Some HVAC questions

In this thread I asked if it was okay to put a return air vent in my basement.
My logic was this…my basement is coooold (in summer, I’d guess it’s about 5 to 10 degrees cooler then the rest of the house, it’s also not musty and I have a dehumidifier running to keep it nice and dry down there. My thought was that putting a vent in the return air duct would be helpful in two ways, 1)when the AC is running it wouldn’t have to work as hard since some of the air is already cooled and dry and 2)with just the fan running* it would bring some of the cold air up from the basement.
I got mixed answers for mixed reasons and I never did it. I would like to discuss this idea again.

First I wanted answer some of the questions that was asked.
1)The basement is more or less open to the rest of the house. There’s a door at the bottom of the stairs that we keep closed in summer and open in winter the keep the warm/cold air where it belongs, in the main living area.
2)There are two vents in the basement.
3)The basement isn’t musty and as far as I can tell doesn’t have any issues with mold or mildew.
4)The basement has only one finished room, but it has poured concrete walls and a concrete floor. This is a normal basement not a dark dank scary 'cellar"
So I ask again, is adding a return air vent in the basement a bad idea?

And for my crackpot invention/idea, I’ve always wondered about a ‘Chute Fan’
We have clothes chute that goes to the basement from the hallway, (BTW the house is only one story). Would it be a bad idea to put a small box fan in there to draw the cold air up from the basement?

*We have some god awful balancing (some rooms get really cold in winter, but we’ll save that for another thread so let’s not address that here) issues so sometimes I leave the fan running to try to even out the rooms.

Have you done a radon test in your house to see what the levels are? Radon gas tends to accumulate in the basements and sucking air in from the basement could cause problems if there’s a high level of radon in yours.

The only other problem I could see is if your house is tightly sealed and you’ve got new carpet/paint, as they tend to give off some rather noxious fumes. Another possibility you might consider is setting up a “heat exchanger” in the system. This would pass the ducted air through a radiator which would allowed the ducted air to pick up the temperature from the basement, without actually mixing with the air.

As for your heat balancing issues in the winter (yeah, I know you said you didn’t want to discuss it here, but I doubt if I’ll see the other thread devoted to it), if you have a kerosene heater, try putting it in the basement. When I was a kid we had the power go out for an extended period of time one winter, and since my mother was worried about the pipes freezing and bursting we put the heater down in the basement. The whole house quickly became toasty warm. I tried to convince my mother to keep the heater down there the rest of the winter, but she wouldn’t do it.

I re-read the prior thread (apparently, I killed it - sorry). I had some other thoughts about it that I didn’t put down at the time. It has to do with the temperature gradient in your home. As anyone with a two-story home can attest, it’s always too hot upstairs. Winter or summer, the challenge is to keep the first floor comfortable without roasting the upstairs. Adding a return vent in your basement will effectively make the basement the first floor. You say you keep the basement door closed in the summer to keep the cool air in place? Well, adding the return vent makes that door moot as far as the AC system is concerned.

Having said all of that, I may be mistaken. It would not be too difficult to add an opening, test out the effectiveness for a month or two, then seal it back up if it doesn’t work out. For a more thorough experiment, make the opening size variable, say with a sliding panel, so you can adjust the amount of return air pulled from the basement. You may find an optimum setting that does what you want. If you try this, let us know the results.

I should point out that the basement has the computer room (the only finished area in the basement) and it’s mainly for storage/laundry. I want to keep the first (main) floor comfortable, I’m not that concerened about the basement. It’s just that everytime I’m down here during the summer, I get to thinking about how much I pay to cool the first floor when there’s all this free cold air in the basement. It only seems logical (to me anyways) to want to bring some of it back to the first floor. The two logical (to me) ideas seem to be

  1. cutting a whole in the return ducting in the basemet
  2. my fancy pants 'chute fan)

You’re right, you’ll probably never see a thread for that. If it every REALLY bothers me (well, more then it does now) I’ll probably have to call someone in. I think I’ve tried everything that could be suggested. Everything from booster fans in the cold room (didn’t really work) and (what I thought would really work) Closing off (at the vents, not the dampers) all the vents in the rest of the house and opening all the returns in the rest of the house and then sealing the returns in the cold rooms and opeing the vents. The idea being that 90% of the heat would go into the cold rooms and then be pulled to the rest of the house…still didn’t work. Then I started messing the dampers…nope. Like I said if it ever really bugs me someday I’ll get an HVAC pro to actually look at it. BTW we just put a ceiling fan in a few months ago (in one of the warm rooms) and I’ve had some luck with turing that on and letting it bring the house to a equilibrium.

I doubt if your laundry chute fan could pump enough air upstairs to make much of a difference, unless it was so powerful that the noise from it sounded like a jet taking off.

It’s only about 4 feet long, I don’t see why setting a box fan in the opening (at the top) wouldn’t help. I’m not looking to air condition the house this way, just bring a little cool air upstairs.

