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Question DetailsAsked on 5/19/2012

I need more return air ducts. One contractor says I need seperate ducting back to furnace whereas the other wants to tie into existing.

I have a 3600 sg ft home (1800 first floor and 1800 in basement). My return ducts are 8" x 18". The duct at furnace is 10" x 25". The 1st installer says I need more return air ducts, but they shouldn't tie into existing duct as it is too small to accomidate more ducts into it and suggests running new ducts seperately all the way back to the furnace. The 2nd installer says he'd install new return air ducts into existing ducting system back to furnace (air handling system). My upstairs has 3 return air ducts in wall where-as the basement has 1 and it's in the ceiling vs wall, near the floor like upstairs. The 1st installer wants 1 extra duct upstairs. The 2nd wants 2 downstairs where they'd be installed at floor level. I think to balance the system the ducts should be in the basement but the warmer area, upstairs seems like it would pull more warmer air then basement. Can anyone suggest which duct placement is better and is it ok to tie into existing duct or run new ducting?

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5 Answers


As to where to add returns, the goal is to return the air that is supplied to each room, so I doubt adding return to basement is the way to go.

Definately run additional returns back to the furnace.

Though many refuse to believe it, it has been proven that the location of the return grille, high or low ,in the room has little effect on do what is easy to do.

Not sure why they are adding returns, though I don't doubt they are needed. it is usually due to rooms not being heated enough, or high static pressure ,which is resistance of the duct system to air flow.

When static is high, they should consider adding "turning vanes" to the elbows",90 degree turns" , in the main ducts. This is a simple way to reduce static, that most contractors fail to utilize. Ask about turning vanes, positive response, gets the job!

We replace around 750 systems per year , and 50% plus need added retuns ,due to high static. High static, will not let the equipment deliver the effieceny savings that it is capable of. So yes, it has been costing too much to operate since the day it was installed.


Answered 8 years ago by BayAreaAC


Thanks Bay Area. I may need to have added that my basement is 75% finished and isn't one big empty basement like many new/newer homes. I have 2 bedrroms, a rec room and full bathroom in basement and unfinished area of basement is approx 20 x 40'. Does that change whether the return ducts should be upstairs or down? Thanks for the vane information. I'll ask the installer about them.

Answered 8 years ago by Ron99218


Yes it does, I'm in Florida so no basements here , I was thinking unfinished. However he basement being under ground,likely needs less air flow then the floor(s) above.

The goal is return the amount of air supplied to a room,from that room. If we don't we "pressurize that room and force air out of the room,though craks around windows,up or down walls, etc..

Here's simple test to check returns. A pro would use a flowhood, but this will give you an idea of how the return are working.

Start with all interior doors open. Turn the furnace fan to "on" at the thermostat.

Feel the supply air flow in a room,then have someone close the door to that room,if the air flow is reduce much,then you need a return or return path from that room.

A return path can be ,more space under the door, or a grille in a wall that connects that room to a common area of the home that has a "large" return grille.


Answered 8 years ago by BayAreaAC


BayAire is on the right track. Let me start by saying hvacequipment is all designed and installed around building "Design Airflow.”None of this is "plug and play"! Although most people and contractorsact like it is. The first step you should undertake is to have a qualified"Air-Balancing" company come in to determine the "DesignAirflow" for your home first supply, and return. You need to take intoconsideration the problem may also exist in the proper amount of airflow being suppliedinto the space maybe inadequate. It seems the contractors are making thisassumption without even considering this as a variable in your situation.Through testing, a qualified contractor will be able to compare room designflow to actual flow. This will help you to see where your problems actual lieand better help the contractor lay out a game plan for addressing your airflowissues. I suggest you not let anyone arbitrarily install anything until youknow which rooms are being under/over served by the ductwork. Correcting yourissue is not a matter of placement in your home. It is a matter of looking atthe total system. The things that need to be evaluated are the room design,individual floor supply, and return airflow, ductwork capacity; no one can tellyou what capacity is by looking at it! It’s based on pressure produced by thefurnace, which brings me to my next point. You also need to know equipment btucapacity and furnace fan pressure capacity. It's possible your equipment maybeundersized for your home. No amount of balancing will correct this problem!This is why a highly trained and certified residential air-balancing company evaluatesyour home before you spend hundreds or even thousands of dollars on addressingthis problem. I have many of people (outside of my region) call me concerningthis same issue, because they did just that; spend money trying to fix thisproblem they continue to have today.


Answered 8 years ago by Stans HVAC


Thanks everyone, for your quick responses. I successfully had a new furnace and ac unit installed as well as two new return ducts.

Answered 8 years ago by Ron99218

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