Basement Cold Air Return

16 years ago

I have a cold air return in my basement. I honestly don't know if this was added on when they finished the basement (my best guess) or if they were there when the home was built. The thing that concerns me is this return brings in more air than any other return in the house it seems. Is this normal for a cold air return (to bring in a lot of air)? It seems like they just tapped in to the main trunk line for return air and that's why it brings in so much air (as well as it being so close to the air handler). When the air handler turns on, the basement door is pulled shut by the velocity of the air. The supply air in the basement really doesn't seem to blow that hard; I believe it is just flex duct tapped into a main supply air trunk line (I believe the system consists of two main trunk lines for supply air).

Anyway, there's my situation. I was hoping someone could explain whether or not this is normal for cold air returns to bring in a lot of air (I guess this is important) and whether or not my situation needs attention.

Thanks in advance.

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Comments (9)

Tinmantu
16 years ago
I've seen homes that had inadequate duct systems, where they cut a big return in at the basement so the A/C would work properly...sight unseen, I don't know if this is the case. I hope there isn't a gas hot water heater in the same area. The solution to the door pulling shut may be to mount a grille on each side of the lower part of the door. If you have concerns, it may be worth paying someone that knows duct systems to come out and spend an hour looking around and offering solutions.
mikenew
16 years ago
What size return do you have upstairs?
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The builder doesn't create the ideal situation for everything when the leave an unfinished basement 'roughed-in'. We have an architech friend who knows the yahoo that designs the homes we're buying. While they are reputable, they do have a lot of design flaws - and these are greatly exaggerated when trying to finish an unfinished basement that is roughed-in/half done. There is a possiblity of moving the duct into the main basement, but it would mean creating ductwork that goes perpendicular to the joists, thus lowering the ceiling in that area. It may not be a big deal, but it's something I was hoping to avoid to save money (wasn't planning on hiring an HVAC guy when the basement gets done). The bedroom has one suppy vent - and the basement area has one also. My contractor has already told me I'll probably need to put in electric baseboard heaters, as that's not enough to heat a below-grade basement. And the basement finishing bill keeps getting higher!!!
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They're selling snake oil. There are so manys thing wrong with this proposal. First off, why do you feel you're not getting enough airflow? Is the room they used for their demo hard to heat or cool? If the existing 370 cfm is enough to keep that room comfortable, then there is no reason to pay money to increase the airflow. "More" is not always better. Your air handling system was designed to move air as an enclosed system. OF COURSE it's gonna move more air if you rig it to operate with the fan cover door opened. But again, more is not always better. I'll bet you could stand in that back room and *hear* the air rushing and whistling out of that vent after they took the blower door off. Your system should be set up to move the required amount of air as quietly as possible. You're also risking damage to the blower by making such a drastic change to the static pressure. The fan is designed to work against some amount of resistance. Lessen or remove that resistance and you could burn your fan motor out. A return in the basement is going to bring extra humidty and musty odors into your home. The air conditioning unit would have to work harder to remove the extra humidity. It could actually cost *more* money to operate. And if the unit was not capable of removing the extra humidity, you end up with damp air in your living quarters. This results in a cold, clammy feel that makes you feel uncomfortable. If you have some rooms that are hard to heat or cool, have a reputable HVAC company *calculate* how much air needs to go to each room. It's not a guessing game, and more is not always better. I noticed that you called the original installers and they blew you off. Forget them, they don't sound very professional. Try asking some of your neighbors for referrals, or check something like "craig's list". There has to be a reputable company in your area.
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An HRV is required by code on all new homes in the US. This is for ventilation air. I have one, works great. See link. Costs less than solar. An ERV will recover moisture too as well as heat. If you do not have a sealed combustion furnace (2 pipes, intake & exhaust) and have a gravity furnace, a combustion air duct is required to supply air for the furnace burner. You can create a "cold air trap" by placing a box on the floor and dropping the combustion air duct into the box (No top). You may also be able to connect the Combustion air duct to the return duct to the furnace (Check code). Attach duct at least 10'0" away from the furnace soas not to crack the heat exchanger with the cold air. Connecting to the return also creates a slight positive pressure in the house reducing infiltration/drafts. Stay Warm! Dan Martyn Here is a link that might be useful: Broan HRV
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" It is a very hard design to heat or cool evenly." That is undouptedly true and all the more reason not to mess around with diy, roll your own and home made desighn changes to hvac system. On the surface your idea sound's like there is a free lunch to be had pulling cool air from basement. It's far more complicated than sticking a return in the basement. For every cubic foot of air sucked from basement,another cubic foot must replace it. That make up air can only come from outdoors (a terrible idea) or withing the building(which is exactly how every room in building is usually desighned). Trade schools spend hours teaching techs this so just believe me when I tell you for every cubic foot of air "falling down stairs"another cubic foot already "falls right back up them". So if you want to heat and cool basement,you should have ducts in it. If you don't care to have basement heated and cooled,make certain there are no leaks in existing ducts ( both supply and return ). Now so you don't go away empty handed,a simple test that might tell you if theres a leak in supply or return in basement. Hang a bed sheet,thin plastic or similar light fabric to cover doorway leading to basement. If sheet moves toward basement there's a leak in return. If sheet moves away from basement there's a leak in supply. If sheet doesn't move at all the bad news is there's a "REMOTE" chance leaks of exact same size exist's in both supply and return. I'm assuming your air handeler is in basement or main trunks run through it,if not,little I've said is applicial for your house.
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ryanhughes
Original Author
16 years ago
Upstairs return barely gets any airflow, which is what concerns me.