I am an HVAC professional and work in this field. Some of the proposals in this thread and the other one I believe wouldn’t work. (and are incorrect)

A couple thoughts…

  1. Is the furnace or water heater gas/oil/LP fired; and if so, do they have open flues? (vs sealed combustion) If so, a return air in the basement may likely draw air from outside—through the flues. This is unsafe–very unsafe. Many codes do not allow basement r/a vents if there is gas fired equipment in the basement.

  2. How many square feet in the home, and what size air conditioner (in tons or Btus) do you have? Is there a reason you feel it needs “help”–or is this a logical idea to save utility dollars?

  3. The “load” in your house is comprised of 2 things–a sensible load (think temp) and a latent load (think humidity). The AC system must address both loads if you are to be comfortable. Of the 2, the latent is the hardest to handle, and the principle job of an AC system. The air in the basement may be cool–and that may help the AC to handle the sensible load. If however, the air in the basement is greater than 60% RH or so, you may be imposing a latent load on the AC system that is greater that the benefit of the cool air temps. In short it may not help at all, and—believe it or not—may make the AC system work harder.

  4. An outside air duct to your r/a duct is great for fresh air, particularly if this is a newer house with carpet off gassing etc. However…99% of HVAC installer wouldn’t know how to “balance” or set this up to optimize the ratio of return air vs. outside air (“ventilation” air) You may be getting a high ratio of outside air–this is good for fresh air and your health. (assuming the outside air quality near your home is good) But it is is expensive and unneccesary to heat and air condition the neighborhood—which is just what you’re doing if you’re running a high percentage of outside air. I would set this up so that the house is very slightly “positive”–just above “nuetral.” I would imagine that this means that the air in your home should be 90-95% recirculated, and 5-10% from the outside.

You can check to see if the house is positive: Turn on your furnace fan and open the front door 2 inches or so. Light a lighter in that 2 inch gap. If the flame stands straight, your home in nuetral. If the flame leans in to the home, the home is negative. If the flame leans out, the home is positive. You see that in commercial buidlings every day and don’t notice it. Ever been to a buidling where it was difficult to open a door, or air rushes in (or sometimes out) when entering/leaving? That is air balance issues, and a poorly set up home or building costs extra utility dollars.

Go outside and close off the fresh air intake and try it again. Even without sophisticated gear you should see a difference. Try it again with bathroom and kitchen exhausts on. In short, you want the home nuetral to slightly positive with the furnace on. If it is way positive (something you can’t measure with a lighter) you’re wasting energy dollars.

  1. A box fan is not designed to see any resistance at all. Even 4 feet may be enough that it will move little or no air. There are circulating fans made, however, that will do a nice job moving air through the laundry chute. Of course…it costs electricity dollars to run the fan. Is that more or less than the energy savings…? I’m not so sure… (and note 3 above suggests that it may not help at all…)

  2. I’d be very leery of closing off return air vents, anywhere. Restricted air flow will stress your furnace, and may cause premature heat exchanger failure. It’s worse in air conditioner. Reduced air flow can destroy your compressor outside in the back yard.

Theres more ideas, and if you want PM me and I’ll give you my phone number and my .02 :slight_smile:

ding ding ding, that’s all I needed to hear. That makes perfect sense. If I put a return in the basement and it can’t draw all of the air from the house, it’s going to pull from the chimney and that would be bad (carbon monoxide etc…)

As far as WHY I wanted to do it, it just seemed like a good idea, all that cold air in the basement, and I’m paying for cold air upstairs. It’s like paying to have your food delivered when the restaurant is fifteen feet away. So no go on the return air in the basement, and I suppose that rules out the ‘chute fan’ idea as well (since the basement door is closed in summer to keep the cold air that I pay for from going downstairs). As far as balancing, our house has something screwy going on with it. I don’t think (but I don’t remember) it’s that bad in summer, seems to be more of a heating issue. We just put in the ceiling fan last summer and it works okay for evening out the house except for two issues. One, to have it really move the air to the rest of the house it has to blow air down and since I don’t like it blowing on me the whole time, I’d rather it was blowing upwards. Two, with a toddler in the house we keep all the doors shut, so the fan idea doesn’t really matter anyways. Come to think of it, I don’t think it has as much to do with the HVAC unit itself as it is someother ‘force’ going on. For one, all the vents blow just fine, two one of the cold rooms is the ‘closest’ to the furnace and the other cold room one of the ‘further’ ones from the furnace (by means of ductwork) but they are both on the same end of the house. Oh well, not a big deal now that where into summer.

It was/is a good idea from a logical POV. From a practical POV, it probably isn’t.

The air in your basement has a very low sensible load—it’s cool. However, it likely has a high latent load—it’s humid.

It takes a lot more energy to de-humidify air, however, than it does to cool air.

So…the basement air is not “free air-conditioning”; the AC system will still have to “dry the air out”–to dehumidify. (which is why many home have dehumidifiers in the basement)

IMHE, I think the additional cost of dehumidifying this cool—but moist–air will be as great or greater than leaving all alone.

Plus the potential safety issues you mentioned. There are certainly other things you can do—like addressing the outside air ratio. But I think I’d leave the basement air situation alone.