All-

We recently moved into a home that had been flipped... some of the work was done OK, the rest not so well. I have spent the past couple of months reworking, repairing and finishing the work the flippers did.

One of the issues has to do with our return air vents. We have central air conditioning and forced air heat in a two story plus basement (its heated and air conditioned) row house. There are only two return air vents in the whole home (not uncommon from what I hear in older row homes where it is difficult to run ductwork), one return is on the main level of the home and the other is on the second floor. The AC/furnace are in the basement.

The problem we have, perhaps not a problem at all, that's why I am asking here, is that the return air vent on the main level of the house is very loud and sucks down a LOT of air while the vent on the second level of the house is barely able to hold a piece of paper up with the suction.

Any thoughts as to what might be causing the trouble? Is this a problem? Any suggestions for how to improve it?

Thanks!

I take it the vent that makes the noise is the closest to the furnace? Nothing much you can do except relocate or baffle the register. Have a hvac contractor check the system, you may be able to slow the fan down without creating other problems.

You're right, it is definitely the return closest the furnace is loudest. Unfortunately, not too many options to move it, the house is close to 100 years old. Now, that being said, how would one go about baffling it? The noise is basically the sound of the air being pulled in.

That being said, I am also concerned at how weak the upstairs return is. Is this a valid concern? Any suggestions for how to regulate it a little bit? Lessen how forceful it is on the main level thereby increasing the strength on the upper level?

Any thoughts?

Increasing the size of the ductwork would quiet the noise... but that's a big project. YOu could try a pleated filter in the return air opening. It would filter the air there, and the additional filter material could lessen the air flow, thus the noise. That would forsce more air to be returned through the other intake. But be careful you don't excessively block airflow to the system. It may be time to call a professional for some on site opinions.

As long as you are getting enough supply air then I wouldn't worry too much about the return. It may not have been sized to balance the return side but it is obviously working. As far as the pleated filters, I usually do not suggest them to my customers. The increased surface area gets plugged up faster and can cause air flow restrictions. In addition the pleated filters can cause a restriction even when new. When one of my customers insists on them then I make sure to check the heat rise across the exchanger to make sure it within factory specs.

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Originally Posted by Stubits

All-

We recently moved into a home that had been flipped... some of the work was done OK, the rest not so well. I have spent the past couple of months reworking, repairing and finishing the work the flippers did.

One of the issues has to do with our return air vents. We have central air conditioning and forced air heat in a two story plus basement (its heated and air conditioned) row house. There are only two return air vents in the whole home (not uncommon from what I hear in older row homes where it is difficult to run ductwork), one return is on the main level of the home and the other is on the second floor. The AC/furnace are in the basement.

The problem we have, perhaps not a problem at all, that's why I am asking here, is that the return air vent on the main level of the house is very loud and sucks down a LOT of air while the vent on the second level of the house is barely able to hold a piece of paper up with the suction.

Any thoughts as to what might be causing the trouble? Is this a problem? Any suggestions for how to improve it?

Thanks!

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You might give something like this a try. Used this design for years to quiet things down in return air ducts.

Thanks guys, a couple of follow-up questions.

Markwithak: How would I know I am getting "enough air supply"? There's an "OK" amount of air coming out of the supply vents, but could some adjustments to the return ducting improve that? I am OK leaving well enough alone, and while I am frustrated by the noise created by the main level return vent (it is REALLY loud), I wanted to make sure that the very limited return from the second level was not overly problematic.

HVAC1000- I am willing to try anything, but a couple of quick questions. I have heard that the noise is caused by having undersized ductwork, no? If so, wouldn't restricting flow cause additional noise? Would the baffle do anything to improve suction up on the second level? Finally, where do I go about buying a baffle, or is this something I can make on my own? If so, how?

Finally, and I know it is a bit extreme, but I think I could change out the duct work, relatively easily. That is to say, the return air duct is run through a vertical chase that goes directly from the basement, straight up to the attic. I think it is a sheet metal duct now, but I could probably tear that out and replace with flexible ducting somewhat easily, is that the real solution here? I'd prefer to avoid it, but want things to function corrrectly.

Thanks!

Yes noise can be caused by undersized duct both supply and return.


Restricting air flow can be a problem but you will never know about a restriction until you do a manual D. Look up on Google manual D for duct work.

My baffles were always homemade to comply with my design. I designed this originally for a very rich mans wife who could not stand any knid of noise. That was in 1971. Since then my design has been used many times without a problem since all my duct work is sized by manual D to start with.

HINT: it is made of plywood/covered with carpet and properly anchored.

Hvac1000-

Thanks for the info. I've just looked up manual D. It makes sense that there is a science to all of this.

Are there any specific resources you'd suggest that would allow me to calculate the appropriate duct work for the house?

Thanks!

If you search there are some free sites.

Thanks. I will work on this tonight.

From what I've read thus far, I think it is safe to assume that the return air duct is significantly undersized. I have many more supply vents than I do return vents. I would guess that both the return vents are connected to 8" flexible ducting, and again, there are only two.

Guess I have three questions, 1) I still don't understand, if the return is so undersized, why the system isn't sucking in more air, much more air from the second level return. Seems like it should be starving for air, no? And 2) what do I do now? Once I figure out how much return air I need, can I add additional return vents? How difficult is that? Again, given that the system is using the second vent so poorly, what do I need to do to make sure that it is using the return vents correctly? And finally, how bad is this for the system? Is it just less efficient? Am I not getting cooled/heated correctly? Or is this actually dangerous for the system?

Thanks!

