Basement is much cooler than living areas: leave door open?

Factual Questions
1

This is my first time as an adult living in a home with a basement, and I haz questions!

For background: the basement has a painted floor but is otherwise not a finished living area. Right now, it’s the storage location for general crap.
The floor gets wet when it rains - no drips or obvious leaks, but water seeps in (or up?) and puddles in one area to about a half centimeter during storms.

It is, understandably, significantly cooler down in the basement. Right now, daytime temps are warm-to-hot. I realize that cool air falls downward and heat rises … so I don’t know if leaving the basement door open (to circulate the air) is better.

My engineer of a father is Team Door Closed, stating that any heat generated downstairs will rise into my kitchen and living room, and any cool air generated by the window A/C will go down the stairs into the basement.

That is the opposite of what I want, but I disagree with him.

As my basement contains no portholes to Hell that might admit heat, I am Team Open Door in the hopes that some of the cooler air in the basement will help keep down the temps in my home.
Would a fan at the stairs help?

Complicating matters is the humidity, and the fact that the basement is damp.

Assuming that for now I do not have funds to buy a separate dehumidifier for the basement … leave the door open? Shut it?

Some other options I haven’t considered?

Educate me on cohabiting with a basement, Dopers!

2

I would be on team keep door closed. A normal household fan at the top of the stairs isn’t going to “pull” enough air to make that much difference and would probably only circulate the air at the top of the stairwell.

You didn’t ask for some suggestion but I will throw some out. Try to cool your upstairs down by putting heavy curtains on your south/west widows to insulate the amount of heat coming through. Use your fan to try to move the cooled air around, sometimes a 2nd fan will make a big difference in getting the air to circulate

A little more expensive is to get a dehumidifier and use your basement as a living space. The dehumidifier with take care of the dampness but still have the natural coolness of the basement.

3

Based on always having lived in houses with basements – leaving the door open will not bring a significant amount of coolness. OTOH, if you have any general ‘mustiness’ in the air in the basement (and if you have high humidity, you will) THAT will quickly permeate your whole house. Your nose will adapt to it, but it’ll smack you and everyone else who enters from outside in the face.

Running a fan at the top of the fan might buy you a little more coolness but at the cost of more mustiness.

BTW, if you DO go for a humidifier, get one that drains into a sump hole if possible. Otherwise you’ll need to empty the thing a couple times a day, and carrying a plastic tub with an open top across the basement to a sink or whatever gets old very fast. Also, it will have a significant effect on your electric bill during the warm months.

4

To make use of the cool basement air, you would have to actually create a system such that air can circulate through the basement and the house. You need separate “in” and “out” paths for the air to flow. If you have a fan in the doorway blowing into the house, you would need a vent somewhere else in the basement so that air sucked out of the basement from the fan in the doorway is replaced by the hot air from another part of the house. This would create a circular path and you would get good airflow. If you just put a fan in the doorway, all you’re doing is churning the air in the area around the fan. It won’t really be sucking any air out of the basement.

5

Our basement is cool while the rest of the house is baking. We keep the door closed. I run a dehumidifier 24/7/365 in the basement. By keeping the door closed we have an escape from the heat (my finished mancave) and when things get bad I turn on some music and we can hang out down there.

If I leave the door open and run a fan, it makes the basement a bit warmer/more humid and yet has no appreciable effect on the rest of the house.

6

Yeah, I figured it couldn’t possibly be as easy as “leave door open, home magically becomes cooler.” That would be far too simple, eh?

These are all good suggestions, though! Please, keep 'em coming.

BTW: My biggest obstacle to using the basement as any sort of living area is the wiring, or rather the lack thereof. There’s only two outlets, and they’re on the damn ceiling.
If I was gonna stay for a while, I’d seriously consider having it re-wired. (Bonus: it would mean being able to use my electric dryer - currently you can only use a gas dryer.)

Hijacking my own thread: any guesstimate how much rewiring a basement would cost?

