To air condition or open windows?

Geo-TH,In · May 10, 2014

I feel better closing windows to keep pollen, humidity, mold, dirt out and running A/C all summer.

I know some elderly who think they are saving money by opening windows and only turning A/C when house is very hot. Their house smells like a moldy sock too.

So I decided to crunch some numbers. Please check my math, could be wrong. If you have a 2000 sq ft house with 8 ft wally, you have 16000 cubic ft of air. Say humidity is 100%. Turn on A/c and lower humidity to 50%. My calculations show you have to pull a gallon of humidity out taking 8000 BTU's. So every time you open windows and let moisture in you may not be saving all you think. My calculations don't include energy cost to cool drywall or pull moisture out of carpet, furniture or drywall.

It seems to me like A/C's never stop pulling moisture out, so a gallon is a consertive figure.

VaTom · May 10, 2014

George, you have a point.

This is an issue I deal with often. My house is 20,000 cu ft, with a total air change every 2 hours (.5 Air Changes per Hour, ACH). Virginia isn't exactly a desert. I dehumidify during the season with a typical residential dehumidifier in my air system.

I had the opportunity several years ago to do a direct comparison to a similar high-mass house just down the road here. He needed a mortgage, which meant the simplest way to qualify the house was adding a tiny air source heatpump.

Neither house needs air conditioning as it is part of the passive heating/cooling system. Both houses are total electric. When we compared electric bills during dehumidification season, our increased electric consumption was the same: $1/day.

His heat pump consumed the same electricity as my dehumidifier. Our indoor temperatures remained the same as these high-mass houses never have much of any indoor temp change. His heatpump effectively was no more than a dehumidifier, but obviously cost considerably more to have installed than my $50 used dehumidifier. Just a necessary part of his house financing cost.

BTW, he's putting up with an 80 mile each way commute. Will NOT give up the house. He says the job isn't forever, the house is.

Scott 730 · May 10, 2014

Please let us know what dehumidification has to do with getting a mortgage where you live. :shock:

Dean · May 10, 2014

I have both AC and a whole house exhaust fan and have decades of experience with both.

I rarely use the AC, and, if forced to give up one or the other, would dispense with the AC in a heartbeat.

I open at least one window in each room about 2" in the evening before retiring and turn on the exhaust fan. The fan circulates cooler night air through the house during the night cooling it down to exterior ambient. Early in the morning, I close the windows and turn off the fan. The house is well insulated as are the windows and the house usually remains comfortable throughout most or all of the day.

Of course, there are expeptions to this practice and I do use the AC on the hottest summer days (almost never at night), usually on weekends when I am home more.

I would greatly miss the exhaust fan if I did not have it. I would miss the AC only occasionally.

Dean

ss55 · May 10, 2014

It depends on your climate and dew points.

When dew points are above 55F-60F when moisture will condense on cooler basement floors and walls, then running a central air conditioner makes sense to keep the house dry.

When dew points are low, night temperatures drop to near 60, and pollen isn't a problem, then opening the windows for a few hours in the early morning to cool down the house before starting the air conditioner can be more energy efficient.

jennifer408 · May 10, 2014

i agree with dean's logic. in addition we are considering adding a swamper. but when it gets hot the ac at home and in the vehicle goes on, life's too short to suffer through it. one other thing, i was reading a post awhile back about ac,heat pumps, etc...they were saying to expect to replace your hvac system every 10 years at an average cost of $8700. if you use your ac 4 times as much, your wear it out 4 times as fast. electrical use is a non issue for us cause we are off grid. we have solar power. ie. no electric bill

MarkB_MI · May 10, 2014

The worst thing you can do is to switch back and forth between A/C and ventilation. My wife LOVES to run the A/C all night, then throw the windows open in the morning. I've had no success in convincing her that she undoes most of the work done by the air conditioner overnight by filling the house full of humid air.

MarkB_MI · May 10, 2014

Scott, I suspect the house had electric resistance heat and wouldn't qualify for an FHA mortgage in that climate zone without installing a more efficient heat source.

VaTom · May 10, 2014

No Mark, the house had, and needs, no heating system beyond the passive one (which is not apparent to most). I added one borrowed 4' electric baseboard in my house to make the inspector happy, removed it after my final inspection.

4' for a house with 20,000 cu ft? Makes one wonder...

For an appraiser to come up with a decent value, they need to see something they can understand. No apparent heating/cooling system here doesn't work for them. This was a conventional mortgage.

His heatpump of course is electric resistance if it was used when it gets very cold here. We have small electric bills, until that $30/month bump summers for dehumidification.

VaTom · May 10, 2014

You have a problem. Same one I occasionally run into with house prospects living in high humidity locations. A visit here, or elsewhere with an air system usually solves the problem.

Guests here often remark on the quality of our indoor air. It lacks the high humidity, pollens, smoke, and other pollutants that outside air has. Lots of bugs outside, no window screens here. Enough glazing to feel almost like you're outside.

Recently had a house guest with extreme allergy to cats. Slept peacefully in the same room with our (indoor/outdoor) cat, no need for the arsenal of antihistamine he brought with him. Shocked him. Cat dander doesn't linger in the air, it goes outside to mingle with the pollens, smoke, and other pollutants.

