the far end. In a nutshell, even if you increase the blower motor torque by 5x, it may not actually increase airflow because the air has to pressurize after outlets in the main distribution duct. The last pick-off is often placed at or near the end of the main duct, which is incorrect. If the duct doesn't extend far enough past the last pick-off, the inside of the main duct will never pressurize and air transfer will be slow.

Your observations may not be related to this particular type of issue, but I really wouldn't be surprised if they are related because this is a very common mistake even in houses built over the last few years.

Do what everyone else suggested first and then evaluate the air pressure at various registers. If there's no noticeable change, you're probably looking at a bigger issue such as the one I mentioned above.

 

[T9D]

.....

 

[Scarpozzi]

Most people, including HVAC installers, overlook a critical element of the system: repressurization at the end of distributions. If the design of the system is incorrect, you basically can't fix it and no amount of tweaking will significantly help unless you rip out the main distribution areas.

This actually works very similarly to electron flow in a conductor with a terminated load at the far end. In a nutshell, even if you increase the blower motor torque by 5x, it may not actually increase airflow because the air has to pressurize after outlets in the main distribution duct. The last pick-off is often placed at or near the end of the main duct, which is incorrect. If the duct doesn't extend far enough past the last pick-off, the inside of the main duct will never pressurize and air transfer will be slow.

Your observations may not be related to this particular type of issue, but I really wouldn't be surprised if they are related because this is a very common mistake even in houses built over the last few years.

Do what everyone else suggested first and then evaluate the air pressure at various registers. If there's no noticeable change, you're probably looking at a bigger issue such as the one I mentioned above.

That sounds like a well thought out response.

I'd likely investigate myself if possible (depending on access to ductwork) and if I couldn't get to it, I'd pay someone to seek out the issue. If you've only got 2 rooms giving you trouble, there's a logical location to look for problems. From there, it should be possible to come up with culprits and solutions.

 

[Elixer]

Cut a hole and take the dampers out then tape back shut. The old ones get misaligned with the lever and it's impossible to know how they're positioned if they even move at all. It's easier to just take em out. That's what I did. If you do need to control flow you can do it at the register, but typically you want the best flow anyway. I kind of see the idea of the dampers as you can fine tune the entire system to balance it but I find I rather just leave it wide open and control at the registers.

Hmm, while at Lowes, they basically said the same thing, except to replace the current ones, with ones that have fans in them.

I also wonder if the dampeners are even working as they should, as you talk about.

Only problem with cutting them out is the wires that run along the sides of these ducts, and the fact that they are in the bottoms of the floor joist, so no real room to get a saw at them. Heck, one duct has no dampener, and it seems they just used the floor joist as the duct, with some sheet metal on the bottom.

Most people, including HVAC installers, overlook a critical element of the system: repressurization at the end of distributions. If the design of the system is incorrect, you basically can't fix it and no amount of tweaking will significantly help unless you rip out the main distribution areas.

This actually works very similarly to electron flow in a conductor with a terminated load at the far end. In a nutshell, even if you increase the blower motor torque by 5x, it may not actually increase airflow because the air has to pressurize after outlets in the main distribution duct. The last pick-off is often placed at or near the end of the main duct, which is incorrect. If the duct doesn't extend far enough past the last pick-off, the inside of the main duct will never pressurize and air transfer will be slow.

Your observations may not be related to this particular type of issue, but I really wouldn't be surprised if they are related because this is a very common mistake even in houses built over the last few years.

Do what everyone else suggested first and then evaluate the air pressure at various registers. If there's no noticeable change, you're probably looking at a bigger issue such as the one I mentioned above.

Yeah... looks like I got lots of work to do.
My fear is that it is a design flaw, and there is zero access to the ducts in those rooms at all, without breaking the wall down.

All the return air-ducts are the same size, except for one that is 3x the size of the others in the biggest room in the house.

Yeah the reason it must not make a difference is because you're throwing more air at it once the other ducts are closed. However it doesn't matter since that line can only move a certain amount of air. So it's either leaking some place or the line is just to small for the amount of heat or cold in the winter/summer that those rooms produce. And you'll need to make bigger lines.

But you could possibly fix some leaks, and insulate it better. And if possible try to shorten the run so there is less pipe to cause flow problems that lower the flow.

If you've ever had a plumber down there those guys are a-holes and will rip all kinds of pipe out of the way and damage it to do their plumbing. I once worked on a house where the idiot plumbers ripped the entire main trunk off the furnace where it went into the crawlspace. It was one giant open crevice. The lady had been complaining about low airflow.

Also wrong forum :biggrin: http://forums.anandtech.com/forumdisplay.php?f=67

D'oh, didn't see that forum section... Mods, please move.

The ducts that I see are out in the open, and while there is a crawl space, there is no way anyone but a kid that can fit through that hole...it is basically 14" x 14"x 12"
The meters are pretty expensive to measure the flow.

 

[Red Squirrel]

Wires? Are they electric dampers? If yes I would just make sure they work correctly and take advantage of them, you could zone out your system. If manual then I'd probably just take them out as the levers get loose and don't align with the disc anymore. On some there is a line on the screw where you can tell what way it's pointing inside but mine did not have that so it was a guessing game. Lever was wide open but damper was maybe half way. Shoved a camera in mine and half were almost all closed with dust bunnies blocking the rest of the flow.

 

[Elixer]

Wires? Are they electric dampers? If yes I would just make sure they work correctly and take advantage of them, you could zone out your system. If manual then I'd probably just take them out as the levers get loose and don't align with the disc anymore. On some there is a line on the screw where you can tell what way it's pointing inside but mine did not have that so it was a guessing game. Lever was wide open but damper was maybe half way. Shoved a camera in mine and half were almost all closed with dust bunnies blocking the rest of the flow.

Nope.. these wires are for electrical outlets I believe. They take the same path as the ducts.

 

[Red Squirrel]

Nope.. these wires are for electrical outlets I believe. They take the same path as the ducts.

Oh wow, so they ran wiring through ducts? Yikes. You can still remove the damper without removing the "duct" part of the damper though, but do be careful when cutting in there. For mine I just cut a C in the duct pipe, pealed up a flap, I then dented the damper in half inside and just pulled it out. Had to undo the wing nut on one side and the other side was just a pin going in a hole. I then pealed the C flap back and taped it up. Don't use "duck tape" but actual, duct, tape. It's shiny, almost metalic. Typically has a paper you peal off. Sticks very well.

 

[T9D]

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[boomerang]

I wonder how much actual planning is done in a typical HVAC duct system these days. Is it done in the field by the grunts doing the work or is it scienced out before hand or what? Yes, I know I've really oversimplified all that.

My home in Michigan if FA with floor registers and wall mounted returns. The airflow creates more noise than I like. The other morning it was unseasonably cold at 17 F and the system after coming out of setback eventually decided to ramp up to the highest blower speed and having not heard that in a long, long time I had to start checking to see if there was a fire in the basement because the noise was an actual roaring sound. There are no dampers anywhere although the main line does get smaller the farther away it is from the furnace and airflow does come out of all of the registers.

In Florida, we have an air handler literally stuffed in a closet. The front of the place is over-cooled to the point of it being cold in order for the back half to be comfortable. The conditioned air is taking the path of least resistance. Very short runs to the front of the condo and long runs to the back. Up in the attic are several distribution boxes but they all appear to be sized the same but I'm not interested in walking around up in there stooped over to really scope it out. I had the HVAC guy out to take a look at the system to establish a baseline (new purchase for us) and he was willing to go up there and look around but he was vague and non-committal on what if anything needed to be done or could be done. What I'm wondering is if it is worth it to have them investigate further.