I'm now totally confused. The installer of my new furnace and a/c told me to shut down (cover up with sheet metal) the air return that is on the ceiling duct. Fine.. however my basement is finished and so is the utility room that houses my furnace and washer/dryer. My crawl is open to the utility room and the crawl is not vented to the outside. The crawl is a concrete floor with 20 year old fiberglass insulation on the walls.
The return is in the finished basement just past the Levoured door that separates the finished basement from the utility room.
I'm not sure if the installer is correct in his advice about the return. The return is 15x10. The finished basement has three registers located on walls just above the floor.
The installer said that at the very least the return is too big and that is is sucking all the basement air including the fibers in the insulation and sending it throughout my house... In other words he scared the hell out of us. We have kids.
A neighbor told me he thinks a return is required in order to make code. So I we t to my local building dept. The supposed expert seemed confused and when I told him I took out all the necessary permits and all facets were inspected, he got up to go talk to someone else and returned saying that the return is required and "has to be 100% the size of the registers" in other three 6x10 registers would require a return that's 180 inches square feet.
I mentioned this to a local Fireman who has also been doing HVAC work for 22 years and he said that's nuts, adding the return shoud be cut by one third.
Any information, comments, or information would be appreciated.

You need a return to balance the air flow. Otherwise you get no circulation. You really need a test and balance done and anyHVAC company can do that.

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Can this return actually be sucking in the fibers from the crawl space fiberglass insulation? Should I remove it?

If the return is in the crawl, yes. A lot of HVAC people size the return at 80-90% of the supply.

The air return is 10 feet from the crawl. It that sufficient space to prevent pulling insulation fibers in?

Yes. Is the crawl space closed off?

No it's open. Supposedly the code says if it's vented to the outside it has to be closed off and if it's not vented to the outside it should remain open because it's a part of the conditioned area. I just measured and the return actually 8 feet from crawl .

Is this return the only return for the system?

It's the only return in the basement. Each room on the 1st and 2nd floors has a return with the exception of the kitchen and bathrooms.

Suspect installer wanted you to block the basement return because being so close to the system most of the return air will come from there. Personally I wouldn't be too concerned about insulation fibers being being pulled through the moisture barrier and circulated through the house Any fibers would be trapped by the filter.

Block or restrict the basement return, you need to pull air from the upper floors to cause circulation and even, balanced heating and cooling. Put a plastic bag over the basement return temporarily while the system is running and feel the change in return air being pulled in from the upper returns. Use this method of partially blocking the basement return to achieve even temperature through out the house.

Thank you very much for your help. I've asked a number of HVAC people, some more experienced than others, and you are the only one that has been able to understand my questions and answer them in a way I can understand. The HVAC guy who put in the furnace is coming back tomorrow to decrease the size of the return. Hopefully he will know how to test the system to determine just how big the return should be but it definitely sounds like it is probably to large.
Do you have any preference as to the type of filter to use? The furnace came with a washable/vacuumable one however some say toss it and get a cheap pleated one instead because they work better?u

You nailed it Harold.

Unless you have allergies or some other medical condition I think the type of filter is a matter of personal choice and convenience.

Personally if it were me, I would cancel the HVAC tech. The best he can do is make an educated guess. Granted that guess will be based on experience. You can run all kind of numbers but there is just too many factors, such as how open the upper floors are, shape and turns in the stairways, whether doors are normally open or closed, to develop any reliable calculations. Based on his earlier instructions, the installer must think you don't need any return from the basement.


I would tape a piece of plastic over the basement return and see how the system performed as far as even distribution of cooling. You don't usually need much heating or cooling in a basement and unless the system is air tight you will probably get enough air return from around the system itself. If you find you don't have enough cooling in the basement, remove a portion of the plastic. When you have the temperatures balanced through the house, remove the grill of the basement return and cover the opening with plastic and tape. Reinstall the return grill. You won't even have to do any repair to the ceiling or any painting.

You may find that you need a different size return for the heating season. Or you may not. After you know the maximum size return you need, you can permanently reduce the size of the return to the maximum needed. Then install a supply registrar which will give you a convenient way of adjusting between heating and cooling if needed.

I had the HVAC tech come anyway. They had told me their would be no charge to block the return. I resisted permantely sealing the return even though he insisted I didn't need it and he swore that his finished basement has absolutely no return. He also said the furnace would not be damaged if the return was permanetly or seasonally sealed. He told me that if I wasn't sealing the return I might want to cover it during the a/c season with a "frost king metal magnet" which could easily be taken down when the heating season arrives. (My 2nd floor a/c has been weakish in summer).
I went out and found a "frost king vent magnet" however on the package I found the cautionary statement "do not use on return intake vents". I asked a worker at the store why the caution and he said that the company probably didn't want anyone suing them by "blowing up their HVAC system".
The HVAC company that installed my new furnace and a/c have been around my area (Chicago) for generations but what good does that do me.
I think I did figure one thing out for sure today. The HVAC guys always recommend the cheaper filters saying they worked as good or better than the expensive ones. It finally dawned on me after doing a little Internet reading that what the HVAC guys are referring to is what's best for the furnace and not what's best for a homes healthy air.
Anyway, as you stated without the correct assessment of the factors involved there is no way to know for sure what to do. I quess I just have to play with it, maybe the plastic thing, hoping the furnace or A/c aren't damaged in the process.
I was somewhat relieved to be told not to be too concerned with the fiberglass fibers from the crawl but because I always used cheap ones I wonder if any such fibers were actually caught .
This has been quite an experience for me and I'm still after a solution.



Has been around my area (Chicago) for generations but what does that mean anymore