Howard H. · May 10, 2014

Thats for sure, SS!

Our relative humidity has been running below 10-15% most of the time the past few months (with a low of 3%!! a few weeks ago).

The night air is usually very dry and cool in TX panhandle.

Howard

David G · May 10, 2014

George,

I am sitting at the airport, after dodging detours to get here, ready for a day of flying home.

You have been my chuckle so far.

Greg1959 · May 10, 2014

Yeppers! Sometimes some inspectors have some strange requirements. I once had an electrical inspector insist that I hook a grounding wire w/clamp to a water line to ground a newly installed breaker box instead of driving grounding rods into the soil. He would not pass inspection until I complied.

I showed him the house was plumbed with CVPC. He still insisted that I install the grounding wire and clamp to the water line. I just shook my head and clamped to CPVC water line. He passed the inspection at that time. I then reconnected the 2 grounding rods outside the home and reconnected to the breaker box.

Greg

VaTom · May 10, 2014

Wow... Must be a reason they're inspectors and not builders.

My guy said he couldn't force me to add that electric baseboard, but he'd sure like to see it. I complied, to get along. It worked, remainder of inspections went well. It wasn't the only thing I changed after getting my CO.

They've got a job to do, like you better if you make it easier.

Just went through a problem in Ga. There, for a non-standard house you must prove performance before getting a building permit. 68º in January is the proof they require. No problem, takes a lot of calculating and then a well-written paper.

So he's getting close to a final inspection and they tell him low e glazing is required. His glazing is custom, with 1/2" thick panes. Not 1/2" thick lites, the glass is 1/2" thick, huge panes. I argued against such thick glass, but he insisted. Thermally it's wrong, due to reduced transmission.

Panic City, Arizona. I calmed him down and explained that somebody there was authorized to grant him a variance. Which they owed him because they required proof of thermal performance before they issued the permit. That worked, low e requirement was waived.

Ideally, all these experiences turn into entertaining stories later.

john in la · May 10, 2014

You guys can open the windows if you like.
It is 85 degrees and 68% humidity outside right now.
Overnight the humidity regularly goes over 90%.

My A/C will be on till at least October.

Geo-TH,In · May 10, 2014

Howard,
I don't think I've ever seen 10% RH in Indiana.

Recently went to the Grand Canyon. I think the RH was 10%. I loved the Canyon, but my skin and sinuses didn't like the dry air.

If I had 10% RH, I would have a swamp cooler.

Do you have a pollen, mold and dust issue?
George.

LarryH · May 10, 2014

we open windows till 100 noticed guys who dont cant take hot days and are allergic to everything

Geo-TH,In · May 10, 2014

John,
Conditions in Indiana are similar to yours. If you want to live like the Amish, you need all wood floors, no curtains, leather sofa. Water will drip off basement walls and bathroom walls. So you will create indoor air pollution by not air conditioning and your place will smell,as my daughter says, like an old person lives there.
george

Geo-TH,In · May 10, 2014

Dave,

As long as you are laughing with me it's OK.

I'm surprised no one has challenged my calculations.

George

Pops1532 · May 10, 2014

I'm not sure what point you're trying to make. Is it what makes [i:edb4cea1cf]you[/i:edb4cea1cf] feel better, healthier conditions, or what's most economical? Or all three?

The economics of it aren't important to me. If I feel I need the A/C on, I turn it on. Mostly we keep the windows open. We live in Illinois and run the A/C 2-3 weeks a year. We don't have a problem with mold, odor, or dirt.

On the other hand I've worked in hundreds of smelly, moldy air conditioned houses. I think those issues have more to do with people's habits than whether or not they run their A/C.

Like I said, I like A/C when we have extreme humidity, but I generally prefer fresh air.

Howard H. · May 10, 2014

ha... The low relative humidity at our county seat (Cimarron OK) this year so far got down to 1%.

Three percent here in Stratford, TX where I live...

Pollen & mold not so much...

But the dust has been very terrible. We've been having dirt storms very bad this year... The drought is about as bad here as 2011 and that was the worst in quite a few years...

Howard

buickanddeere · May 10, 2014

Beats me how people think they are saving money opening the windows at night. After cooling and dehumidifying the house all day with peak priced power.
Now when the sun is down and little thermal load is being added to the house and the AC hardly runs. When power is cheapest. Just how does opening the windows and soaking the inside of the house with humidity make anything better? It takes very little all night to keep the house cool and dry.
I suppose somebody living in ad ry desert with very low humidity and cold nights. Then sure, not saving anything much but not re-soaking the house either.
The majority of AC's however are operated in high humidity locals. Keep the place sealed up, dry and cool.

Bret4207 · May 11, 2014

(quoted from post at 17:24:34 05/10/14) I'm not sure what point you're trying to make. Is it what makes [i:c05d465cff]you[/i:c05d465cff] feel better, healthier conditions, or what's most economical? Or all three?