To un-hijack, it would mean i could plug in a dehumidifier down there …

7

When I bought my house, the inspector mentioned that he liked that there was a door to the basement (at the bottom of the stairs) and mentioned that I should keep it closed to keep cool air from the AC from going down there, where it would just be dissipated through the walls into the earth. Makes sense, and for the first year or so I did that. I also kept it open during the summer so any heat from the basement could make it’s way up the stairs. After a while I stopped doing that. It’s not like there was some noticeable difference.

Many, many years ago I started a thread asking about the feasibility of a ‘chute fan’. My idea was that you put a fan in your clothes chute that would draw cool air up from the basement and blow it into the main living area. Fellow dopers said it’s a bad idea since it could potentially draw CO from gas fired appliances in the basement and bring them into the house. I didn’t totally accept that since the basement door would be open for this to work so I imagine most of the makeup air would come from there. I never ended up doing it anyway.
However, what I think would be the real problem is radon. I think if you’re going to do anything that involves cycling basement air to the living area, you should find out how much radon is down there.
I know in my house, the radon level in the main living area is, let’s call it, boarder line and it’s much higher in the basement (I know, I know). Luckily I don’t spend much time down there, but I probably shouldn’t be blowing all that air upstairs.

TLDR, close the door in summer, open it winter. You want the cold air staying upstairs in warm weather and the warm air migrating upstairs in cold weather.

8

This deserves more attention. fans "push air in a specific direction very well, but they don’t “pull” air from a specific direction very well; they kind of pull air from all directions. So putting a fan at the top of the stairs to pull cool air up isn’t going to succeed. If you decide you want to circulate cool basement air upstairs, you’ll get better results if you place the fan down in the basement and angle it so that the fan’s exhaust plume heads upstairs.

9

But they also don’t push air very far and they particularly don’t push cold (heavy) air up very high. When I tried exactly this, a fan at the bottom of my stairs, directed upwards, couldn’t even be felt at the top of the stairway. Meaning, cool air was blowing about halfway up and falling right back down. I would have needed a booster fan in the middle somewhere.

What might work, however, would be some flexible ducting, maybe 8 or 12 inches in diameter with an inline booster fan. Put the end with the fan in the basement and run the duct up the stairs to the living area.
Essentially something like this, but home made so it’s not $250.

10

To exhaust the warm air out of the house I put a fan in the upstairs window of a north facing bedroom. It helps tremendously.

11

I think the more likely explanation is a lack of a path for the air to circulate. The fan is blowing towards the door, but that’s also the only place for air to come back into the basement, so the net flow is negligible. It’s like putting a box fan in your bedroom window. If you don’t open another window in the room or elsewhere in the house it won’t really do much but make a lot of noise.

The density difference of hot versus cool air isn’t that much. 10% for 50ºF is one number I found, so the difference between a basement and 1st floor is going to be only low single-digit percentages. I think it’s more the case that the cooler air just re-stratifies and settles back down rather than it being so hard to “push” up in the first place.

12

I have the same issue, or used to, sort of…

This can depend heavily on your HVAC system. My house is about 70 years old. Furnace and AC are modern, with forced fan. A single thermostat in the center of my home controls both and we don’t have any zones or such. One temp for the whole house.

My basement was always much colder (and still is somewhat cooler, but not as much after I sort of got things figured out).

I consulted with an acquaintance who works in HVAC and he told me what works. Seemed counterintuitive at the time, but makes sense now.

We leave the door open all the time. I was told that even though there are some cold air returns here and there, a major component of my type of system is free air flow up/down the stairway. I was also told that I need to keep the vents in the basement open at least partially, even when cooling. The idea with the one thermostat, one temp for the whole home is that the system is supposed to be mixing air from the entire home. Everything open allows the mix to happen.

Also, when our AC is on, we run the furnace fan constantly - the fan is blowing 24/7 as the AC compressor cycles off and on. This was also recommended by our furnace/AC installer. It helps cycle the cooler air in the basement and further balances out the warmer air upstairs with cooler air in the basement. The AC also acts as a dehumidifier. We only run a separate dehumidifier in the basement when the AC is not on.