I still don't understand, if the return is so undersized, why the system isn't sucking in more air,

You can only pull so much air down a pipe because you are horsepower limited. Put a bigger motor on it and if the motor is large enough you can collapse the duct or suck small dogs and cats up against the grill so they cannot escape. Do not laugh I have seen this before.

I have many more supply vents than I do return vents.

The number makes no difference it is the total number of square inches that count.

Once I figure out how much return air I need, can I go ahead and add additional return vents?

You can do whatever you want.

How difficult is that?

Could be a big pain in the A$$. You will need some special tools if you are going to work with metal and flex duct while easier to work with may not fit due to the larger size requirements of the flex.

Again, given that the system is using the second vent so poorly, what do I need to do to make sure that it is using the return vents correctly?

Do a manual D for your system and repair or replace the duct to make the system work properly. You will also need special tools/meters to balance the system since that is the only true way to determine if the return air's or supply's are doing there individual air movement as per design specs.

how bad is this for the system?

It can stress the system components. Blower motor, A/C and heat. The unit is probably not moving enough air to allow the A/C system to move the proper amount of air across the inside coil. This can cause a out of range condition not allowing the proper TD (total differential between the supply and return air temps). On heating it can cause the heat exchanger to be overheated causing short cycling of the burner Etc. There are more items than this but I am not going to operate a school here I get enough of that at the university. LOL

What this all comes down to is the fact that you have a problem and you have been told or given a direction to go on so you can figure out how to make corrections. If I may suggest calling a local HVAC company for a on site inspection and estimate for what it will take to make your system correct and within the specifications called for in the standards. This way you will get a better idea of what is actually involved and the approximate costs. Then you can decide if you want to do it yourself or have it done. While the contractor is there they might do a manual D at a nominal price for you to make it easier to figure out the duct sizing and square inch requirements.

Does the air conditioner keep you cool. Does the furnace keep you warm. Can you sleep at night with the noise. If so, don't change a thing.

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Originally Posted by MarkwithaK

<snip>As far as the pleated filters, I usually do not suggest them to my customers. The increased surface area gets plugged up faster and can cause air flow restrictions. In addition the pleated filters can cause a restriction even when new. When one of my customers insists on them then I make sure to check the heat rise across the exchanger to make sure it within factory specs.

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Mark,

In the interest of other readers that might condemn pleated filters out of hand after reading your post, I would like to add my 2 cents.

You didn't say what you are comparing the pleated filter to, but I assume "hog's hair". In my opinion, hog's hair filters are only effective at catching mice and small birds, so yes, a pleated filter will catch more dirt. We have changed almost completely to pleated filters in our group homes, most of which can take the 5" thick "change once a year" filters. I have done some static pressure checks on these filters and find that even when they look dirty, they still have not increased the pressure drop significantly. My baseline on one of the recent ones that I was checking was 0.36" to 0.42" wc and I replaced it a year later somewhere around 0.74" wc. That system has a pretty fast airflow. The filter was pretty bad looking, but that house is very low humidity. The only problems we have had are on the 1" thick ones on systems with high air velocity. They flexed too much. When they do work, (recommended change interval - 3 mo) at the end of their life there isn't a great difference in static pressure drop. Even when they look bad. I don't like them nearly as well as the 5" ones.

I am pretty well sold on pleated filters, our houses that have them have less problem with dust and the evaporators do stay cleaner longer. I do agree though, on your note about checking the temps across the exchanger.

Some of the best materials made for HVAC air filters is polyester when used with the correct filter frame rack. Been using that material for over 27 years and no complaints here. Some of the polyester material already has a sticky substance attached to it and some you need to spray with filter coat. Due to the variable density construction of the material they start loading deep in the filter then to the outer face of the material. Over the years we have converted many hospitals and other types of clean rooms to the polyester design. Statistics prove that polyester has the best entrapment quality over other brands. They do catch a lot of dirt so they need to be changed more often than the 5 inch pleated filter blocks but who wants all that dirt hanging around for a year until the next filter change.

Everybody likes different filters that is why they make so many different kinds. LOL

EP I appreciate your input and I please allow me to clear up my comment. I have no problems with plated filters per say. My comment was based upon a couple of specific instances. The pleated filters do work great and I will never argue about that. In fact I use, as a general rule, a pleated MERV 7 in my commercial equipment.

I do however have a couple of issues with them. If the system was not designed properly and is already on the edge of the acceptable range as far as heat rise then a pleated filter can actually hurt the system. Example: One of our clients has a convenience store that is using 2 residential systems twined together. The building has very high vaulted ceilings and air flow is a major concern. With a pleated filter the units would over heat within 5 minutes of operation.

My other concern is simply the advertisement on the filter packaging can be misleading. Your typical homeowner will see that they are good for 3 months, replace their filter with the pleated variety and forget about it. If that house has a high dust count, or several pets etc. etc etc. then that filter is going to reach it's capacity sooner than 3 months. The problem is that most homeowners do not realize that and will let it go for 3 months because that is what the packaging said. If the homeowner is diligent about their maintenance then its not a problem, but in my experience the filter will be the last thing on their minds.

If I wrote the instructions on the package of any filter it would read : Maximum life of three months. Check once a month and replace if neccesary:. Except for one year filters then it would say(max one year, and still check monthly. Like mark said, there are many factors as to how fast any filter can become clogged and hurtfull to the system.

Mark and mgd77,

I agree with both of you, I just wanted to make certain that there was a positive note for the pleated filters. High dust levels definitely do kill them early, but at least they catch it as opposed the hogs hair.

ERM