The economics of it aren't important to me. If I feel I need the A/C on, I turn it on. Mostly we keep the windows open. We live in Illinois and run the A/C 2-3 weeks a year. We don't have a problem with mold, odor, or dirt.

On the other hand I've worked in hundreds of smelly, moldy air conditioned houses. I think those issues have more to do with people's habits than whether or not they run their A/C.

Like I said, I like A/C when we have extreme humidity, but I generally prefer fresh air.

Me too. We might run a window AC unit for 5-6 nights over the course of the summer. Wake up feeling lousy, headaches, etc. We get more out of leaving the windows open at night and closing them in morning, running ceiling fans. We have a mess of dogs and kids here and are in an out all day long. Our power bill is already in the $300.00 a month range in the summer, AC just makes it worse.

Do as you wish, to each their own. I think George is hyper sensitive to some odors and to air quality based on past comments.. I'd probably feel the same way if I had that problem.

Geo-TH,In · May 11, 2014

TOTALLY AGREE, seal up and dry up.

In Indiana schools have very few windows. In the summer, Schools are sealed, but not dry. So when your kids return to school in the fall, you have to take them to the Dr. for sinus infections, you need to go the school and smell the sick building your kids are attending.

However, there are some who think venting without A/C is the way to go.

Geo-TH,In · May 11, 2014

Bret,
Think, I know George and many other have sinus
problems. Spring is my worst time. Thank God for
sinus meds.

BTW, I think this is an economic issue for some.
I have over 2000 sq ft total electric house, with
3 garages on same meter. My fixed electric rate
from Duke is $134/mo. So why not run my A/C and
use less meds?

I also think it's an old school problem. I have an
85 year old tenant that wants to vent the basement
then thinks I should fix the moldy problem she
created.

The problem doesn't exist if you don't vent
basement. So this is more than just George having
a sinus problem.
George

Geo-TH,In · May 11, 2014

Tenants that don't use A/c let a a lot of dust, pollen and mold spores in. Can't imagine what a mess you would have in the country using a whole house fan and farmer is stirring up dust.

Bret4207 · May 12, 2014

(quoted from post at 06:52:28 05/11/14) Bret,
Think, I know George and many other have sinus
problems. Spring is my worst time. Thank God for
sinus meds.

BTW, I think this is an economic issue for some.
I have over 2000 sq ft total electric house, with
3 garages on same meter. My fixed electric rate
from Duke is $134/mo. So why not run my A/C and
use less meds?

I also think it's an old school problem. I have an
85 year old tenant that wants to vent the basement
then thinks I should fix the moldy problem she
created.

The problem doesn't exist if you don't vent
basement. So this is more than just George having
a sinus problem.
George

My wife and I both suffer from sinus issues George. But we don't live inside all the time, just can't do it.

NNP · May 12, 2014

I open windows.
hot or cold, I like fresh air.
(slight advantage where I live, the wind is always there, totally calm days are rare)
hot, turn a fan on me, if I move the fan moves with me.
I'm used to that from my shop. My floor fan moves around the job with me.
Since I retired, and got old and soft, I have a window air-conditioner in one room that I close off for a retreat on brutal days. Good family time too, with everyone retreating there.
As far as smells from moisture, whatever.
If my house smells, it has to be coming from somewhere.
Find it...clean it.

plant shade trees on the side of the house that the winds always come from. opening those windows on a brutal day with the breeze coming thru the trees feels just like air conditioning. smells good too.

mkirsch · May 12, 2014

"Old people's" houses often smell like moldy socks because of the moldy socks, not because they've got the windows open, figuratively speaking.

When you get older you don't move so well and you don't clean as much. A lot of stuff in older folks' homes hasn't been moved in decades. They gather dust and trap moisture, and many distinctive funks develop.

buickanddeere · May 12, 2014

Depends if you ask a HVAC engineer or a non technical member of the media .
I don't hear HVAC engineers telling people to open windows at night.

Bret4207 · May 13, 2014

(quoted from post at 06:26:46 05/12/14) Depends if you ask a HVAC engineer or a non technical member of the media .
I don't hear HVAC engineers telling people to open windows at night.

Well, when you think about it, HVAC engineers are sort of in the business of hoping you are using your HVAC, aren't they? The guy raising beef is always going to recommend beef for supper and the HVAC guy is going to recommend closing the windows and using a mechanical means of air exchange and tempering. Human nature.

buickanddeere · May 13, 2014

(quoted from post at 07:03:16 05/13/14)

(quoted from post at 06:26:46 05/12/14) Depends if you ask a HVAC engineer or a non technical member of the media .
I don't hear HVAC engineers telling people to open windows at night.

Click to expand...

Well, when you think about it, HVAC engineers are sort of in the business of hoping you are using your HVAC, aren't they? The guy raising beef is always going to recommend beef for supper and the HVAC guy is going to recommend closing the windows and using a mechanical means of air exchange and tempering. Human nature.

you are not getting it either.

The Hvac system running for a few hours on and off over night and in the morning. Just holding the temperature of a dry building. It's not working as hard as a continuously operating hvac unit removing water from a wet building from morning until mid day.

To air condition or open windows?

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