The physics/chemistry in heating air vs. cooling air is different. In winter, we still leave the door open, but I close the vents in the rooms downstairs we don’t use as much. I supplement the basement heat with a space heater in my office but that’s it. And we don’t need to dehumidify in the winter because it’s so much drier and the ground is frozen where I’m at anyway. Hope that helps.

13

Isn’t a gas dryer cheaper to run than an electric?

14

Probably. But the basement is not wired to support plugging in a electric dryer.

Also, since it’s relevant, I do not have central air. In fact, the house has no air conditioning at all - a window unit was purchased when the heat wave started.
It’s situated across the house from the basement door, in case that makes any difference.

15

Leaving the basement door open allows the Things that live down there to get into the rest of the house, especially at night.

This may just mean food items occasionally disappearing from the fridge, but the implications could be more serious.

16

Just as a thought experiment, would it be feasible to use the coolness of the basement in some sort of heat-pump configuration? For example, run some metal ducting in a loop from the house to the basement and then back into the house and force air through it. The cool basement air will cool the ducting and the air flowing through it. Theoretically, the air coming out the other end should be cooler than the air going in, but I imagine the inefficiencies of such a system may mean the benefit is negligible.

17

You might want to look into why the basement is wet, in case it’s a simple fix. Two of the most common easy-to-correct things that can cause it: 1) blocked gutter/drain pipe causing rain to cascade down the outside wall and seep in; 2) earth sloped toward the house instead of mounded away from it, which letting rain seep down the outer basement wall.

18

I would have guessed (and it’s just a guess) that if you could blow the air to the top of the staircase, makeup air would be able to get back down the same way. Your staircase isn’t exactly a tightly fitted shroud. But turbulence and fluid dynamics and all that other stuff isn’t going to let this work anyway.
As for the difference between hot and cold air density, I’m not saying that cold air is that much heavier than warm air, just that cold air is heavy enough that a $10 box fan isn’t going to move it up a flight of stairs on it’s own.

Also FWIW, some furnace fans are set to spin the main blower faster when than AC is running and slower when it’s heating. I assume that’s mostly because it’s usually in the basement so it doesn’t need as much help to push warm air up as it does cold air.

19

I can think of one main reason why you shouldn’t leave the basement door open ---- mice!

I don’t care how old/new your house is, but I can pretty much guarantee that you will have mice, especially in an unfinished basement. That’s what basements are known for - plumbing, wiring, and mice.

The mice will love you for giving them an opportunity to enter your living area.

Other than that, I agree with the things others have mentioned. Yes, the basement is cooler in summer, and I guess you could get a powerful fan, which will cost between $80 and $300 and will be noisy, and use that to pull and circulate cooler air. It’s plausible and I’ve thought of that myself, but mice. No thanks. :slight_smile:

As mentioned above, the water thing could be caused by blocked gutters or missing gutters or water being directed toward the foundation of your house, usually due to bad grading.

But I’ve seen poorly placed sidewalks trap rainwater between the foundation and the sidewalk, preventing the water from running away from the house. I’ve also seen amateur landscaping close to the house that alters the grading and inadvertently leads to water being directed back toward the house, instead of away from it. Just watch the grading if you do any landscaping around the foundation.

Or, there might simply be a leaky pipe, which should be a fairly easy fix once you find it.

You might be better off buying a couple of window ac units or portable ac units? When you live in an area with a short summer season, it’s hard to justify anything too sophisticated and expensive, but there are some products, like Mitsubishi wall units, that can work in a room or two. They can provide ac in the summer and additional heat in the winter. I don’t know much about them, nor how much they cost, but it might be worth a look-see.

20

Or your water pipes could be sweating, not sure if city water arrives cold but it sure does from our well and drips abound at the pipes coming in the house and at the toilet tank and water filters. If we keep the ac on and direct small fans at the pipes they’ll dry up. Should have a dehumidifier in our walkout but very tight on space as it is.