Upstairs: 20x20
Middle Floor: 22x22
Basement: 14x14 (on ceiling right near furnace)

None of the grills have filters; the filter is located at the air handler. This is a 3.5 ton system.
ryanhughes
Original Author
16 years ago
I was hoping someone was familiar with the return air setup of typical 3 story homes. Logically, I guess the upstairs return would get less airflow because it is farther away from the air handler, but to what extent? Putting my hand by it I can barely feel it moving any air, but I do see some dust particles moving inside so I know it it bringing in air. Do cold air returns using bring in the most air in the basement?

Thanks in advance!!
bonanza_stu
16 years ago
What type of heat and how do you heat your water?

Returning from the basement can be against codes. If you heat with gas or oil there is always the possibility to pull flue gassed through the water heater chimney or draft diverter if the return is in the same room as the furnace or there is insufficient combustion air in the space.

Have a contractor check the pressure in the return duct. It may be possible to "redirect" where the air is being pulled from by blocking the basement return. Ideally, you want 60% of the return air to come from the high point in the system. Your description would indicate that is not happening.

The only time you want to return from the basement is if you wife has cold feet in the winter and she is spending a lot of time in the basement.

Good luck,
ryanhughes
Original Author
16 years ago
Thanks for the advise. The home is all electric so no worries on the code side of things.
dan_martyn
16 years ago
Ryan,

First of all you want a balanced system, if as you stated, you have a door between the basement and first floor, then the amount of return should equal the amount of the supply. Then your door won't slam. If there is a hard round duct somewhere between the basement return grille and the main return duct, you can put a manual balancing damper in pretty easy. If it's a rectangular duct, measure the size, you may have to have a contractor make you one. Now with a damper on the return you can damper down the return to match the supply. By dampering down the basement more return airr will be pulled in upstairs.

It's all a matter of balance,

Take Care,

Dan Martyn
ryanhughes
Original Author
16 years ago
Thanks Dan. I am going to call a professional in for an analysis of the whole system as I am considering replacing it.
blschap_aol_com
13 years ago
Yea I am going through the same thing, I am wondering that if you can close the grill do you need a damper, just a thought

Basement Cold Air Return

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